text:
Taylor, C.
D. C. 'Niobium-Titanium Superconducting Material s ', in S.14, 1982 HIGH-FIELD SUPERCONDUCTING ACCELERATOR MAGNETS C.SUMAG-68 HIGH-FIELD SUPERCONDUCTING ACCELERATOR MAGNETS* C.
Taylor, C.
D. C. 'Niobium-Titanium Superconducting Material s ', in S.Nb -Ti and Nb3Sn superconductors. , ĢĢ ,""" s. S. Clamp, Tie14, 1982 HIGH-FIELD SUPERCONDUCTING ACCELERATOR MAGNETS C.
High magnetic field ohmically decoupled non-contact technology
Wilgen, John (Oak Ridge, TN) [Oak Ridge, TN; Kisner, Roger (Knoxville, TN) [Knoxville, TN; Ludtka, Gerard (Oak Ridge, TN) [Oak Ridge, TN; Ludtka, Gail (Oak Ridge, TN) [Oak Ridge, TN; Jaramillo, Roger (Knoxville, TN) [Knoxville, TN
Methods and apparatus are described for high magnetic field ohmically decoupled non-contact treatment of conductive materials in a high magnetic field. A method includes applying a high magnetic field to at least a portion of a conductive material; and applying an inductive magnetic field to at least a fraction of the conductive material to induce a surface current within the fraction of the conductive material, the surface current generating a substantially bi-directional force that defines a vibration. The high magnetic field and the inductive magnetic field are substantially confocal, the fraction of the conductive material is located within the portion of the conductive material and ohmic heating from the surface current is ohmically decoupled from the vibration. An apparatus includes a high magnetic field coil defining an applied high magnetic field; an inductive magnetic field coil coupled to the high magnetic field coil, the inductive magnetic field coil defining an applied inductive magnetic field; and a processing zone located within both the applied high magnetic field and the applied inductive magnetic field. The high magnetic field and the inductive magnetic field are substantially confocal, and ohmic heating of a conductive material located in the processing zone is ohmically decoupled from a vibration of the conductive material.
Materials Physics Applications: The National High Magnetic Field...
Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)
Pulsed Magnetic Field Laboratory of the NHMFL in the form of a 1.4 GVA inertial storage motor-generator for high field pulsed magnets. In addition to the 60 Tesla Long Pulse Magnet...
Improving magnet designs with high and low field regions
Bj°rk, R; Smith, A; Pryds, N
A general scheme for increasing the difference in magnetic flux density between a high and a low magnetic field region by removing unnecessary magnet material is presented. This is important in, e.g., magnetic refrigeration where magnet arrays has to deliver high field regions in close proximity to low field regions. Also, a general way to replace magnet material with a high permeability soft magnetic material where appropriate is discussed. As an example these schemes are applied to a two dimensional concentric Halbach cylinder design resulting in a reduction of the amount of magnet material used by 42% while increasing the difference in flux density between a high and a low field region by 45%.
Optical pumping magnetic resonance in high magnetic fields: Characterization of nuclear relaxation during pumping
Augustine, Mathew P.
Optical pumping magnetic resonance in high magnetic fields: Characterization of nuclear relaxation during pumping Matthew P. Augustine and Kurt W. Zilm Department of Chemistry, Yale University, New Haven exchange with optically pumped Rb vapor is investigated in high magnetic field. Operation in a high field
High magnetic field processing of liquid crystalline polymers
Smith, Mark E. (Los Alamos, NM); Benicewicz, Brian C. (Los Alamos, NM); Douglas, Elliot P. (Los Alamos, NM)
A process of forming bulk articles of oriented liquid crystalline thermoset material, the material characterized as having an enhanced tensile modulus parallel to orientation of an applied magnetic field of at least 25 percent greater than said material processed in the absence of a magnetic field, by curing a liquid crystalline thermoset precursor within a high strength magnetic field of greater than about 2 Tesla, is provided, together with a resultant bulk article of a liquid crystalline thermoset material, said material processed in a high strength magnetic field whereby said material is characterized as having a tensile modulus parallel to orientation of said field of at least 25 percent greater than said material processed in the absence of a magnetic field.
High magnetic field processing of liquid crystalline polymers
Smith, M.E.; Benicewicz, B.C.; Douglas, E.P.
A process of forming bulk articles of oriented liquid crystalline thermoset material, the material characterized as having an enhanced tensile modulus parallel to orientation of an applied magnetic field of at least 25 percent greater than said material processed in the absence of a magnetic field, by curing a liquid crystalline thermoset precursor within a high strength magnetic field of greater than about 2 Tesla, is provided, together with a resultant bulk article of a liquid crystalline thermoset material, said material processed in a high strength magnetic field whereby said material is characterized as having a tensile modulus parallel to orientation of said field of at least 25 percent greater than said material processed in the absence of a magnetic field.
Magnetic Field Safety Magnetic Field Safety
McQuade, D. Tyler
Magnetic Field Safety Training #12;Magnetic Field Safety Strong Magnetic Fields exist around energized magnets. High magnetic fields alone are a recognized hazard only for personnel with certain medical conditions such as pacemakers, magnetic implants, or embedded shrapnel. In addition, high magnetic
Journal of Magnetism and Magnetic Materials 281 (2004) 272275 Effects of high magnetic field annealing on texture and
Garmestani, Hamid
Journal of Magnetism and Magnetic Materials 281 (2004) 272┬Ł275 Effects of high magnetic field annealing on texture and magnetic properties of FePd D.S. Lia, *, H. Garmestania , Shi-shen Yanb , M China c National High Magnetic Field Laboratory, Florida State University, 1800 East Paul Dirac Drive
Mitigated-force carriage for high magnetic field environments
Ludtka, Gerard M; Ludtka, Gail M; Wilgen, John B; Murphy, Bart L
A carriage for high magnetic field environments includes a first work-piece holding means for holding a first work-piece, the first work-piece holding means being disposed in an operable relationship with a work-piece processing magnet having a magnetic field strength of at least 1 Tesla. The first work-piece holding means is further disposed in operable connection with a second work-piece holding means for holding a second work-piece so that, as the first work-piece is inserted into the magnetic field, the second work-piece is simultaneously withdrawn from the magnetic field, so that an attractive magnetic force imparted on the first work-piece offsets a resistive magnetic force imparted on the second work-piece.
Magnetic Fields in High-Density Stellar Matter
German Lugones
I briefly review some aspects of the effect of magnetic fields in the high density regime relevant to neutron stars, focusing mainly on compact star structure and composition, superconductivity, combustion processes, and gamma ray bursts.
Study of HTS Wires at High Magnetic Fields
Turrioni, D.; Barzi, E.; Lamm, M.J.; Yamada, R.; Zlobin, A.V.; Kikuchi, A.; /Fermilab
Fermilab is working on the development of high field magnet systems for ionization cooling of muon beams. The use of high temperature superconducting (HTS) materials is being considered for these magnets using Helium refrigeration. Critical current (I{sub c}) measurements of HTS conductors were performed at FNAL and at NIMS up to 28 T under magnetic fields at zero to 90 degree with respect to the sample face. A description of the test setups and results on a BSCCO-2223 tape and second generation (2G) coated conductors are presented.
Mechanical design of a high field common coil magnet
Caspi, S.; Chow, K.; Dietderich, D.; Gourlay, S.; Gupta, R.; McInturff, A.; Millos, G.; Scanlan, R.
A common coil design for high field 2-in-1 accelerator magnets has been previously presented as a 'conductor-friendly' option for high field magnets applicable for a Very Large Hadron Collider. This paper presents the mechanical design for a 14 tesla 2-in-1 dipole based on the common coil design approach. The magnet will use a high current density Nb{sub 3}Sn conductor. The design addresses mechanical issues particular to the common coil geometry: horizontal support against coil edges, vertical preload on coil faces, end loading and support, and coil stresses and strains. The magnet is the second in a series of racetrack coil magnets that will provide experimental verification of the common coil design approach.
The National High Magnetic Field Laboratory
Weston, Ken
of Contents Table of contents cHaPTeR 1 The Year in Review 6 cHaPTeR 3 Magnets & Materials 44 cHaPTeR 4 User The year in Review cHaPTeR 1 The Year in Review by Gregory Boebinger, MagLab Director 2012: Another
Weston, Ken
, and Geochemistry 14 MAGNET SCIENCE & TECHNOLOGY Engineering Materials, Instrumentation, and Magnet Technology Magnet Science & Technology 42 7 including Engineering Materials, Instrumentation, and Magnet TechnologyNATIONAL HIGH MAGNETIC FIELD LABORATORY REPORTSVOLUME 12 Ę N0. 1 Ę 2005 OPERATED BY: FLORIDA STATE
Homogenous BSCCO-2212 Round Wires for Very High Field Magnets
Dr. Scott Campbell
The performance demands on modern particle accelerators generate a relentless push towards higher field magnets. In turn, advanced high field magnet development places increased demands on superconducting materials. Nb3Sn conductors have been used to achieve 16 T in a prototype dipole magnet and are thought to have the capability for {approx}18 T for accelerator magnets (primarily dipoles but also higher order multipole magnets). However there have been suggestions and proposals for such magnets higher than 20 T. The High Energy Physics Community (HEP) has identified important new physics opportunities that are enabled by extremely high field magnets: 20 to 50 T solenoids for muon cooling in a muon collider (impact: understanding of neutrinos and dark matter); and 20+ T dipoles and quadrupoles for high energy hadron colliders (impact: discovery reach far beyond present). This proposal addresses the latest SBIR solicitation that calls for grant applications that seek to develop new or improved superconducting wire technologies for magnets that operate at a minimum of 12 Tesla (T) field, with increases up to 15 to 20 T sought in the near future (three to five years). The long-term development of accelerator magnets with fields greater than 20 T will require superconducting wires having significantly better high-field properties than those possessed by current Nb{sub 3}Sn or other A15 based wires. Given the existing materials science base for Bi-2212 wire processing, we believe that Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub y} (Bi-2212) round wires can be produced in km-long piece lengths with properties suitable to meet both the near term and long term needs of the HEP community. The key advance will be the translation of this materials science base into a robust, high-yield wire technology. While the processing and application of A15 materials have advanced to a much higher level than those of the copper oxide-based, high T{sub c} (HTS) counterparts, the HTS materials have the very significant advantage of an extremely high H{sub c2}. For this reason, Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub y} (Bi-2212, or 2212) in the form of a multifilamentary Ag alloy matrix composite is beginning to attract the interest of the magnet community for future extremely high-field magnets or magnet-insert coils for 4.2K operation. Fig. 1 shows an example of excellent JE (engineering current density) in Bi-2212 round wire at fields up to 45 T, demonstrating the potential for high field applications of this material. For comparison, the Nb{sub 3}Sn wires used in magnets in the 16-18 T range typically perform with J{sub E} in the range 200-500 A/mm{sup 2}; the Bi-2212 wire retains this level of performance to fields at least as high as 45 T, and probably significantly higher. Bi-2212 conductors have in fact been used to generate a 25 T field in a superconducting insert magnet. These two factors- the very high field critical current performance of Bi-2212, and the already demonstrated capability of this material for high field magnets up to 25 T, strongly suggest this material as a leading contender for the next generation high field superconducting (HFS) wire. This potential was recognized by the US Academy of Science's Committee on Opportunities in High Magnetic Field Science. Their report of the same name specifically calls out the high field potential for this material, and suggests that 30 T magnets appear feasible based on the performance of 2212. There are several requirements for HFS conductors. The most obvious is J{sub E} (B, T), the engineering current density at the field and temperature of operation. As shown in Fig. 1, Bi-2212 excels in this regard. Stability requirements for magnets dictate that the effective filament diameter should be less than 30 micrometers, something that Bi-2212 multifilamentary wire can uniquely satisfy among the HFS superconducting wire technologies. Additional requirements include mechanical properties that prevent stress limitation of J{sub E} at the operating conditions, resistive transition index (n-value) suffic
Bose Glass of Quasiparticles in Doped Quantum Magnet Gregory S. Boebinger, National High Magnetic Field Laboratory
Weston, Ken
Bose Glass of Quasiparticles in Doped Quantum Magnet Gregory S. Boebinger, National High Magnetic. This BEC can localize in the presence of disorder caused by Br- doping to form a Bose Glass. The BEC-Bose Glass (BEC-BG) transition can be carefully controlled by magnetic field, allowing us to sensitively
Cryogenic properties of dispersion strengthened copper for high magnetic fields
Toplosky, V. J.; Han, K.; Walsh, R. P. [National High Magnetic Field Laboratory, Tallahassee, FL 32310 (United States); Swenson, C. A. [Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States)
Cold deformed copper matrix composite conductors, developed for use in the 100 tesla multi-shot pulsed magnet at the National High Magnetic Field Laboratory (NHMFL), have been characterized. The conductors are alumina strengthened copper which is fabricated by cold drawing that introduces high dislocation densities and high internal stresses. Both alumina particles and high density of dislocations provide us with high tensile strength and fatigue endurance. The conductors also have high electrical conductivities because alumina has limited solubility in Cu and dislocations have little scattering effect on conduction electrons. Such a combination of high strength and high conductivity makes it an excellent candidate over other resistive magnet materials. Thus, characterization is carried out by tensile testing and fully reversible fatigue testing. In tensile tests, the material exceeds the design criteria parameters. In the fatigue tests, both the load and displacement were measured and used to control the amplitude of the tests to simulate the various loading conditions in the pulsed magnet which is operated at 77 K in a non-destructive mode. In order to properly simulate the pulsed magnet operation, strain-controlled tests were more suitable than load controlled tests. For the dispersion strengthened coppers, the strengthening mechanism of the aluminum oxide provided better tensile and fatigue properties over convention copper.
Towards Integrated Design and Modeling of High Field Accelerator Magnets
Caspi, S.; Ferracin, P.
The next generation of superconducting accelerator magnets will most likely use a brittle conductor (such as Nb{sub 3}Sn), generate fields around 18 T, handle forces that are 3-4 times higher than in the present LHC dipoles, and store energy that starts to make accelerator magnets look like fusion magnets. To meet the challenge and reduce the complexity, magnet design will have to be more innovative and better integrated. The recent design of several high field superconducting magnets have now benefited from the integration between CAD (e.g. ProE), magnetic analysis tools (e.g. TOSCA) and structural analysis tools (e.g. ANSYS). Not only it is now possible to address complex issues such as stress in magnet ends, but the analysis can be better detailed an extended into new areas previously too difficult to address. Integrated thermal, electrical and structural analysis can be followed from assembly and cool-down through excitation and quench propagation. In this paper we report on the integrated design approach, discuss analysis results and point out areas of future interest.
Apparatus for storing high magnetic fields having reduced mechanical forces and reduced magnetic pollution
Prueitt, M.L.; Mueller, F.M.; Smith, J.L.
The present invention identifies several configurations of conducting elements capable of storing extremely high magnetic fields for the purpose of energy storage or for other uses, wherein forces experienced by the conducting elements and the magnetic field pollution produced at locations away from the configuration are both significantly reduced over those which are present as a result of the generation of such high fields by currently proposed techniques. It is anticipated that the use of superconducting materials will both permit the attainment of such high fields and further permit such fields to be generated with vastly improved efficiency. 15 figures.
Apparatus for storing high magnetic fields having reduced mechanical forces and reduced magnetic pollution
Prueitt, Melvin L. (Los Alamos, NM); Mueller, Fred M. (Los Alamos, NM); Smith, James L. (Los Alamos, NM)
The present invention identifies several configurations of conducting elements capable of storing extremely high magnetic fields for the purpose of energy storage or for other uses, wherein forces experienced by the conducting elements and the magnetic field pollution produced at locations away from the configuration are both significantly reduced over those which are present as a result of the generation of such high fields by currently proposed techniques. It is anticipated that the use of superconducting materials will both permit the attainment of such high fields and further permit such fields to be generated with vastly improved efficiency.
Development of high temperature superconductors for magnetic field applications
Larbalestier, D.C.
The key requirement for magnetic field applications of high temperature superconductor (HTS) materials is to have conductors with high transport critical current density available for magnet builders. After 3 or 4 years of being without any such object, conductor makers have had recent success in producing simple conductor prototypes. These have permitted the construction of simple HTS magnets having self fields exceeding 1 tesla at 4K. Thus the scientific feasibility of making powerful HTS magnets has been demonstrated. Attention to the technological aspects of making HTS conductors for magnets with strong flux pinning and reduced superconducting granularity is now sensible and attractive. However, extrinsic defects such as filament sausaging, cracking, misaligned grains and other perturbation to long range current flow must be controlled at a low level if the benefit of intrinsic improvements to the critical current density is to be maintained in the conductor form. Due to the great complexity of the HTS materials, there is sometimes confusion as to whether a given sample has an intrinsically or extrinsically limited critical current density. Systematic microstructure variation experiments and resistive transition analysis are shown to be particularly helpful in this phase of conductor development.
The Superconducting Magnet Division at Brookhaven National Laboratory (BNL) has been carrying out design, engineering, and technology development of high performance magnets for future accelerators. High Temperature Superconductors (HTS) play a major role in the BNL vision of a few high performance interaction region (IR) magnets that would be placed in a machine about ten years from now. This paper presents the engineering design of a ''react and wind'' Nb{sub 3}Sn magnet that will provide a 12 Tesla background field on HTS coils. In addition, the coil production tooling as well as the most recent 10-turn R&D coil test results will be discussed.
Transmit field pattern control for high field magnetic resonance imaging with integrated RF current sourcesĀ
Kurpad, Krishna Nagaraj
The primary design criterion for RF transmit coils for MRI is uniform transverse magnetic (B1) field. Currently, most high frequency transmit coils are designed as periodic, symmetric structures that are resonant at the ...
Tuning magnetic disorder in diluted magnetic semiconductors using high fields to 89 Tesla
Crooker, Scott A [Los Alamos National Laboratory; Samarth, Nitin [PENN STATE U
We describe recent and ongoing studies at the National High Magnetic Field Laboratory at Los Alamos using the new '100 Tesla Multi-Shot Magnet', which is presently delivering fields up to {approx}89 T during its commissioning. We discuss the first experiments performed in this magnet system, wherein the linewidth of low-temperature photoluminescence spectra was used to directly reveal the degree of magnetic alloy disorder 'seen' by excitons in single Zn{sub 0.80}Cd{sub 0.22}Mn{sub 0.08}Se quantum wells. The magnetic potential landscape in II-VI diluted magnetic semiconductors (DMS) is typically smoothed when the embedded Mn{sup 2+} spins align in an applied field. However, an important (but heretofore untested) prediction of current models of compositional disorder is that magnetic alloy fluctuations in many DMS compounds should increase again in very large magnetic fields approaching 100 T. We observed precisely this increase above {approx}70 T, in agreement with a simple model of magnetic alloy disorder.
Conceptual Design of the 45 T Hybrid Magnet at the Nijmegen High Field Magnet Laboratory
Wiegers, SAJ; Bird, M D; Rook, J; Perenboom, J A A J; Wiegers, S A J; Bonito-Oliva, A; den Ouden, A
A 45 T Hybrid Magnet System is being developed at the Nijmegen High Field Magnet Laboratory as part of the Nijmegen Center for Advanced Spectroscopy. The 45 T Hybrid Magnet System will be used in combination with far-infra-red light produced by a Free Electron Laser under construction directly adjacent to the High Field Magnet Laboratory. The superconducting outsert magnet will consist of three CICC coils wound on a single coil form, using Nb3Sn strands. A test program for strand and cable qualification is underway. The CICC will carry 13 kA and the coils will produce 12 T on axis field in a 600 mm warm bore. The nominal operating temperature will be 4.5 K maintained with forced-flow supercritical helium. The insert magnet will produce 33 T at 40 kA in a 32 mm bore consuming 20 MW, and will consist of four coils. The insert magnet will be galvanically and mechanically isolated from the outsert magnet. Complete system availability for users is expected in 2014. In this paper we will report on the conceptual de...
Development of fast cooling pulsed magnets at the Wuhan National High Magnetic Field Center
Peng, Tao; Sun, Quqin; Zhao, Jianlong; Jiang, Fan; Li, Liang; Xu, Qiang [Wuhan National High Magnetic Field Center, Huazhong University of Science and Technology, Wuhan (China)] [Wuhan National High Magnetic Field Center, Huazhong University of Science and Technology, Wuhan (China); Herlach, Fritz [Department of Physics, Katholieke Universiteit Leuven, Celestijnenlaan 200D, B-3001 Leuven (Belgium)] [Department of Physics, Katholieke Universiteit Leuven, Celestijnenlaan 200D, B-3001 Leuven (Belgium)
Pulsed magnets with fast cooling channels have been developed at the Wuhan National High Magnetic Field Center. Between the inner and outer sections of a coil wound with a continuous length of CuNb wire, G10 rods with cross section 4 mm ū 5 mm were inserted as spacers around the entire circumference, parallel to the coil axis. The free space between adjacent rods is 6 mm. The liquid nitrogen flows freely in the channels between these rods, and in the direction perpendicular to the rods through grooves provided in the rods. For a typical 60 T pulsed magnetic field with pulse duration of 40 ms, the cooling time between subsequent pulses is reduced from 160 min to 35 min. Subsequently, the same technology was applied to a 50 T magnet with 300 ms pulse duration. The cooling time of this magnet was reduced from 480 min to 65 min.
High-field magnets using high-critical-temperature superconducting thin films
Mitlitsky, Fred (Livermore, CA); Hoard, Ronald W. (Livermore, CA)
High-field magnets fabricated from high-critical-temperature superconducting ceramic (HTSC) thin films which can generate fields greater than 4 Tesla. The high-field magnets are made of stackable disk-shaped substrates coated with HTSC thin films, and involves maximizing the critical current density, superconducting film thickness, number of superconducting layers per substrate, substrate diameter, and number of substrates while minimizing substrate thickness. The HTSC thin films are deposited on one or both sides of the substrates in a spiral configuration with variable line widths to increase the field.
High-field magnets using high-critical-temperature superconducting thin films
Mitlitsky, F.; Hoard, R.W.
High-field magnets fabricated from high-critical-temperature superconducting ceramic (HTSC) thin films which can generate fields greater than 4 Tesla are disclosed. The high-field magnets are made of stackable disk-shaped substrates coated with HTSC thin films, and involves maximizing the critical current density, superconducting film thickness, number of superconducting layers per substrate, substrate diameter, and number of substrates while minimizing substrate thickness. The HTSC thin films are deposited on one or both sides of the substrates in a spiral configuration with variable line widths to increase the field. 4 figures.
Coil Winding for the Series-Connected Hybrid Magnet Mark D. Bird, National High Magnetic Field Laboratory
Weston, Ken
Coil Winding for the Series-Connected Hybrid Magnet Mark D. Bird, National High Magnetic Field will produce for MagLab users magnetic fields of 36T featuring unprecedented (1ppm) homogeneity. Winding of the superconducting coil, the largest component of the magnet windings, is well underway. The superconducting coil
Spectral Mapping of Protein Torsion Angles National High Magnetic Field Laboratory
Weston, Ken
Spectral Mapping of Protein Torsion Angles National High Magnetic Field Laboratory NMR Spectroscopy spectra. #12;Spectral Mapping of Protein Torsion Angles National High Magnetic Field Laboratory NMR, in recording signals that are dependent on the orientation of the atoms with respect to the magnetic field, we
Use of High Magnetic Field to Control Microstructural Evolution in Metallic and Magnetic Materials
Ludtka, G.M.; Mackiewicz- Ludtka, G.; Wilgen, J.B.; Kisner, R.A.
The Amendment 1, referred to as Phase 2, to the original CRADA NFE-06-00414 added tasks 3 through 7 to the original statement of work that had two main tasks that were successfully accomplished in Phase 1 of this project. In this Phase 2 CRADA extension, extensive research and development activities were conducted using high magnetic field processing effects for the purpose of manipulating microstructure in the SAE 5160 steel to refine grain size isothermally and to develop nanocrystalline spacing pearlite during continuous cooling, and to enhance the formability/forgability of the non-ferrous precipitation hardening magnesium alloy AZ90 by applying a high magnetic field during deformation processing to investigate potential magnetoplasticity in this material. Significant experimental issues (especially non-isothermal conditions evolving upon insertion of an isothermal sample in the high magnetic field) were encountered in the isothermal phase transformation reversal experiments (Task 4) that later were determined to be due to various condensed matter physics phenomenon such as the magnetocaloric (MCE) effect that occurs in the vicinity of a materials Curie temperature. Similarly the experimental deformation rig had components for monitoring deformation/strain (Task 3) that were susceptible to the high magnetic field of the ORNL Thermomagnetic Processing facility 9-T superconducting magnet that caused electronic components to fail or record erroneous (very noisy) signals. Limited experiments on developing nanocrystalline spacing pearlite were not sufficient to elucidate the impact of high magnetic field processing on the final pearlite spacing since significant statistical evaluation of many pearlite colonies would need to be done to be conclusive. Since extensive effort was devoted to resolving issues for Tasks 3 and 7, only results for these focused activities are included in this final CRADA report along with those for Task 7 (described in the Objectives Section of this report).
High pressure apparatus for transport properties study in high magnetic field
Alsmadi, A. M. (Abdel M.); Nakotte, H. (Heinrich); Honda, F.; Sechovsky, V. (Vladimir); Mikulina, O. (Olga); Kamarad, J.; Lacerda, A. H. (Alex H.)
We have designed a high pressure apparatus for measuring electrical-transport properties at low temperatures, high magnetic field and hydrostatic pressure up to 10 kbar. Details of the high-pressure cell and an exemplary study on UNiAI are described and discussed briefly.
Compressing magnetic fields with high-energy lasersa... J. P. Knauer,1,b
Compressing magnetic fields with high-energy lasersa... J. P. Knauer,1,b O. V. Gotchev,1,2,3 P. Y, Rochester, New York 14623, USA 3 Department of Mechanical Engineering, University of Rochester, 250 East-driven magnetic-field compression producing a magnetic field of tens of megaGauss is reported for the first time
Weston, Ken
, recognized as the world leader in magnet science, engineering, and experimental infrastructureNATIONAL HIGH MAGNETIC FIELD LABORATORY REPORTSVOLUME 11 Ę N0.2 Ę 2004 OPERATED BY: FLORIDA STATE: National High Magnetic Field Laboratory 1800 East Paul Dirac Drive Tallahassee, Florida 32310-3706 Tel: 850
The influence of a magnetic field on turbulent heat transfer of a high Prandtl number fluid
Nakaharai, H. [Department of Advanced Energy Engineering Science, Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, Kasuga-kouen 6-1, Kasuga, Fukuoka 816-8580 (Japan); Takeuchi, J.; Morley, N.B.; Abdou, M.A. [Mechanical and Aerospace Engineering Department, University of California, Los Angeles, CA 90095-1597 (United States); Yokomine, T. [Faculty of Energy Engineering Science, Kyushu University, Kasuga-kouen 6-1, Kasuga, Fukuoka 816-8580 (Japan); Kunugi, T. [Department of Nuclear Engineering, Kyoto University, Yoshida, Sakyo, Kyoto 606-8501 (Japan); Satake, S. [Department of Applied Electronics, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510 (Japan)
The influence of a transverse magnetic field on the local and average heat transfer of an electrically conducting, turbulent fluid flow with high Prandtl number was studied experimentally. The mechanism of heat transfer modification due to magnetic field is considered with aid of available numerical simulation data for turbulent flow field. The influence of the transverse magnetic field on the heat transfer was to suppress the temperature fluctuation and to steepen the mean temperature gradient in near-wall region in the direction parallel to the magnetic field. The mean temperature gradient is not influenced compared to the temperature fluctuation in the direction vertical to the magnetic field. (author)
Weston, Ken
NATIONAL HIGH MAGNETIC FIELD LABORATORY REPORTSSPRING EDITION VOLUME 13 Ę N0. 2 Ę 2006 SUPPORTED BY OF FLORIDA Ę LOS ALAMOS NATIONAL LABORATORY Pulsed Field Facility: Heat caPacity in tHe 20 t dilution ReFRigeRatoR tRiPle Resonance PRobe #12;NHMFLREPORTS C O N T E N T S Published by: National High Magnetic Field
Weston, Ken
Weston, Ken
, and Geochemistry 16 MAGNET SCIENCE & TECHNOLOGY Engineering Materials, Instrumentation, and Magnet Technology 20NATIONAL HIGH MAGNETIC FIELD LABORATORY REPORTSSPECIAL EDITION VOLUME 13 Ę N0. 1 Ę 2006 SUPPORTED HIGHLIGHTS FROM Life Sciences Chemistry Magnet Science & Technology Condensed Matter Page 15 #12;NHMFLREPORTS
High Field Magnetization measurements of uranium dioxide single crystals (P08358- E003-PF)
K. Gofryk; N. Harrison; M. Jaime
Conclusions: Our preliminary high field magnetic measurements of UO2 are consistent with a complex nature of the magnetic ordering in this material, compatible with the previously proposed non-collinear 3-k magnetic structure. Further extensive magnetic studies on well-oriented (<100 > and <111>) UO2 crystals are planned to address the puzzling behavior of UO2 in both antiferromagnetic and paramagnetic states at high fields.
Weston, Ken
UPPort scientists neWs FroM tHe dc FieLd FaciLitY: QUantUM HaLL eFFect in graPHene at HigH Magnetic FieLds ed NEARING COMPLETION 14 NEWS FROM THE DC FIELD FACILITY QuantuM Hall effect In grapHene at HIgH MagnetIc f
Helium gas bubble trapped in liquid helium in high magnetic field
Bai, H., E-mail: email@example.com; Hannahs, S. T.; Markiewicz, W. D.; Weijers, H. W. [National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310 (United States)
High magnetic field magnets are used widely in the area of the condensed matter physics, material science, chemistry, geochemistry, and biology at the National High Magnetic Field Laboratory. New high field magnets of state-of-the-art are being pursued and developed at the lab, such as the current developing 32?T, 32?mm bore fully superconducting magnet. Liquid Helium (LHe) is used as the coolant for superconducting magnets or samples tested in a high magnetic field. When the magnetic field reaches a relatively high value the boil-off helium gas bubble generated by heat losses in the cryostat can be trapped in the LHe bath in the region where BzdBz/dz is less than negative 2100 T{sup 2}/m, instead of floating up to the top of LHe. Then the magnet or sample in the trapped bubble region may lose efficient cooling. In the development of the 32?T magnet, a prototype Yttrium Barium Copper Oxide coil of 6 double pancakes with an inner diameter of 40?mm and an outer diameter of 140?mm was fabricated and tested in a resistive magnet providing a background field of 15?T. The trapped gas bubble was observed in the tests when the prototype coil was ramped up to 7.5?T at a current of 200?A. This letter reports the test results on the trapped gas bubble and the comparison with the analytical results which shows they are in a good agreement.
Nanoscale Diffusion Studies of Lipid Membranes National High Magnetic Field Laboratory
Weston, Ken
Magnetic Resonance Imaging & Spectroscopy User Facility, University of Florida Chemical Engineering We haveNanoscale Diffusion Studies of Lipid Membranes National High Magnetic Field Laboratory Advanced for the facility's future use. This will serve to enhance infrastructure for research and education at the Magnet
SUMMERVOLUME 14 No.31 SUMMER 2007 VOLUME 14 NO. 3 NATIONAL HIGH MAGNETIC FIELD LABORATORY
Weston, Ken
a team of engineers capable of pushing magnetic fields to new highs? you already know the answer to announce that a key person who helped lead the magnet engineering team to world prominence no longer has of the Magnet Science & Technology group, as well as its chief engineer. In addition to keeping many balls
High Performance Superconducting Wire in High Applied Magnetic Fields via Nanoscale Defect Engineering
Goyal, Amit [ORNL; Wee, Sung Hun [ORNL; Zuev, Yuri L [ORNL; Cantoni, Claudia [ORNL
High temperature superconducting (HTS) wires capable of carrying large critical currents with low dissipation levels in high applied magnetic fields are needed for a wide range of applications. In particular, for electric power applications involving rotating machinery, such as large-scale motors and generators, a high critical current, Ic, and a high engineering critical current density, JE, in applied magnetic fields in the range of 3 5 Tesla (T) at 65 K are required. In addition, exceeding the minimum performance requirements needed for these applications results in a lower fabrication cost, which is regarded as crucial to realize or enable many large-scale bulk applications of HTS materials. Here we report the fabrication of short segments of a potential superconducting wire comprised of a 4 m thick YBa2Cu3O7? (YBCO) layer on a biaxially textured substrate with a 50% higher Ic and JE than the highest values reported previously. The YBCO film contained columns of self-assembled nanodots of BaZrO3 (BZO) roughly oriented along the c-axis of YBCO. Although the YBCO film was grown at a high deposition rate, three-dimensional self-assembly of the insulating BZO nanodots still occurred. For all magnetic field orientations, minimum Ic and JE at 65 K, 3 T for the wire were 353 A cm?1 and 65.4 kA cm?2, respectively.
NHMFL Breaks the 100 Tesla Barrier Gregory S. Boebinger, National High Magnetic Field Laboratory
Weston, Ken
NHMFL Breaks the 100 Tesla Barrier Gregory S. Boebinger, National High Magnetic Field Laboratory. 109no. 31 12404-12407 On March 22nd 2012, the NHMFL ┬Ł Pulsed Field Facility broke the 100T tesla barrier, setting a world record of 100.75 tesla for a non-destructive magnet. By using advanced
A field-reversed magnetic configuration and applications of high-temperature FRC plasma
Ryzhkov, S. V., E-mail: email@example.com [Bauman Moscow State Technical University (Russian Federation)
As applied to a tokomak, a magnetic trap for confinement of a plasma with an inverted field or a magnetic field reversed configuration (FRC) is one of the most promising alternatives of the systems with high {beta}. A brief review of the latest data on FRC and potential directions of using such configurations in addition to energy generation in thermonuclear reactors (TNRs) is proposed.
High-Efficiency Plasma Refuelling by Pellet Injection from the Magnetic High-Field Side into ASDEX Upgrade
Lang, P.T.; Buechl, K.; Kaufmann, M.; Lang, R.S.; Mertens, V.; Mueller, H.W.; Neuhauser, J. [Max-Planck-Institut fuer Plasmaphysik, EURATOM-IPP Association, Garching (Germany)] [Max-Planck-Institut fuer Plasmaphysik, EURATOM-IPP Association, Garching (Germany); ASDEX Upgrade% NI Teams
High-efficiency refuelling of ELMy {ital H}-mode tokamak discharges with solid deuterium pellets injected from the magnetic high-field side is demonstrated. Compared to standard low-field side injection, the fuelling efficiency was enhanced by a factor of 4, the pellet penetration more than 2 times. This experimental result can be qualitatively explained by the magnetic force pushing a diamagnetic plasma cloud towards lower magnetic field, causing rapid particle loss for shallow low-field side injection, but enhancing fuelling efficiency and pellet penetration for high-field side injection. {copyright} {ital 1997} {ital The American Physical Society}
High Field Magnet R&D in the USA
Gourlay, S.A.
beam instmmentation, accelerator physics shIdies, and designShldy in terms of accelerator physics and magnet design.magnet technology and accelerator physics and approach the
Ultra-High Intensity Magnetic Field Generation in Dense Plasma
Fisch, Nathaniel J
I. Grant Objective The main objective of this grant proposal was to explore the efficient generation of intense currents. Whereasthefficient generation of electric current in low-Ł?energy-Ł? density plasma has occupied the attention of the magnetic fusion community for several decades, scant attention has been paid to carrying over to high-Ł?energy-Ł? density plasma the ideas for steady-Ł?state current drive developed for low-Ł?energy-Ł? density plasma, or, for that matter, to inventing new methodologies for generating electric current in high-Ł?energy-Ł?density plasma. What we proposed to do was to identify new mechanisms to accomplish current generation, and to assess the operation, physics, and engineering basis of new forms of current drive in regimes appropriate for new fusion concepts.
New High Field Magnet for Neutron Scattering at Hahn-Meitner Institute
M Steiner; D A Tennant; P Smeibidl
Abstract. The Berlin Neutron Scattering Center BENSC at the Hahn-Meitner-Institute (HMI) is a user facility for the study of structure and dynamics of condensed matter with neutrons and synchrotron radiation with special emphasis on experiments under extreme conditions. Neutron scattering is uniquely suited to study magnetic properties on a microscopic length scale, because neutrons have comparable wavelengths and, due to their magnetic moment, they interact with the atomic magnetic moments. Magnetic interactions and magnetic phenomena depend on thermodynamic parameters like magnetic field, temperature and pressure. At HMI special efforts are being made to offer outstanding sample environments such as very low temperatures or high magnetic fields or combination of both. For the future a dedicated instrument for neutron scattering at extreme fields is under construction, the Extreme Environment Diffractometer ExED. For this instrument the existing superconducting magnets as well as a future hybrid system can be used. The highest fields, above 30 T will be produced by the planned series-connected hybrid magnet system, designed and constructed in collaboration with the National High Magnetic Field Laboratory, Tallahassee, FL. 1.
Presented by the National High Magnetic Field Laboratory
Weston, Ken
! Cooling holes on the Bitter plates let cold water run through the magnet so it doesn't get too hot. l magnets found in houses. The answers will fit into the crossword puzzle below. ACROSS Where you store milk
Coexisting Superconductivity and Magnetism in UCoGe Gregory S. Boebinger, National High Magnetic Field Laboratory
Weston, Ken
Coexisting Superconductivity and Magnetism in UCoGe Gregory S. Boebinger, National High Magnetic focused on the coexistence of superconductivity and ferromagnetism, including UGe2, URhGe, and UCoGe. In these materials, superconductivity develops below the ferromagnetic Curie temperature TC without destroying
Instrumentation for Measurement of Strain Dependence of Nb3Sn Conductors National High Magnetic Field Laboratory
Weston, Ken
Instrumentation for Measurement of Strain Dependence of Nb3Sn Conductors National High Magnetic Field Laboratory Magnet Science and Technology, Florida State University An NHMFL User Collaboration Grants Program (UCGP) award is supporting students from the FAMU-FSU College of Engineering as part
Influence of high magnetic field on the luminescence of Eu{sup 3+}-doped glass ceramics
Jiang, Wei; Chen, Weibo; Chen, Ping; Xu, Beibei; Zheng, Shuhong; Guo, Qiangbing; Liu, Xiaofeng, E-mail: email@example.com, E-mail: firstname.lastname@example.com [State Key Laboratory of Silicon Materials, Department of Materials Science and Engineering, Zhejiang University, Hangzhou, Zhejiang 310027 (China); Zhang, Junpei; Han, Junbo [Wuhan National High Magnetic field Center, Huazhong University of Science and Technology, Wuhan, Hubei 430074 (China); Qiu, Jianrong, E-mail: email@example.com, E-mail: email@example.com [State Key Laboratory of Silicon Materials, Department of Materials Science and Engineering, Zhejiang University, Hangzhou, Zhejiang 310027 (China); State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou, Guangdong 510640 (China)
Rare earth (RE) doped materials have been widely exploited as the intriguing electronic configuration of RE ions offers diverse functionalities from optics to magnetism. However, the coupling of magnetism with photoluminescence (PL) in such materials has been rarely reported in spite of its fundamental significance. In the present paper, the effect of high pulsed magnetic field on the photoluminescence intensity of Eu{sup 3+}-doped nano-glass-ceramics has been investigated. In our experiment, Eu-doped oxyfluoride glass and glass ceramic were prepared by the conventional melt-quenching process and controlled heat treatment. The results demonstrate that the integrated PL intensity of Eu{sup 3+} decreases with the enhancement of magnetic field, which can be interpreted in terms of cooperation effect of Zeeman splitting and magnetic field induced change in site symmetry. Furthermore, as a result of Zeeman splitting, both blue and red shift in the emission peaks of Eu{sup 3+} can be observed, and this effect becomes more prominent with the increase of magnetic field. Possible mechanisms associated with the observed magneto-optical behaviors are suggested. The results of the present paper may open a new gate for modulation of luminescence by magnetic field and remote optical detection of magnetic field.
Stable High Beta Plasmas Confined by a Dipole Magnetic Field D. T. Garnier,
Mauel, Michael E.
Stable High Beta Plasmas Confined by a Dipole Magnetic Field D. T. Garnier, A. Hansen, M. E. Mauel Center, MIT, Cambridge, MA 02139 (Dated: October 21, 2005) Abstract Stable high-beta plasma is created we report the first production of high beta plasma confined by a laboratory dipole using neutral gas
Phase transitions in Dual-Gated Bilayer Graphene Gregory S. Boebinger, National High Magnetic Field Laboratory
Weston, Ken
Phase transitions in Dual-Gated Bilayer Graphene Gregory S. Boebinger, National High Magnetic Field Laboratory DMR-Award 0654118 DC Field Facility Bilayer graphene, consisting of two layers of carbon atoms of the degeneracy of the electronic states in the graphene bilayer. Resistivity plotted as a function of the front
Fermi Surface of Uranium at Ambient Pressure Gregory S. Boebinger, National High Magnetic Field Laboratory
Weston, Ken
Fermi Surface of ŁUranium at Ambient Pressure Gregory S. Boebinger, National High Magnetic Field Laboratory DMR-Award 0654118 DC Field Facility User Program The fermi surface of ŁUranium has been measured surface of alpha-uranium at ambient pressure, Phys. Rev. B Rapid Commun., 80, 241101 (2009). B//c-axis B
Beuther, H. [Max-Planck-Institute for Astronomy, Koenigstuhl 17, 69117 Heidelberg (Germany); Vlemmings, W. H. T. [Argelander Institute for Astronomy, University of Bonn, Auf dem Huegel 71, 53121 Bonn (Germany); Rao, R. [Academia Sinica, Institute of Astronomy and Astrophysics, Taipei, Taiwan (China); Van der Tak, F. F. S., E-mail: firstname.lastname@example.com, E-mail: firstname.lastname@example.com, E-mail: email@example.com, E-mail: email@example.com [SRON Netherlands Institute for Space Research, Landleven 12, 9747 AD Groningen (Netherlands)
To characterize the magnetic field structure of the outflow and core region within a prototypical high-mass star-forming region, we analyzed polarized CO(3-2)-for the first time observed with the Submillimeter Array-as well as 880 {mu}m submillimeter continuum emission from the high-mass outflow/disk system IRAS 18089-1732. Both emission features with polarization degrees at a few percent level indicate that the magnetic field structure is largely aligned with the outflow/jet orientation from small core scales to larger outflow scales. Although quantitative estimates are crude, the analysis indicates that turbulent energy dominates over magnetic energy. The data also suggest a magnetic field strength increase from the lower-density envelope to the higher-density core.
Reply to "Comment on `Microwave vortex dissipation of superconducting Nd-Ce-Cu-O epitaxial films in high magnetic fields' "
Yeh, Nai-Chang
in high magnetic fields' " N.-C. Yeh1 and D. M. Strayer2 1Department of Physics, California Institute of Technology, Pasadena, California 91125, USA 2 Jet Propulsion Laboratory, California Institute of Technology of these modes are insensitive to the application of external magnetic fields, be- cause magnetic fields do
The National High Magnetic Field Laboratory was represented by staff from its Center for Integrating Research and Learning
McQuade, D. Tyler
to drop a magnet seemingly in slow motion through a copper pipe. The USA Science and Engineering Festival and Engineering Festival National High Magnetic Field Laboratory Funding Grants: G.S. Boebinger (NSF DMR-1157490The National High Magnetic Field Laboratory was represented by staff from its Center
9 T high magnetic field annealing effects on FeN bulk sample
Jiang, Yanfeng; Wang, Jian-Ping, E-mail: firstname.lastname@example.com [Department of Electrical and Computer Engineering, University of Minnesota, Minneapolis, Minneota 55455 (United States); Dabade, Vivekanand; James, Richard D. [Department of Aerospace Engineering and Mechanics, University of Minnesota, Minneapolis, Minnesota 55455 (United States); Brady, Michael P.; Rios, Orlando [Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831¢6115 (United States)
??-Fe{sub 16}N{sub 2} has been suggested as a promising candidate for future rare-earth-free magnets. In this paper, we report to use high magnetic field (9?T) assisted post-annealing process to enhance the Fe{sub 16}N{sub 2} phase formation in FeN bulk rod samples during the ?? ? ?? phase transformation and thus improve its magnetic properties. It was found by X-ray Diffraction measurement that the volume ratio of Fe{sub 16}N{sub 2} phase was increased up to 22%, which corresponds to an increase in the amount of transformation from ?? ? ?? up to 78%. Also, the saturation magnetization (M{sub s}) of the prepared FeN rod sample was increased to 227?emu/g with its coercivity up to 376?Oe at room temperature. A working mechanism for the high field assisted post-annealing process was presented.
The Curie-Weiss constant of solid 3He on the melting curve at high magnetic fields
Paris-Sud XI, Universit├® de
magnetic fields. A plastic Pomeranchuk cell [9] was precooled down to 3 mK by a dilution refrigerator [10JL-625 The Curie-Weiss constant of solid 3He on the melting curve at high magnetic fields H. Godfrin by NMR at high magnetic fields (7.2 teslas). The result (03B8 ~ - 3 mK) is in agreement with low field
High Magnetic Field Multipoles Generated by Superconductor Magnetization within a Set of Nested Superconducting Correction Coils
Green, M.A.
magnetization of the superconductor in the long correctorsMultipoles Generated by Superconductor Magnetization WithinMULTIPOLES GENERATED BY SUPERCONDUCTOR MAGNETIZATION WITHIN
Symmetry Breaking in Graphene Gregory S. Boebinger, National High Magnetic Field Laboratory
Weston, Ken
Symmetry Breaking in Graphene Gregory S. Boebinger, National High Magnetic Field Laboratory DMR. In this experiment, Landau levels in graphene were used to study the breaking of SU(4) symmetry--a higher dimensional states by their spin polarization. It was found that graphene turns into either a spin ferromagnet
Proton Transport by the Influenza M2 Protein Gregory S. Boebinger, National High Magnetic Field Laboratory
Weston, Ken
Proton Transport by the Influenza M2 Protein Gregory S. Boebinger, National High Magnetic Field infections) in native like lipid bilayers has allowed us to determine a novel mechanism for proton transport that has not been observed in any other protein. At the heart of this proton channel is a set of 4
FURMAN NMR SAFETY INFORMATION Standard safety guidelines have been put in place for work around the high-field magnets, and all users
Earth's magnetic field 6.0 x 10-5 T at the equator Refrigerator Magnet .0100-.0150 T MRI Medical the high-field magnets, and all users must take proper precautions to prevent expensive instrument damage and serious personal injury, including death. NMR Magnetic Field Strength Ę Remember: The magnetic field
Far-infrared properties of superconducting YBa2Cu3O7-d films in high magnetic fields
Tanner, David B.
Far-infrared properties of superconducting YBa2Cu3O7-d films in high magnetic fields H.L. Liua,*, A of Physics, University of Florida, Gainesville, FL 32611, USA b National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32306, USA c Jet Propulsion Laboratory, California Institute
A Sliding Ring Coil for Neuroimaging at 21.1 T Gregory S. Boebinger, National High Magnetic Field Laboratory
Weston, Ken
A Sliding Ring Coil for Neuroimaging at 21.1 T Gregory S. Boebinger, National High Magnetic Field interference; and 4. anesthesia & vacuum lines for animal care. #12;A Sliding Ring Coil for Neuroimaging at 21 sliding tuner ring for neuroimaging in high field vertical magnets: Ex and in vivo applications at 21.1 T
High-precision description and new properties of a spin-1 particle in a magnetic field
Alexander J. Silenko
The exact Foldy-Wouthuysen Hamiltonian is derived for a pointlike spin-1 particle with a normal magnetic moment in a nonuniform magnetic field. For a uniform magnetic field, it is exactly separated into terms linear and quadratic in spin. New unexpected properties of a particle with an anomalous magnetic moment are found. Spin projections of a particle moving in a uniform magnetic field are not integer and the tensor polarization is asymmetric in the plane orthogonal to the field. Previously described spin-tensor effects caused by the tensor magnetic polarizability exist not only for nuclei but also for pointlike particles.
The Cyclotron Fundamental Exposed in the High-Field Magnetic Variable V884 Her
G. D. Schmidt; L. Ferrario; D. T. Wickramasinghe; P. S. Smith
High-quality phase-resolved optical spectropolarimetry is presented for the magnetic cataclysmic variable V884 Her. The overall circular polarization during active accretion states is low and only slightly variable in the range 5000-8000A. However, the polarization is highly structured with wavelength, showing very broad polarization humps, narrow features that are associated with weak absorption lines in the total spectral flux, and sharp reversals across each major emission line. The polarization reversals arise from Zeeman splitting in the funnel gas in a longitudinal magnetic field B~30kG. The set of narrow, polarized absorption features matches the Zeeman pattern of hydrogen for a nearly uniform magnetic field of B=150MG, indicating that the features are "halo" absorption lines formed in a relatively cool reversing layer above the shock. With this identification, the broad polarization humps centered near 7150A and below 4000A are assigned to cyclotron emission from the fundamental and first harmonic (n=2), respectively. V884 Her is only the second AM Her system known with a field exceeding 100MG, and the first case in which the cyclotron fundamental has been directly observed from a magnetic white dwarf.
Cost Effective Open Geometry HTS MRI System amended to BSCCO 2212 Wire for High Field Magnets
Kennth Marken
The original goal of this Phase II Superconductivity Partnership Initiative project was to build and operate a prototype Magnetic Resonance Imaging (MRI) system using high temperature superconductor (HTS) coils wound from continuously processed dip-coated BSCCO 2212 tape conductor. Using dip-coated tape, the plan was for MRI magnet coils to be wound to fit an established commercial open geometry, 0.2 Tesla permanent magnet system. New electronics and imaging software for a prototype higher field superconducting system would have added significantly to the cost. However, the use of the 0.2 T platform would allow the technical feasibility and the cost issues for HTS systems to be fully established. Also it would establish the energy efficiency and savings of HTS open MRI compared with resistive and permanent magnet systems. The commercial goal was an open geometry HTS MRI running at 0.5 T and 20 K. This low field open magnet was using resistive normal metal conductor and its heat loss was rather high around 15 kolwatts. It was expected that an HTS magnet would dissipate around 1 watt, significantly reduce power consumption. The SPI team assembled to achieve this goal was led by Oxford Instruments, Superconducting Technology (OST), who developed the method of producing commercial dip coated tape. Superconductive Components Inc. (SCI), a leading US supplier of HTS powders, supported the conductor optimization through powder optimization, scaling, and cost reduction. Oxford Magnet Technology (OMT), a joint venture between Oxford Instruments and Siemens and the worldÆs leading supplier of MRI magnet systems, was involved to design and build the HTS MRI magnet and cryogenics. Siemens Magnetic Resonance Division, a leading developer and supplier of complete MRI imaging systems, was expected to integrate the final system and perform imaging trials. The original MRI demonstration project was ended in July 2004 by mutual consent of Oxford Instruments and Siemens. Between the project start and that date a substantial shift in the MRI marketplace occurred, with rapid growth for systems at higher fields (1.5 T and above) and a consequent decline in the low field market (<1.0 T). While the project aim appeared technically attainable at that time, the conclusion was reached that the system and market economics do not warrant additional investment. The program was redirected to develop BSCCO 2212 multifilament wire development for high field superconducting magnets for NMR and other scientific research upon an agreement between DOE and Oxford Instruments, Superconducting Technology. The work t took place between September, 2004 and the project end in early 2006 was focused on 2212 multifilamentary wire. This report summarizes the technical achievements both in 2212 dip coated for an HTS MRI system and in BSCCO 2212 multifilamentary wire for high field magnets.
Thermal and high magnetic field treatment of materials and associated apparatus
Kisner, Roger A.; Wilgen, John B.; Ludtka, Gerard M.; Jaramillo, Roger A.; Mackiewicz-Ludtka, Gail
An apparatus and method for altering characteristics, such as can include structural, magnetic, electrical, optical or acoustical characteristics, of an electrically-conductive workpiece utilizes a magnetic field within which the workpiece is positionable and schemes for thermally treating the workpiece by heating or cooling techniques in conjunction with the generated magnetic field so that the characteristics of the workpiece are effected by both the generated magnetic field and the thermal treatment of the workpiece.
Thermal and high magnetic field treatment of materials and associated apparatus
Kisner, Roger A.; Wilgen, John B.; Ludtka, Gerard M.; Jaramillo, Roger A.; Mackiewicz-Ludtka, Gail
An apparatus and method for altering characteristics, such as can include structural, magnetic, electrical, optical or acoustical characteristics, of an electrically-conductive workpiece utilizes a magnetic field within which the workpiece is positionable and schemes for thermally treating the workpiece by heating or cooling techniques in conjunction with the generated magnetic field so that the characteristics of the workpiece are effected by both the generated magnetic field and the thermal treatment of the workpiece.
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Weston, Ken
related research in all areas of science and engineering.The Magnet Lab is supported by the National1 a publication of the National High Magnetic Field Laboratory1111111 a pa pa pa pa pa pa magnet lab packs a big punch. InThisIssue VOLUME 3: ISSUE 2 F E A T U R E S Flux is a twice
Fast magnetic field annihilation in the relativistic collisionless regime driven by two ultra-short high-intensity laser pulses
Gu, Y J; Kumar, D; Liu, Y; Singh, S K; Esirkepov, T Zh; Bulanov, S V; Weber, S; Korn, G
The magnetic quadrupole structure formation during the interaction of two ultra-short high power laser pulses with a collisionless plasma is demonstrated with 2.5-dimensional particle-in-cell simulations. The subsequent expansion of the quadrupole is accompanied by magnetic field annihilation in the ultrarelativistic regime, when the magnetic field can not be sustained by the plasma current. This results in a dominant contribution of the displacement current exciting a strong large scale electric?field. This field leads to the conversion of magnetic energy into kinetic energy of accelerated electrons inside the thin current sheet.
Shrink Tube Insulation Apparatus for Rebco Superconducting Tapes for Use in High Field Magnets
Whittington, Andrew
An increasing number of applications require the use of high temperature superconductors (HTS) such as (RE=Rare Earth) Ba2Cu3O7-x (REBCO) coated conductors [1]. HTS conductors show particularly great potential for high field magnets applications [1] due to their high upper critical fields [2], But several groups have shown that REBCO coated conductors are prone to delamination failure [3] [4] [5]. Under relatively low transverse stress the HTS film separates from the substrate and the conductor degrades [6]. This is problematic due to high transverse stresses that occur in fully epoxy impregnated solenoids wound with this conductor. Application of thin walled heat shrink tubing introduces a weak plane around the conductor, preventing delamination degradation [7]. However, manual application of the shrink tubing is impractical, requiring three operators limited to insulating 100 m lengths or less of REBCO conductor. The high risk of damage to the conductor, also associated with this process, shows the need for...
New vertical cryostat for the high field superconducting magnet test station at CERN
Vande Craen, A.; Atieh, S.; Bajko, M.; Benda, V.; Rijk, G. de; Favre, G.; Giloux, C.; Minginette, P.; Parma, V.; Perret, P.; Pirotte, O.; Ramos, D.; Viret, P. [CERN European Organization for Nuclear Research, Meyrin 1211, Geneva 23, CH (Switzerland); Hanzelka, P. [Institute of Scientific Instruments of the ASCR, Kralovopolska 147, 612 64 Brno, CZ (Czech Republic)
In the framework of the R and D program for new superconducting magnets for the Large Hadron Collider accelerator upgrades, CERN is building a new vertical test station to test high field superconducting magnets of unprecedented large size. This facility will allow testing of magnets by vertical insertion in a pressurized liquid helium bath, cooled to a controlled temperature between 4.2 K and 1.9 K. The dimensions of the cryostat will allow testing magnets of up to 2.5 m in length with a maximum diameter of 1.5 m and a mass of 15 tons. To allow for a faster insertion and removal of the magnets and reducing the risk of helium leaks, all cryogenics supply lines are foreseen to remain permanently connected to the cryostat. A specifically designed 100 W heat exchanger is integrated in the cryostat helium vessel for a controlled cooling of the magnet from 4.2 K down to 1.9 K in a 3 m{sup 3} helium bath. This paper describes the cryostat and its main functions, focusing on features specifically developed for this project. The status of the construction and the plans for assembly and installation at CERN are also presented.
AC transport in p-Ge/GeSi quantum well in high magnetic fields
Drichko, I. L.; Malysh, V. A.; Smirnov, I. Yu.; Golub, L. E.; Tarasenko, S. A. [A.F. Ioffe Physical Technical Institute of Russian Academy of Sciences, 194021 St. Petersburg (Russian Federation); Suslov, A. V. [National High Magnetic Field Laboratory, Tallahassee, FL 32310 (United States); Mironov, O. A. [Warwick SEMINANO R and D Center, University of Warwick Science Park, Coventry CV4 7EZ (United Kingdom); Kummer, M.; Kõnel, H. von [Laboratorium f³r Festk÷rperphysik ETH Z³rich, CH-8093 Z³rich (Switzerland)
The contactless surface acoustic wave technique is implemented to probe the high-frequency conductivity of a high-mobility p-Ge/GeSi quantum well structure in the regime of integer quantum Hall effect (IQHE) at temperatures 0.3¢5.8 K and magnetic fields up to 18 T. It is shown that, in the IQHE regime at the minima of conductivity, holes are localized and ac conductivity is of hopping nature and can be described within the ōtwo-siteö model. The analysis of the temperature and magnetic-field-orientation dependence of the ac conductivity at odd filing factors enables us to determine the effective hole g-factor, |g{sub zz}|?4.5. It is shown that the in-plane component of the magnetic field leads to a decrease in the g-factor as well as increase in the cyclotron mass, which is explained by orbital effects in the complex valence band of germanium.
Polarization-preserving confocal microscope for optical experiments in a dilution refrigerator with high magnetic field
Maksym Sladkov; M. P. Bakker; A. U. Chaubal; D. Reuter; A. D. Wieck; C. H. van der Wal
We present the design and operation of a fiber-based cryogenic confocal microscope. It is designed as a compact cold-finger that fits inside the bore of a superconducting magnet, and which is a modular unit that can be easily swapped between use in a dilution refrigerator and other cryostats. We aimed at application in quantum optical experiments with electron spins in semiconductors and the design has been optimized for driving with, and detection of optical fields with well-defined polarizations. This was implemented with optical access via a polarization maintaining fiber together with Voigt geometry at the cold finger, which circumvents Faraday rotations in the optical components in high magnetic fields. Our unit is versatile for use in experiments that measure photoluminescence, reflection, or transmission, as we demonstrate with a quantum optical experiment with an ensemble of donor-bound electrons in a thin GaAs film.
Polarization-preserving confocal microscope for optical experiments in a dilution refrigerator with high magnetic field
Sladkov, Maksym; Chaubal, A U; Reuter, D; Wieck, A D; van der Wal, C H
We present the design and operation of a fiber-based cryogenic confocal microscope. It is designed as a compact cold-finger that fits inside the bore of a superconducting magnet, and which is a modular unit that can be easily swapped between use in a dilution refrigerator and other cryostats. We aimed at application in quantum optical experiments with electron spins in semiconductors and the design has been optimized for driving with, and detection of optical fields with well-defined polarizations. This was implemented with optical access via a polarization maintaining fiber together with Voigt geometry at the cold finger, which circumvents Faraday rotations in the optical components in high magnetic fields. Our unit is versatile for use in experiments that measure photoluminescence, reflection, or transmission, as we demonstrate with a quantum optical experiment with an ensemble of donor-bound electrons in a thin GaAs film.
A table-top, repetitive pulsed magnet for nonlinear and ultrafast spectroscopy in high magnetic fields up to 30 T
Noe, G. Timothy; Lee, Joseph; Woods, Gary L. [Department of Electrical and Computer Engineering, Rice University, Houston, Texas 77005 (United States)] [Department of Electrical and Computer Engineering, Rice University, Houston, Texas 77005 (United States); Nojiri, Hiroyuki [Institute for Materials Research, Tohoku University, Sendai 980-8577 (Japan)] [Institute for Materials Research, Tohoku University, Sendai 980-8577 (Japan); Lķotin, Jean [Laboratoire National des Champs Magnķtiques Intenses, CNRS-UJF-UPS-INSA, Toulouse (France)] [Laboratoire National des Champs Magnķtiques Intenses, CNRS-UJF-UPS-INSA, Toulouse (France); Kono, Junichiro, E-mail: email@example.com [Department of Electrical and Computer Engineering, Rice University, Houston, Texas 77005 (United States) [Department of Electrical and Computer Engineering, Rice University, Houston, Texas 77005 (United States); Department of Physics and Astronomy, Rice University, Houston, Texas 77005, USA and Department of Materials Science and NanoEngineering, Rice University, Houston, Texas 77005 (United States)
We have developed a mini-coil pulsed magnet system with direct optical access, ideally suited for nonlinear and ultrafast spectroscopy studies of materials in high magnetic fields up to 30 T. The apparatus consists of a small coil in a liquid nitrogen cryostat coupled with a helium flow cryostat to provide sample temperatures down to below 10 K. Direct optical access to the sample is achieved with the use of easily interchangeable windows separated by a short distance of ?135 mm on either side of the coupled cryostats with numerical apertures of 0.20 and 0.03 for measurements employing the Faraday geometry. As a demonstration, we performed time-resolved and time-integrated photoluminescence measurements as well as transmission measurements on InGaAs quantum wells.
Optical pumping and spectroscopy of Cs vapor at high magnetic field
Olsen, B. A.; Patton, B.; Jau, Y.-Y.; Happer, W. [Joseph Henry Laboratory, Department of Physics, Princeton University, Princeton, New Jersey 08544 (United States)
We have measured changes in the ground-state populations of Cs vapor induced by optical pumping at high magnetic field. The 2.7-T field of our experiments is strong enough to decouple the nuclear and electronic spins, allowing us to independently measure each population. The spatial dependence of the Cs populations in small amounts of buffer gas obeys a simple coupled diffusion model and the relative populations reveal the details of relaxation within the vapor cell. Optical pumping can produce high nuclear polarization in the Cs vapor due to perturbations of the hyperfine interaction during collisions with buffer-gas particles and depending on the pumping transition, radiation trapping can strongly influence the electronic and nuclear polarizations in the vapor.
Feasibility study of Nb3Al Rutherford cable for high field accelerator magnet application
Yamada, R.; /Fermilab; Kikuchi, A.; /Tsukuba Magnet Lab.; Ambrosio, G.; Andreev, N.; Barzi, E.; Cooper, C.; Feher, S.; Kashikhin, V.V.; Lamm, M.; Novitski, I.; /Fermilab; Takeuchi, T.; /Tsukuba Magnet Lab.; Tartaglia, M.; Turrioni, D.; /Fermilab; Verweij, A.P.; /CERN; Wake, M.; Willering, G; /Tsukuba Magnet Lab.; Zlobin, A.V.; /Fermilab
Feasibility study of Cu stabilized Nb{sub 3}Al strand and Rutherford cable for the application to high field accelerator magnets are being done at Fermilab in collaboration with NIMS. The Nb{sub 3}Al strand, which was developed and manufactured at NIMS in Japan, has a non-copper Jc of about 844 A/mm{sup 2} at 15 Tesla at 4.2 K, a copper content of 50%, and filament size of about 50 microns. Rutherford cables with 27 Nb{sub 3}Al strands of 1.03 mm diameter were fabricated and tested. Quench tests on a short cable were done to study its stability with only its self field, utilizing a high current transformer. A pair of 2 meter long Nb{sub 3}Al cables was tested extensively at CERN at 4.3 and 1.9 K up to 11 Tesla including its self field with a high transport current of 20.2 kA. In the low field test we observed instability near splices and in the central region. This is related to the flux-jump like behavior, because of excessive amount of Nb in the Nb{sub 3}Al strand. There is possibility that the Nb in Nb{sub 3}Al can cause instability below 2 Tesla field regions. We need further investigation on this problem. Above 8 Tesla, we observed quenches near the critical surface at fast ramp rate from 1000 to 3000 A/sec, with quench velocity over 100 m/sec. A small racetrack magnet was made using a 14 m of Rutherford cable and successfully tested up to 21.8 kA, corresponding to 8.7 T.
Low virial parameters in molecular clouds: Implications for high-mass star formation and magnetic fields
Kauffmann, Jens; Pillai, Thushara [Astronomy Department, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125 (United States); Goldsmith, Paul F., E-mail: email@example.com, E-mail: firstname.lastname@example.com [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Boulevard, Pasadena, CA 91109 (United States)
Whether or not molecular clouds and embedded cloud fragments are stable against collapse is of utmost importance for the study of the star formation process. Only 'supercritical' cloud fragments are able to collapse and form stars. The virial parameter ? = M {sub vir}/M, which compares the virial mass to the actual mass, provides one way to gauge stability against collapse. Supercritical cloud fragments are characterized by ? ? 2, as indicated by a comprehensive stability analysis considering perturbations in pressure and density gradients. Past research has suggested that virial parameters ? ? 2 prevail in clouds. This would suggest that collapse toward star formation is a gradual and relatively slow process and that magnetic fields are not needed to explain the observed cloud structure. Here, we review a range of very recent observational studies that derive virial parameters <<2 and compile a catalog of 1325 virial parameter estimates. Low values of ? are in particular observed for regions of high-mass star formation (HMSF). These observations may argue for a more rapid and violent evolution during collapse. This would enable 'competitive accretion' in HMSF, constrain some models of 'monolithic collapse', and might explain the absence of high-mass starless cores. Alternatively, the data could point at the presence of significant magnetic fields ?1 mG at high gas densities. We examine to what extent the derived observational properties might be biased by observational or theoretical uncertainties. For a wide range of reasonable parameters, our conclusions appear to be robust with respect to such biases.
Stress Analysis of a High Temperature Superconductor Coil Wound With Bi-2223/Ag Tapes for High Field HTS/LTS NMR Magnet Application
Kiyoshi, Tsukasa
The electromagnetic stress distribution inside a HTS insert is one of the key issues for construction of a high field high/low temperature superconductor (HTS/LTS) magnet. The rmiddotJmiddotB formulae is widely used for ...
Solar coronal magnetic field topology inferred from high resolution optical and x-ray movies
Tarbell, T.; Frank, Z.; Hurlburt, N.; Morrison, M.; Shine, R.; Title, A.; Acton, L.
The authors are using high resolution digital movies of solar active regions in optical and X-ray wavelengths to study solar flares and other transients. The optical movies were collected at the Swedish Solar Observatory on La Palma using the Lockheed tunable filtergraph system, in May-July, 1992. They include longitudinal and transverse magnetograms, H-alpha Doppler and intensity images at many wavelengths, Ca K, Na D, and white light images. Simultaneous X-ray images from Yohkoh are available much of the time. Several ways to establish the connectivity of some coronal magnetic field lines are being explored. Some of the clues available are: magnetic footpoint polarities and transverse field direction; H-alpha fibrils and loops seen in several wavelengths; proper motion and Dopper shifts of blobs moving along field lines; footprint brightening in micro-flares; spreading of flare ribbons during gradual phases of flares; X-ray morphology and correlations with H-alpha; and draining of flare loops. Examples of each of these will be shown on video.
Mode conversion and absorption of fast waves at high ion cyclotron harmonics in inhomogeneous magnetic fields
Cho, Suwon, E-mail: firstname.lastname@example.com [Department of Physics, Kyonggi University, Suwon, Kyonggi-Do 443-760 (Korea, Republic of)] [Department of Physics, Kyonggi University, Suwon, Kyonggi-Do 443-760 (Korea, Republic of); Kwak, Jong-Gu [National Fusion Research Institute, Daejeon 305-806 (Korea, Republic of)] [National Fusion Research Institute, Daejeon 305-806 (Korea, Republic of)
The propagation and absorption of high harmonic fast waves is of interest for non-inductive current drives in fusion experiments. The fast wave can be coupled with the ion Bernstein wave that propagates in the high magnetic field side of an ion cyclotron harmonic resonance layer. This coupling and the absorption are analyzed using the hot plasma dispersion relation and a wave equation that was converted from an approximate dispersion relation for the case where ?{sub i}=k{sub ?}{sup 2}?{sub i}{sup 2}/2?1 (where k{sub ?} is the perpendicular wave number and ?{sub i} is the ion Larmor radius). It is found that both reflection and conversion may occur near the harmonic resonance layer but that they decrease rapidly, giving rise to a sharp increase in the absorption as the parallel wave number increases.
Magnetic-field control of near-field radiative heat transfer and the realization of highly tunable hyperbolic thermal emitters
Moncada-Villa, Edwin; Garcia-Vidal, Francisco J; Garcia-Martin, Antonio; Cuevas, Juan Carlos
We present a comprehensive theoretical study of the magnetic field dependence of the near-field radiative heat transfer (NFRHT) between two parallel plates. We show that when the plates are made of doped semiconductors, the near-field thermal radiation can be severely affected by the application of a static magnetic field. We find that irrespective of its direction, the presence of a magnetic field reduces the radiative heat conductance, and dramatic reductions up to 700% can be found with fields of about 6 T at room temperature. We show that this striking behavior is due to the fact that the magnetic field radically changes the nature of the NFRHT. The field not only affects the electromagnetic surface waves (both plasmons and phonon polaritons) that normally dominate the near-field radiation in doped semiconductors, but it also induces hyperbolic modes that progressively dominate the heat transfer as the field increases. In particular, we show that when the field is perpendicular to the plates, the semicond...
Terahertz Spectroscopy of Spin Waves in Multiferroic BiFeO3 in High Magnetic Fields
DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)
Nagel, U.; Fishman, Randy S.; Katuwal, T.; Engelkamp, H.; Talbayev, D.; Yi, Hee Taek; Cheong, S.-W.; R§§m, T.
We have studied the magnetic field dependence of far-infrared active magnetic modes in a single ferroelectric domain BiFeO3 crystal at low temperature. The modes soften close to the critical field of 18.8 T along the [001] (pseudocubic) axis, where the cycloidal structure changes to the homogeneous canted antiferromagnetic state and a new strong mode with linear field dependence appears that persists at least up to 31 T. A microscopic model that includes two Dzyaloshinskii-Moriya interactions and easy-axis anisotropy describes closely both the zero-field spectroscopic modes as well as their splitting and evolution in a magnetic field. The good agreement of theory with experiment suggests that the proposed model provides the foundation for future technological applications of this multiferroic material.
Reduction of the field spectrum linewidth of a multiple quantum well laser in a high magnetic field: spectral properties of quantum dot lasers
Vahala, K.; Arakawa, Y.; Yariv, A.
The field spectrum linewidth of a multiple quantum well laser immersed in a high magnetic field is measured at room temperature and at 165 K. The low-temperature measurements show a decrease of linewidth with increasing magnetic field. We believe this behavior results from the formation of a totally discrete electronic state space. Measurements of the low-temperature luminescence spectrum show that the emission is split into two peaks by the high field with the higher energy peak responsible for lasing action.
Design and commissioning of a high magnetic field muon spin relaxation spectrometer at the ISIS pulsed neutron and muon source
Lord, J. S.; McKenzie, I.; Baker, P. J.; Cottrell, S. P.; Giblin, S. R.; Hillier, A. D.; Holsman, B. H.; King, P. J. C.; Nightingale, J. B.; Pratt, F. L.; Rhodes, N. J. [ISIS Facility, STFC Rutherford Appleton Laboratory, Chilton, Oxon OX11 0QX (United Kingdom); Blundell, S. J.; Lancaster, T. [Clarendon Laboratory, Department of Physics, Oxford University, Parks Road, Oxford OX1 3PU (United Kingdom); Good, J.; Mitchell, R.; Owczarkowski, M.; Poli, S. [Cryogenic Limited, 30 Acton Park Industrial Estate, The Vale, Acton, London W3 7QE (United Kingdom); Scheuermann, R. [Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institut, CH-5232 Villigen PSI (Switzerland); Salman, Z. [ISIS Facility, STFC Rutherford Appleton Laboratory, Chilton, Oxon OX11 0QX (United Kingdom); Clarendon Laboratory, Department of Physics, Oxford University, Parks Road, Oxford OX1 3PU (United Kingdom)
The high magnetic field (HiFi) muon instrument at the ISIS pulsed neutron and muon source is a state-of-the-art spectrometer designed to provide applied magnetic fields up to 5 T for muon studies of condensed matter and molecular systems. The spectrometer is optimised for time-differential muon spin relaxation studies at a pulsed muon source. We describe the challenges involved in its design and construction, detailing, in particular, the magnet and detector performance. Commissioning experiments have been conducted and the results are presented to demonstrate the scientific capabilities of the new instrument.
Characterization of a high-temperature superconducting conductor on round core cables in magnetic fields up to 20 T
van der Laan, Danko [Advanced Conductor Technologies; Noyes, Patrick [National High Magnetic Field Laboratory; Miller, George [National High Magnetic Field Laboratory; Weijers, Hubertus [National High Magnetic Field Laboratory; Willering, Gerard [CERN
The next generation of high-'¼üeld magnets that will operate at magnetic '¼üelds substantially above 20 T, or at temperatures substantially above 4.2 K, requires high-temperature superconductors (HTS). Conductor on round core (CORC) cables, in which RE-Ba{sub 2}Cu{sub 3}O{sub 7-{delta}} (RE = rare earth) (REBCO) coated conductors are wound in a helical fashion on a fl?exible core, are a practical and versatile HTS cable option for low-inductance, high-fiüeld magnets. We performed the fiürst tests of CORC magnet cables in liquid helium in magnetic fiüelds of up to 20 T. A record critical current I{sub c} of 5021 A was measured at 4.2 K and 19 T. In a cable with an outer diameter of 7.5 mm, this value corresponds to an engineering current density J{sub e} of 114 A mm{sup -2} , the highest J{sub e} ever reported for a superconducting cable at such high magnetic fields. Additionally, the fiürst magnet wound from an HTS cable was constructed from a 6 m-long CORC cable. The 12-turn, double-layer magnet had an inner diameter of 9 cm and was tested in a magnetic fiüeld of 20 T, at which it had an I{sub c} of 1966 A. The cables were quenched repetitively without degradation during the measurements, demonstrating the feasibility of HTS CORC cables for use in high-fiüeld magnet applications.
Electric power high-voltage transmission lines: Design options, cost, and electric and magnetic field levels
Stoffel, J.B.; Pentecost, E.D.; Roman, R.D.; Traczyk, P.A.
This report provides background information about (1) the electric and magnetic fields (EMFs) of high-voltage transmission lines at typical voltages and line configurations and (2) typical transmission line costs to assist on alternatives in environmental documents. EMF strengths at 0 {+-} 200 ft from centerline were calculated for ac overhead lines, and for 345 and 230-kV ac underground line and for a {+-}450-kV dc overhead line. Compacting and height sensitivity factors were computed for the variation in EMFs when line conductors are moved closer or raised. Estimated costs for the lines are presented and discussed so that the impact of using alternative strategies for reducing EMF strengths and the implications of implementing the strategies can be better appreciated.
A High Field Magnet Design for A Future Hadron Collider==== R. Gupta, K. Chow, D. Dietderich, S. Gourlay, G. Millos, A. McInturff, R. Scanlan
Gupta, Ramesh
A High Field Magnet Design for A Future Hadron Collider==== R. Gupta, K. Chow, D. Dietderich, S the completion of LHC. This paper presents a high field magnet design option based on Nb3Sn technology. A preliminary magnetic and mechanical design of a 14-16 T, 2-in-1 dipole based on the "common coil design
High-Temperature Superconducting Cable Testing Gregory S. Boebinger, National High Magnetic Field Laboratory
Weston, Ken
and need for improvement. A 20-strand cable sample was wound into a 12-turn coil, which is also a first of HTS coil technology needed, for example, for the design of a 60 T DC hybrid magnet at the MagLab PhD student who recently formed a company to develop his ideas for making cables out of REBCO coated
Hybrid magnet devices for molecule manipulation and small scale high gradient-field applications
Humphries, David E. (El Cerrito, CA); Hong, Seok-Cheol (Seoul, KR); Cozzarelli, legal representative, Linda A. (Berkeley, CA); Pollard, Martin J. (El Cerrito, CA); Cozzarelli, Nicholas R. (Berkeley, CA)
The present disclosure provides a high performance hybrid magnetic structure made from a combination of permanent magnets and ferromagnetic pole materials which are assembled in a predetermined array. The hybrid magnetic structure provides means for separation and other biotechnology applications involving holding, manipulation, or separation of magnetizable molecular structures and targets. Also disclosed are hybrid magnetic tweezers able to exert approximately 1 nN of force to 4.5 .mu.m magnetic bead. The maximum force was experimentally measured to be .about.900 pN which is in good agreement with theoretical estimations and other measurements. In addition, a new analysis scheme that permits fast real-time position measurement in typical geometry of magnetic tweezers has been developed and described in detail.
Design of HQ -- a High Field Large Bore Nb3Sn Quadrupole Magnet for LARP
Felice, H.; Ambrosio, G.; Anerella, M.; Bossert, R.; Caspi, S.; Cheng, D.; Dietderich, D.; Ferracin, P.; Ghosh, A. K.; Hafalia, R.; Hannaford, C. R.; Kashikhin, V.; Schmalze, J.; Prestemon, S.; Sabbi, G. L.; Wanderer, P.; Zlobin, A. V.
In support of the Large Hadron Collider luminosity upgrade, a large bore (120 mm) Nb{sub 3}Sn quadrupole with 15 T peak coil field is being developed within the framework of the US LHC Accelerator Research Program (LARP). The 2-layer design with a 15 mm wide cable is aimed at pre-stress control, alignment and field quality while exploring the magnet performance limits in terms of gradient, forces and stresses. In addition, HQ will determine the magnetic, mechanical, and thermal margins of Nb{sub 3}Sn technology with respect to the requirements of the luminosity upgrade at the LHC.
Development of a magnetohydrodynamic code for axisymmetric, high-. beta. plasmas with complex magnetic fields
Cook, G.O. Jr.
The Topolotron is an axisymmetric, toroidal magnetic fusion concept in which two-dimensional effects are important, as well as all three magnetic field components. The particular MHD model employed is basically the one-fluid, two-temperature model using classical Braginskii transport with viscous effects ignored. The model is augmented by Saha-Boltzmann dissociation and partial ionization physics, a simple radiation loss mechanism, and an additional resistivity due to electron-neutral collisions. While retaining all velocity and magnetic field components, the assumption of axisymmetry is made, and the resulting equations are expanded in cylindrical coordinates. The major approximation technique is then applied: spline collocation, which reduces these equations to a set of ordinary differential equations.
Recent Test Results of the High Field Nb3Sn Dipole Magnet HD2
Ferracin, P.; Bingham, B.; Caspi, S.; Cheng, D. W.; Dietderich, D. R.; Felice, H.; Hafalia, A. R.; Hannaford, C. R.; Joseph, J.; Lietzke, A. F.; Lizarazo, J.; Sabbi, G.; Wang, X.
The 1 m long Nb{sub 3}Sn dipole magnet HD2, fabricated and tested at Lawrence Berkeley National Laboratory, represents a step towards the development of block-type accelerator quality magnets operating in the range of 13-15 T. The magnet design features two coil modules composed of two layers wound around a titanium-alloy pole. The layer 1 pole includes a round cutout to provide room for a bore tube with a clear aperture of 36 mm. After a first series of tests where HD2 reached a maximum bore field of 13.8 T, corresponding to an estimated peak field on the conductor of 14.5 T, the magnet was disassembled and reloaded without the bore tube and with a clear aperture increased to 43 mm. We describe in this paper the magnet training observed in two consecutive tests after the removal of the bore tube, with a comparison of the quench performance with respect to the previous tests. An analysis of the voltage signals recorded before and after training quenches is then presented and discussed, and the results of coil visual inspections reported.
Use of High Magnetic Fields to Improve Material Properties for Hydraulics, Automotive and Truck Components
Ludtka, Gerard Michael [ORNL; Ludtka, Gail Mackiewicz- [ORNL; Wilgen, John B [ORNL; Kisner, Roger A [ORNL; Ahmad, Aquil [Eaton Corporation
In this CRADA, research and development activities were successfully conducted on magnetic processing effects for the purpose of manipulating microstructure and the application specific performance of three alloys provided by Eaton (alloys provided were: carburized steel, plain low carbon steel and medium carbon spring steel). Three specific industrial/commercial application areas were considered where HMFP can be used to provide significant energy savings and improve materials performance include using HMFP to: 1.) Produce higher material strengths enabling higher torque bearing capability for drive shafts and other motor components; 2.) Increase the magnetic response in an iron-based material, thereby improving its magnetic permeability resulting in improved magnetic coupling and power density, and 3.) Improve wear resistance. The very promising results achieved in this endeavor include: 1.) a significant increase in tensile strength and a major reduction in volume percent retained austenite for the carburized alloy, and 2.) a substantial improvement in magnetic perm respect to a no-field processed sample (which also represents a significant improvement over the nominal conventional automotive condition of no heat treatment). The successful completion of these activities has resulted in the current 3-year CRADA No. NFE-09-02522 Prototyping Energy Efficient ThermoMagnetic and Induction Hardening for Heat Treat and Net Shape Forming Applications .
Characterization of High Current RRP(R) Wires as a Function of Magnetic Field, Temperature and Strain
Godeke, A.; Mentink, M.G.T.; Dietderich, D. R.; den Ouden, A.
A new instrument for the characterization of superconducting materials as a function of Magnetic Field, Temperature and Strain, was designed, constructed and tested at Lawrence Berkeley National Laboratory (LBNL). A U-shaped bending spring was selected, since that design has proven to enable accurate characterizations of a multitude of superconducting materials for more than a decade. The new device is validated though measurements on very high current Rod Restack Processed (RRP) Internal-Tin (IT) wires, for which we will present initial results, including parameterizations of the superconducting phase boundaries and comparisons with other wire types. Accurate parametrization of modern high magnetic field conductors is important for the analysis of the performance of magnet systems.
Insert Coil Test for HEP High Field Magnets Using YBCO Coated Conductor Tapes
Lombardo, V.; Barzi, E.; Turrioni, D.; Zlobin, A.V.; /Fermilab
The final beam cooling stages of a Muon Collider may require DC solenoid magnets with magnetic fields of 30-50 T. In this paper we present progress in insert coil development using commercially available YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} Coated Conductor. Technological aspects covered in the development, including coil geometry, insulation, manufacturing process and testing are summarized and discussed. Test results of double pancake coils operated in liquid nitrogen and liquid helium are presented and compared with the performance of YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} tape short samples.
Magnetic Field Measurement System
Kulesza, Joe; Johnson, Eric; Lyndaker, Aaron; Deyhim, Alex; Waterman, Dave; Blomqvist, K. Ingvar [Advanced Design Consulting USA, 126 Ridge Road, P.O. Box 187, Lansing, NY 14882 (United States); Dunn, Jonathan Hunter [MAX-lab, SE-221 00 Lund (Sweden)
A magnetic field measurement system was designed, built and installed at MAX Lab, Sweden for the purpose of characterizing the magnetic field produced by Insertion Devices (see Figure 1). The measurement system consists of a large granite beam roughly 2 feet square and 14 feet long that has been polished beyond laboratory grade for flatness and straightness. The granite precision coupled with the design of the carriage yielded minimum position deviations as measured at the probe tip. The Hall probe data collection and compensation technique allows exceptional resolution and range while taking data on the fly to programmable sample spacing. Additional flip coil provides field integral data.
Effect of Field Dependent Core Size on Reversible Magnetization of High-? Superconductors
Kogan, V. G. [Ames Laboratory and Iowa State University; Prozorov, R. [Ames Laboratory and Iowa State University; Bud'ko, S. L. [Ames Laboratory; Canfield, P. C. [Ames Laboratory; Thompson, James R [ORNL; Karpinski, J. [Swiss Federal Institute of Technology; Zhigadlo, N. D. [Swiss Federal Institute of Technology; Miranovic, P. [University of Montenegro, Serbia and Montenegro
The field dependence of the vortex core size {zeta}(B) is incorporated in the London model, in order to describe reversible magnetization M(B,T) for a number of materials with large Ginzburg-Landau parameter {kappa}. The dependence {zeta}(B) is directly related to deviations in M(ln B) from linear behavior prescribed by the standard London model. A simple method to extract {zeta}(B) from the magnetization data is proposed. For most materials examined, {zeta}(B) so obtained decreases with increasing field and is in qualitative agreement both with behavior extracted from {micro}SR and small-angle neutron-scattering data and with that predicted theoretically.
Discovery of magnetic fields in CPNs
S. Jordan; K. Werner; S. J. O'Toole
For the first time we have directly detected magnetic fields in central stars of planetary nebulae by means of spectro-polarimetry with FORS1 at the VLT. In all four objects of our sample we found kilogauss magnetic fields, in NGC 1360 and LSS1362 with very high significance, while in Abell36 and EGB5 the existence of a magnetic field is probable but with less certainty. This discovery supports the hypothesis that the non-spherical symmetry of most planetary nebulae is caused by magnetic fields in AGB stars. Our high discovery rate demands mechanisms to prevent full conservation of magnetic flux during the transition to white dwarfs.
Heat treatment and Magnetic Field Procedure A 32mm diameter bore resistive magnet with a 33T maximum field strength at the National High
Cambridge, University of
-heating coil set-up has been designed to heat and cool the specimen while inside the bore of the magnetC/s to the annealing temperature. A 3-minute hold at 1000║C was performed to fully transform the initial microstructure for the field to reach 30T. Specimen cooling was controlled via feedback loop such that by decreasing power
Assembly and Test of HD2, a 36 mm bore high field Nb3Sn Dipole Magnet
Ferracin, P.; Bingham, B.; Caspi, S.; Cheng, D. W,.; Dietderich, D. R.; Felice, H.; Godeke, A.; Hafalia, A. R.; Hannaford, C. R.; Joseph, J.; Lietzke, A. F.; Lizarazo, J.; Sabbi, G.; Trillaud, F.; Wang, X.
We report on the fabrication, assembly, and test of the Nb{sub 3}Sn dipole magnet HD2. The magnet, aimed at demonstrating the application of Nb{sub 3}Sn superconductor in high field accelerator-type dipoles, features a 36 mm clear bore surrounded by block-type coils with tilted ends. The coil design is optimized to minimize geometric harmonics in the aperture and the magnetic peak field on the conductor in the coil ends. The target bore field of 15 T at 4.3 K is consistent with critical current measurements of extracted strands. The coils are horizontally pre-stressed during assembly using an external aluminum shell pre-tensioned with water-pressurized bladders. Axial pre-loading of the coil ends is accomplished through two end plates and four aluminum tension rods. The strain in coil, shell, and rods is monitored with strain gauges during assembly, cool-down and magnet excitation, and compared with 3D finite element computations. Magnet's training performance, quench locations, and ramp-rate dependence are then analyzed and discussed.
Evidence of Magnetic Breakdown on the Defects With Thermally Suppressed Critical Field in High Gradient SRF Cavities
Eremeev, Grigory [JLAB; Palczewski, Ari [JLAB
At SRF 2011 we presented the study of quenches in high gradient SRF cavities with dual mode excitation technique. The data differed from measurements done in 80's that indicated thermal breakdown nature of quenches in SRF cavities. In this contribution we present analysis of the data that indicates that our recent data for high gradient quenches is consistent with the magnetic breakdown on the defects with thermally suppressed critical field. From the parametric fits derived within the model we estimate the critical breakdown fields.
Electron-Irradiation Induced Nanocrystallization of Pb(II) in Silica Gels Prepared in High Magnetic Field
Kaito, Takamasa; Kaito, Chihiro
In a previous study, structure of silica gels prepared in a high magnetic field was investigated. While a direct application of such anisotropic silica gels is for an optical anisotropic medium possessing chemical resistance, we show here their possibility of medium in materials processing. In this direction, for example, silica hydrogels have so far been used as media of crystal growth. In this paper, as opposed to the soft-wet state, dried silica gels have been investigated. We have found that lead (II) nanocrystallites were formed induced by electron irradiation to lead (II)-doped dried silica gels prepared in a high magnetic field such as B = 10 T. Hydrogels made from a sodium metasilicate solution doped with lead (II) acetate were prepared. The dried specimens were irradiated by electrons in a transmission electron microscope environment. Electron diffraction patterns indicated the crystallinity of lead (II) nanocrystallites depending on B. An advantage of this processing technique is that the crystallin...
Method for improving performance of high temperature superconductors within a magnetic field
Wang, Haiyan (Los Alamos, NM); Foltyn, Stephen R. (Los Alamos, NM); Maiorov, Boris A. (Los Alamos, NM); Civale, Leonardo (Los Alamos, NM)
The present invention provides articles including a base substrate including a layer of an oriented cubic oxide material having a rock-salt-like structure layer thereon; and, a buffer layer upon the oriented cubic oxide material having a rock-salt-like structure layer, the buffer layer having an outwardly facing surface with a surface morphology including particulate outgrowths of from 10 nm to 500 run in size at the surface, such particulate outgrowths serving as flux pinning centers whereby the article maintains higher performance within magnetic fields than similar articles without the necessary density of such outgrowths.
The LLNL HFTF (High-Field Test Facility): A flexible superconducting test facility for fusion magnet development
Miller, J.R.; Chaplin, M.R.; Leber, R.L.; Rosdahl, A.R.
The High-Field Test Facility (HFTF) is a flexible and, in many ways, unique facility at Lawrence Livermore National Laboratory (LLNL) for providing the test capabilities needed to develop the superconducting magnet systems of the next generation fusion machines. The superconducting coil set in HFTF has been operated successfully at LLNL, but in its original configuration, its utility as a test facility was somewhat restricted and cryogenic losses were intolerable. A new cryostat for the coil set allows the magnet system to remain cold indefinitely so the system is available on short notice to provide high fields (about 11 T) inside a reasonably large test volume (0.3-m diam). The test volume is physically and thermally isolated from the coil volume, allowing test articles to be inserted and removed without disturbing the coil cryogenic volume, which is maintained by an on-line refrigerator. Indeed, with the proper precautions, it is even unnecessary to drop the field in the HFTF during such an operation. The separate test volume also allows reduced temperature operation without the expense and complication of subcooling the entire coil set (about 20-t cold mass). The HFTF has thus become a key facility in the LLNL magnet development program, where the primary goal is to demonstrate the technology for producing fields to 15 T with winding-pack current densities of 40 A.mm/sup -2/ in coils sized for fusion applications. 4 refs., 4 figs., 1 tab.
Transient magnetic field and temperature modeling in large magnet applications
Gurol, H.; Hardy, G.E.; Peck, S.D.; Leung, E. (General Dynamics Corp., San Diego, CA (USA). Space Systems Div.)
This paper discusses a coupled magnetic/thermal model developed to study heat and magnetic field diffusion in conducting materials subject to time-varying external fields. There are numerous applications, both military and commercial. These include: energy storage devices, pulsed power transformers, and electromagnetic launchers. The time scales of interest may range from a magnetic field pulse of a microsecond in an electromagnetic launcher, to hundreds of seconds in an energy storage magnet. The problem can be dominated by either the magnetic field or heat diffusion, depending on the temperature and the material properties of the conductor. In general, heat diffuses much more rapidly in high electrical conductivity materials of cryogenic temperatures. The magnetic field takes longer to diffuse, since screening currents can be rapidly set up which shield the interior of the material from further magnetic field penetration. Conversely, in high resistivity materials, the magnetic field diffuses much more rapidly. A coupled two-dimensional thermal/magnetic model has been developed. The results of this model, showing the time and spatial variation of the magnetic field and temperature, are discussed for the projectile of an electromagnetic launcher.
On the GCR intensity and the inversion of the heliospheric magnetic field during the periods of the high solar activity
Krainev, M B
We consider the long-term behavior of the solar and heliospheric parameters and the GCR intensity in the periods of high solar activity and the inversions of heliospheric magnetic field (HMF). The classification of the HMF polarity structures and the meaning of the HMF inversion are discussed. The procedure is considered how to use the known HMF polarity distribution for the GCR intensity modeling during the periods of high solar activity. We also briefly discuss the development and the nearest future of the sunspot activity and the GCR intensity in the current unusual solar cycle 24.
Formation of Collisionless High-{beta} Plasmas by Odd-Parity Rotating Magnetic Fields
Cohen, S. A.; Berlinger, B.; Brunkhorst, C.; Brooks, A.; Ferraro, N.; Lundberg, D. P.; Roach, A. [Princeton Plasma Physics Laboratory, Princeton University, Princeton, New Jersey (United States); Glasser, A. H. [Los Alamos National Laboratory, Los Alamos, New Mexico (United States)
Odd-parity rotating magnetic fields (RMF{sub o}) applied to mirror-configuration plasmas have produced average electron energies exceeding 200 eV at line-averaged electron densities of {approx}10{sup 12} cm{sup -3}. These plasmas, sustained for over 10{sup 3}{tau}{sub Alfven}, have low Coulomb collisionality, v{sub c}*{identical_to}L/{lambda}{sub C}{approx}10{sup -3}, where {lambda}{sub C} is the Coulomb scattering mean free path and L is the plasma's characteristic half length. Divertors allow reduction of the electron-neutral collision frequency to values where the RMF{sub o} coupling indicates full penetration of the RMF{sub o} to the major axis.
Low field magnetic resonance imaging
Pines, Alexander (Berkeley, CA); Sakellariou, Dimitrios (Billancourt, FR); Meriles, Carlos A. (Fort Lee, NJ); Trabesinger, Andreas H. (London, GB)
A method and system of magnetic resonance imaging does not need a large homogenous field to truncate a gradient field. Spatial information is encoded into the spin magnetization by allowing the magnetization to evolve in a non-truncated gradient field and inducing a set of 180 degree rotations prior to signal acquisition.
A new probe of magnetic fields during high-mass star formation: Zeeman splitting of 6.7 GHz methanol masers
W. H. T. Vlemmings
Context: The role of magnetic fields during high-mass star formation is a matter of fierce debate, yet only a few direct probes of magnetic field strengths are available. Aims: The magnetic field is detected in a number of massive star-forming regions through polarization observations of 6.7 GHz methanol masers. Although these masers are the most abundant of the maser species occurring during high-mass star formation, most magnetic field measurements in the high-density gas currently come from OH and H2 O maser observations. Methods: The 100-m Effelsberg telescope was used to measure the Zeeman splitting of 6.7 GHz methanol masers for the first time. The observations were performed on a sample of 24 bright northern maser sources. Results: Significant Zeeman splitting is detected in 17 of the sources with an average magnitude of 0.56 m/s . Using the current best estimate of the 6.7 GHz methanol maser Zeeman splitting coefficient and a geometrical correction, this corresponds to an absolute magnetic field strength of 23 mG in the methanol maser region. Conclusions: The magnetic field is dynamically important in the dense maser regions. No clear relation is found with the available OH maser magnetic field measurements. The general sense of direction of the magnetic field is consistent with other Galactic magnetic field measurements, although a few of the masers display a change of direction between different maser features. Due to the abundance of methanol masers, measuring their Zeeman splitting provides the opportunity to construct a comprehensive sample of magnetic fields in high-mass star-forming regions.
The spontaneous generation of magnetic fields at high temperature in SU(2)-gluodynamics on a lattice
Vadim Demchik; Vladimir Skalozub
The spontaneous generation of the chromomagnetic field at high temperature is investigated in a lattice formulation of the SU(2)-gluodynamics. The procedure of studying this phenomenon is developed. The Monte Carlo simulations of the free energy on the lattices 2 \\times 8^3, 2\\times 16^3 and 4 \\times 8^3 at various temperatures are carried out. The creation of the field is indicated by means of the \\chi^2-analysis of the data set accumulating 5-10 millions MC configurations. A comparison with the results of other approaches is done.
Reduction of the spectral linewidth of semiconductor lasers with quantum wire effects: Spectral properties of GaAlAs double heterostructure lasers in high magnetic fields
Arakawa, Y.; Vahala, K.; Yariv, A.; Lau, K.
The spectral linewidth of a GaAlAs double heterostructure laser placed in a high magnetic field is measured at 190 K. It is found that the power-dependent spectral linewidth is reduced by a factor of 0.6 in a magnetic field of 19 T. This reduction is believed to result mainly from the reduction of the linewidth enhancement factor ..alpha.. due to a quasi-one-dimensional electronic system formed by the high magnetic field (i.e., by quantum wire effects).
Enhanced modulation bandwidth of GaAlAs double heterostructure lasers in high magnetic fields: Dynamic response with quantum wire effects
Arakawa, Y.; Vahala, K.; Yariv, A.; Lau, K.
The modulation bandwidth of GaAlAs double heterostructure (DH) lasers in high magnetic fields is measured. We found that the modulation bandwidth is enhanced by 1.4 x with a magnetic field of 20 T. This improvement is believed to result from the increase of the differential gain due to two-dimensional carrier confinement effects in the high magnetic field (quantum wire effects). A comparison of the experimental results with a theoretical analysis indicates that the intraband relaxation time tau/sub in/ of the measured DH laser in the range of 0.1 to 0.2 ps.
Chaotic electron dynamics around a single elliptically shaped antidot High Magnetic Field Laboratory CNRS, Boite Postale 166, F-38042 Grenoble, France
Gusev, Guennady
, Boite Postale 166, F-38042 Grenoble, France J. C. Portal High Magnetic Field Laboratory CNRS, Boite, Russia Received 30 April 1996 The classical dynamics of a charged particle colliding ballistically around
Exploration of Quench Initiation Due to Intentional Geometrical Defects in a High Magnetic Field Region of an SRF Cavity
J. Dai, K. Zhao, G.V. Eremeev, R.L. Geng, A.D. Palczewski; Dai, J. [Thomas Jefferson National Accelerator Facility, Newport News, VA (United States); Palczewski, A. D. [Thomas Jefferson National Accelerator Facility, Newport News, VA (United States); Eremeev, G. V. [Thomas Jefferson National Accelerator Facility, Newport News, VA (United States); Geng, R. L. [Thomas Jefferson National Accelerator Facility, Newport News, VA (United States); Zhao, K. [Institute of Heavy Ion Physics, Peking University, Beijing (China)
A computer program which was used to simulate and analyze the thermal behaviors of SRF cavities has been developed at Jefferson Lab using C++ code. This code was also used to verify the quench initiation due to geometrical defects in high magnetic field region of SRF cavities. We built a CEBAF single cell cavity with 4 artificial defects near equator, and this cavity has been tested with T-mapping. The preheating behavior and quench initiation analysis of this cavity will be presented here using the computer program.
Tiwari, Sanjiv Kumar; Venkatakrishnan, P. [Udaipur Solar Observatory, Physical Research Laboratory, Dewali, Bari Road, Udaipur-313 001 (India); Sankarasubramanian, K. [Space Astronomy and Instrumentation Division, ISRO Satellite Center, Airport Road, Vimanapura, Bangalore-560017 (India)], E-mail: email@example.com, E-mail: email@example.com, E-mail: email@example.com
The presence of fine structures in sunspot vector magnetic fields has been confirmed from Hinode as well as other earlier observations. We studied 43 sunspots based on the data sets taken from ASP/DLSP, Hinode (SOT/SP), and SVM (USO). In this Letter, (1) we introduce the concept of signed shear angle (SSA) for sunspots and establish its importance for non-force-free fields. (2) We find that the sign of global {alpha} (force-free parameter) is well correlated with that of the global SSA and the photospheric chirality of sunspots. (3) Local {alpha} patches of opposite signs are present in the umbra of each sunspot. The amplitude of the spatial variation of local {alpha} in the umbra is typically of the order of the global {alpha} of the sunspot. (4) We find that the local {alpha} is distributed as alternately positive and negative filaments in the penumbra. The amplitude of azimuthal variation of the local {alpha} in the penumbra is approximately an order of magnitude larger than that in the umbra. The contributions of the local positive and negative currents and {alpha} in the penumbra cancel each other giving almost no contribution for their global values for the whole sunspot. (5) Arc-like structures (partial rings) with a sign opposite to that of the dominant sign of {alpha} of the umbral region are seen at the umbral-penumbral boundaries of some sunspots. (6) Most of the sunspots studied belong to the minimum epoch of the 23rd solar cycle and do not follow the so-called hemispheric helicity rule.
Accurate correction of magnetic field instabilities for high-resolution isochronous mass measurements in storage rings
P. Shuai; H. S. Xu; Y. H. Zhang; Yu. A. Litvinov; M. Wang; X. L. Tu; K. Blaum; X. H. Zhou; Y. J. Yuan; G. Audi; X. L. Yan; X. C. Chen; X. Xu; W. Zhang; B. H. Sun; T. Yamaguchi; R. J. Chen; C. Y. Fu; Z. Ge; W. J. Huang; D. W. Liu; Y. M. Xing; Q. Zeng
Isochronous mass spectrometry (IMS) in storage rings is a successful technique for accurate mass measurements of short-lived nuclides with relative precision of about $10^{-5}-10^{-7}$. Instabilities of the magnetic fields in storage rings are one of the major contributions limiting the achievable mass resolving power, which is directly related to the precision of the obtained mass values. A new data analysis method is proposed allowing one to minimise the effect of such instabilities. The masses of the previously measured at the CSRe $^{41}$Ti, $^{43}$V, $^{47}$Mn, $^{49}$Fe, $^{53}$Ni and $^{55}$Cu nuclides were re-determined with this method. An improvement of the mass precision by a factor of $\\sim 1.7$ has been achieved for $^{41}$Ti and $^{43}$V. The method can be applied to any isochronous mass experiment irrespective of the accelerator facility. Furthermore, the method can be used as an on-line tool for checking the isochronous conditions of the storage ring.
Field-dependent critical state of high-Tc superconducting strip simultaneously exposed to transport current and perpendicular magnetic field
Xue, Cun; He, An; Yong, Huadong; Zhou, Youhe, E-mail: email@example.com [Key Laboratory of Mechanics on Disaster and Environment in Western China attached to the Ministry of Education of China, and Department of Mechanics and Engineering Sciences, College of Civil Engineering and Mechanics, Lanzhou University, Lanzhou, Gansu 730000 (China)] [Key Laboratory of Mechanics on Disaster and Environment in Western China attached to the Ministry of Education of China, and Department of Mechanics and Engineering Sciences, College of Civil Engineering and Mechanics, Lanzhou University, Lanzhou, Gansu 730000 (China)
We present an exact analytical approach for arbitrary field-dependent critical state of high-T{sub c} superconducting strip with transport current. The sheet current and flux-density profiles are derived by solving the integral equations, which agree with experiments quite well. For small transport current, the approximate explicit expressions of sheet current, flux-density and penetration depth for the Kim model are derived based on the mean value theorem for integration. We also extend the results to the field-dependent critical state of superconducting strip in the simultaneous presence of applied field and transport current. The sheet current distributions calculated by the Kim model agree with experiments better than that by the Bean model. Moreover, the lines in the I{sub a}-B{sub a} plane for the Kim model are not monotonic, which is quite different from that the Bean model. The results reveal that the maximum transport current in thin superconducting strip will decrease with increasing applied field which vanishes for the Bean model. The results of this paper are useful to calculate ac susceptibility and ac loss.
Fast superconducting magnetic field switch
Goren, Yehuda (Mountain View, CA); Mahale, Narayan K. (The Woodlands, TX)
The superconducting magnetic switch or fast kicker magnet is employed with electron stream or a bunch of electrons to rapidly change the direction of flow of the electron stream or bunch of electrons. The apparatus employs a beam tube which is coated with a film of superconducting material. The tube is cooled to a temperature below the superconducting transition temperature and is subjected to a constant magnetic field which is produced by an external dc magnet. The magnetic field produced by the dc magnet is less than the critical field for the superconducting material, thus, creating a Meissner Effect condition. A controllable fast electromagnet is used to provide a magnetic field which supplements that of the dc magnet so that when the fast magnet is energized the combined magnetic field is now greater that the critical field and the superconducting material returns to its normal state allowing the magnetic field to penetrate the tube. This produces an internal field which effects the direction of motion and of the electron stream or electron bunch. The switch can also operate as a switching mechanism for charged particles.
Table of Contents Page 2National High Magnetic Field Laboratory and Its Forecasted Impact on the Florida Economy
Weston, Ken
Impact on the Florida Economy History and Evaluation of the Economic Impact of the Magnet Lab Forecasted Impact on the Florida Economy The National Science Foundation (NSF) awarded the National High generated by Magnet Lab activities across the broader statewide economy. Since 1990, the Magnet Lab has
Exposure guidelines for magnetic fields
Miller, G.
The powerful magnetic fields produced by a controlled fusion experiment at Lawrence Livermore National Laboratory (LLNL) necessitated the development of personnel-exposure guidelines for steady magnetic fields. A literature search and conversations with active researchers showed that it is currently possible to develop preliminary exposure guidelines for steady magnetic fields. An overview of the results of past research into the bioeffects of magnetic fields was compiled, along with a discussion of hazards that may be encountered by people with sickle-cell anemia or medical electronic and prosthetic implants. The LLNL steady magnetic-field exposure guidelines along with a review of developments concerning the safety of time-varying fields were also presented in this compilation. Guidelines developed elsewhere for time varying fields were also given. Further research is needed to develop exposure standards for both steady or time-varying fields.
Magnetic-field-dosimetry system
Lemon, D.K.; Skorpik, J.R.; Eick, J.L.
A device is provided for measuring the magnetic field dose and peak field exposure. The device includes three Hall-effect sensors all perpendicular to each other, sensing the three dimensional magnetic field and associated electronics for data storage, calculating, retrieving and display.
Multimodal neuroimaging with simultaneous electroencephalogram and high-field functional magnetic resonance imaging
Purdon, Patrick L. (Patrick Lee), 1974-
Simultaneous recording of electroencephalogram (EEG) and functional magnetic resonance imaging (tMRI) is an important emerging tool in functional neuroimaging with the potential to reveal new mechanisms for brain function ...
High field nuclear magnetic resonance in transition metal substituted BaFe{sub 2}As{sub 2}
Garitezi, T. M., E-mail: firstname.lastname@example.com; Lesseux, G. G.; Rosa, P. F. S.; Adriano, C.; Pagliuso, P. G.; Urbano, R. R. [Instituto de FĒsica ōGleb Wataghin,ö UNICAMP, Campinas, SP 13083-859 (Brazil); Reyes, A. P.; Kuhns, P. L. [National High Magnetic Field Laboratory, FSU, Tallahassee, Florida 32306-4005 (United States)
We report high field {sup 75}As nuclear magnetic resonance (NMR) measurements on Co and Cu substituted BaFe{sub 2}As{sub 2} single crystals displaying same structural/magnetic transition T{sub 0}?128??K. From our anisotropy studies in the paramagnetic state, we strikingly found virtually identical quadrupolar splitting and consequently the quadrupole frequency ?{sub Q}?2.57(1)??MHz for both compounds, despite the claim that each Cu delivers 2 extra 3d electrons in BaFe{sub 2}As{sub 2} compared to Co substitution. These results allow us to conclude that a subtle change in the crystallographic structure, particularly in the Fe¢As tetrahedra, must be the most probable tuning parameter to determine T{sub 0} in this class of superconductors rather than electronic doping. Furthermore, our NMR data around T{sub 0} suggest coexistence of tetragonal/paramagnetic and orthorhombic/antiferromagnetic phases between the structural and the spin density wave magnetic phase transitions, similarly to what was reported for K-doped BaFe{sub 2}As{sub 2} [Urbano et al., Phys. Rev. Lett. 105, 107001 (2010)].
Colour superconductivity in a strong magnetic field
Efrain J. Ferrer; Vivian de la Incera; Cristina Manuel
We explore the effects of an applied strong external magnetic field in a three flavour massless colour superconductor. The long-range component of the B field that penetrates the superconductor enhances some quark condensates, leading to a different condensation pattern. The external field also reduces the flavour symmetries in the system, and thus it changes drastically the corresponding low energy physics. Our considerations are relevant for the study of highly magnetized compact stars.
A Study to Develop an Industrial-Scale, Computer-Controlled High Magnetic Field Processing (HMFP) System to Assist in Commercializing the Novel, Enabling HMFP Manufacturing Technology
Ludtka, Gail Mackiewicz- [ORNL; Chourey, Aashish [American Magnetics Inc.
As the original magnet designer and manufacturer of ORNL s 9T, 5-inch ID bore magnet, American Magnetics Inc. (AMI) has collaborated with ORNL s Materials Processing Group s and this partnership has been instrumental in the development of our unique thermo-magnetic facilities and expertise. Consequently, AMI and ORNL have realized that the commercial implementation of the High Magnetic Field Processing (HMFP) technology will require the evolution of robust, automated superconducting (SC) magnet systems that will be cost-effective and easy to operate in an industrial environment. The goal of this project and CRADA is to significantly expedite the timeline for implementing this revolutionary and pervasive cross-cutting technology for future US produced industrial components. The successful completion of this project is anticipated to significantly assist in the timely commercialization and licensing of our HMFP intellectual property for a broad spectrum of industries; and to open up a new market for AMI. One notable outcome of this project is that the ThermoMagnetic Processing Technology WON a prestigious 2009 R&D 100 Awards. This award acknowledges and recognizes our TMP Technology as one of the top 100 innovative US technologies in 2009. By successfully establishing the design requirements for a commercial scale magnetic processing system, this project effort has accomplished a key first step in facilitating the building and demonstration of a superconducting magnetic processing coil, enabling the transition of the High Magnetic Field Processing Technology beyond a laboratory novelty into a commercially viable and industrially scalable Manufacturing Technology.
ARC: A compact, high-field, fusion nuclear science facility and demonstration power plant with demountable magnets
Sorbom, B N; Palmer, T R; Mangiarotti, F J; Sierchio, J M; Bonoli, P; Kasten, C; Sutherland, D A; Barnard, H S; Haakonsen, C B; Goh, J; Sung, C; Whyte, D G
The affordable, robust, compact (ARC) reactor conceptual design study aims to reduce the size, cost, and complexity of a combined fusion nuclear science facility (FNSF) and demonstration fusion Pilot power plant. ARC is a 270 MWe tokamak reactor with a major radius of 3.3 m, a minor radius of 1.1 m, and an on-axis magnetic field of 9.2 T. ARC has rare earth barium copper oxide (REBCO) superconducting toroidal field coils, which have joints to enable disassembly. This allows the vacuum vessel to be replaced quickly, mitigating first wall survivability concerns, and permits a single device to test many vacuum vessel designs and divertor materials. The design point has a plasma fusion gain of Q_p~13.6, yet is fully non-inductive, with a modest bootstrap fraction of only ~63%. Thus ARC offers a high power gain with relatively large external control of the current profile. This highly attractive combination is enabled by the ~23 T peak field on coil with newly available REBCO superconductor technology. External cu...
VOLUME 17 No. 3VOLUME 17 NO. 3 NATIONAL HIGH MAGNETIC FIELD LABORATORY
Weston, Ken
for use as second generation (Gen II) fuels (see page 10). Gen II fuels are biofuels from non-food stuffs-frequency EPR in heterogenous catalysis PAGE 7 Exploring non-food biofuels PAGE 10 #12;VOLUME 17 Ę No. 3 TABLE and theoretical questions Utilizing magnets to explore catalysis The new biofuels? Ion Cyclotron Resonance team
Measurements of magnetic field alignment
Kuchnir, M.; Schmidt, E.E.
The procedure for installing Superconducting Super Collider (SSC) dipoles in their respective cryostats involves aligning the average direction of their field with the vertical to an accuracy of 0.5 mrad. The equipment developed for carrying on these measurements is described and the measurements performed on the first few prototypes SSC magnets are presented. The field angle as a function of position in these 16.6 m long magnets is a characteristic of the individual magnet with possible feedback information to its manufacturing procedure. A comparison of this vertical alignment characteristic with a magnetic field intensity (by NMR) characteristic for one of the prototypes is also presented. 5 refs., 7 figs.
Can Images Obtained With High Field Strength Magnetic Resonance Imaging Reduce Contouring Variability of the Prostate?
Usmani, Nawaid, E-mail: email@example.com [Department of Radiation Oncology, Cross Cancer Institute, Edmonton, AB (Canada); Department of Oncology, University of Alberta, Edmonton, AB (Canada); Sloboda, Ron [Department of Oncology, University of Alberta, Edmonton, AB (Canada); Department of Medical Physics, Cross Cancer Institute, Edmonton, AB (Canada); Kamal, Wafa [Department of Radiation Oncology, Cross Cancer Institute, Edmonton, AB (Canada); Ghosh, Sunita [Department of Oncology, University of Alberta, Edmonton, AB (Canada); Department of Experimental Oncology, Cross Cancer Institute, Edmonton, AB (Canada); Pervez, Nadeem; Pedersen, John; Yee, Don; Danielson, Brita; Murtha, Albert; Amanie, John [Department of Radiation Oncology, Cross Cancer Institute, Edmonton, AB (Canada); Department of Oncology, University of Alberta, Edmonton, AB (Canada); Monajemi, Tara [Department of Medical Physics, Cross Cancer Institute, Edmonton, AB (Canada)
Purpose: The objective of this study is to determine whether there is less contouring variability of the prostate using higher-strength magnetic resonance images (MRI) compared with standard MRI and computed tomography (CT). Methods and Materials: Forty patients treated with prostate brachytherapy were accrued to a prospective study that included the acquisition of 1.5-T MR and CT images at specified time points. A subset of 10 patients had additional 3.0-T MR images acquired at the same time as their 1.5-T MR scans. Images from each of these patients were contoured by 5 radiation oncologists, with a random subset of patients repeated to quantify intraobserver contouring variability. To minimize bias in contouring the prostate, the image sets were placed in folders in a random order with all identifiers removed from the images. Results: Although there was less interobserver contouring variability in the overall prostate volumes in 1.5-T MRI compared with 3.0-T MRI (p < 0.01), there was no significant differences in contouring variability in the different regions of the prostate between 1.5-T MRI and 3.0-T MRI. MRI demonstrated significantly less interobserver contouring variability in both 1.5-T and 3.0-T compared with CT in overall prostate volumes (p < 0.01, p = 0.01), with the greatest benefits being appreciated in the base of the prostate. Overall, there was less intraobserver contouring variability than interobserver contouring variability for all of the measurements analyzed. Conclusions: Use of 3.0-T MRI does not demonstrate a significant improvement in contouring variability compared with 1.5-T MRI, although both magnetic strengths demonstrated less contouring variability compared with CT.
A.Fabich, CERN Metal Jet in a High Magnetic Field
McDonald, Kirk
.Fabich, CERN Slide 3 Setup Arrangement Observation area Calibration grid nozzle Ideal mercury jet We only look at data from 4.Akt, June 2002, 20 Tesla solenoid #12;A.Fabich, CERN Slide 4 In/Output variables Ę B-field 20 Tesla Ę Driving pressure 75 bar Ę Nozzle position Ę Nozzle type 0║/6║ (short/long) Ę Observation
Are Cluster Magnetic Fields Primordial ?
Robi Banerjee; Karsten Jedamzik
We present results of a detailed and fully non-linear numerical and analytical investigation of magnetic field evolution from the very earliest cosmic epochs to the present. We find that, under reasonable assumptions concerning the efficiency of a putative magnetogenesis era during cosmic phase transitions, surprisingly strong magnetic fields 10^{-13} - 10^{-11} Gauss, on comparatively small scales 100 pc - 10 kpc may survive to the present. Building on prior work on the evolution of magnetic fields during the course of gravitational collapse of a cluster, which indicates that pre-collapse fields of 4\\times 10^{-12} Gauss extant on small scales may suffice to produce clusters with acceptable Faraday rotation measures, we question the widely hold view that cluster magnetic fields may not be entirely of primordial origin.
Determination of Electric-Field, Magnetic-Field, and Electric...
Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)
Electric-Field, Magnetic-Field, and Electric-Current Distributions of Infrared Optical Antennas: A Near-Field Determination of Electric-Field, Magnetic-Field, and Electric-Current...
High resolution low-temperature superconductivity superconducting quantum interference device microscope for imaging magnetic fields
Weiss, Benjamin P.
-temperature superconducting niobium wire coupled to the input circuit of a superconducting quantum interference device SQUID-stated advantages of high-temperature superconductivity HTS over the more advanced low- temperature superconductivity LTS is that the higher oper- ating temperature, typically around 77 K, allows HTS SQUIDs
HE0241-0155 - Evidence for a large scale homogeneous field in a highly magnetic white dwarf
Dieter Reimers; Stefan Jordan; Norbert Christlieb
In the course of the Hamburg/ESO survey we have discovered a white dwarf whose spectrum exhibits many similarities with the prototype of magnetic white dwarfs Grw+70$^{\\circ}$8247. In particular several stationary line components indicative for magnetic fields between about 150 and 400 MG are found in both objects. However, the features between 5000 and 5500 \\AA in the spectrum of HE0241-0155 cannot be explained by stationary line components and demand a relatively homogeneous magnetic field with clustering around 200 MG. For this reason a pure dipole model failed to reproduce this spectral region.An offset-dipole configuration led to some improvement in the fit but a good agreement was only possible for a geometry -- described by an expansion into spherical harmonics -- where most of the surface is covered with magnetic field strengths strongly clustered around 200 MG. This may indicate the presence of a large magnetic spot whose presence could be tested with time resolved spectro-polarimetry.
Optical sensor of magnetic fields
Butler, M.A.; Martin, S.J.
An optical magnetic field strength sensor for measuring the field strength of a magnetic field comprising a dilute magnetic semi-conductor probe having first and second ends, longitudinally positioned in the magnetic field for providing Faraday polarization rotation of light passing therethrough relative to the strength of the magnetic field. Light provided by a remote light source is propagated through an optical fiber coupler and a single optical fiber strand between the probe and the light source for providing a light path therebetween. A polarizer and an apparatus for rotating the polarization of the light is provided in the light path and a reflector is carried by the second end of the probe for reflecting the light back through the probe and thence through the polarizer to the optical coupler. A photo detector apparatus is operably connected to the optical coupler for detecting and measuring the intensity of the reflected light and comparing same to the light source intensity whereby the magnetic field strength may be calculated.
Lightweight Superconducting Cables for use with High-Field Magnets and
Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)
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A Study to Develop an Industrial-Scale, Computer-Controlled High Magnetic Field Processing (HMFP) System to Assist in Commercializing the Novel, Enabling HMFP Manufacturing Technology
Lutdka, G. M.; Chourey, A. (American Magnetics, Inc.)
As the original magnet designer and manufacturer of ORNLÆs 9T, 5-inch ID bore magnet, American Magnetics Inc. (AMI) has collaborated with ORNLÆs Materials Processing GroupÆs and this partnership has been instrumental in the development of our unique thermo-magnetic facilities and expertise. Consequently, AMI and ORNL have realized that the commercial implementation of the High Magnetic Field Processing (HMFP) technology will require the evolution of robust, automated superconducting (SC) magnet systems that will be cost-effective and easy to operate in an industrial environment. The goal of this project and CRADA is to significantly expedite the timeline for implementing this revolutionary and pervasive cross-cutting technology for future US produced industrial components. The successful completion of this project is anticipated to significantly assist in the timely commercialization and licensing of our HMFP intellectual property for a broad spectrum of industries; and to open up a new market for AMI. One notable outcome of this project is that the ThermoMagnetic Processing Technology WON a prestigious 2009 R&D 100 Awards. This award acknowledges and recognizes our TMP Technology as one of the top 100 innovative US technologies in 2009. By successfully establishing the design requirements for a commercial scale magnetic processing system, this project effort has accomplished a key first step in facilitating the building and demonstration of a superconducting magnetic processing coil, enabling the transition of the High Magnetic Field Processing Technology beyond a laboratory novelty into a commercially viable and industrially scalable Manufacturing Technology.
Magnetic nanoparticles for applications in oscillating magnetic field
Peeraphatdit, Chorthip
Enzymatic and thermochemical catalysis are both important industrial processes. However, the thermal requirements for each process often render them mutually exclusive: thermochemical catalysis requires high temperature that denatures enzymes. One of the long-term goals of this project is to design a thermocatalytic system that could be used with enzymatic systems in situ to catalyze reaction sequences in one pot; this system would be useful for numerous applications e.g. conversion of biomass to biofuel and other commodity products. The desired thermocatalytic system would need to supply enough thermal energy to catalyze thermochemical reactions, while keeping the enzymes from high temperature denaturation. Magnetic nanoparticles are known to generate heat in an oscillating magnetic field through mechanisms including hysteresis and relaxational losses. We envisioned using these magnetic nanoparticles as the local heat source embedded in sub-micron size mesoporous support to spatially separate the particles from the enzymes. In this study, we set out to find the magnetic materials and instrumental conditions that are sufficient for this purpose. Magnetite was chosen as the first model magnetic material in this study because of its high magnetization values, synthetic control over particle size, shape, functionalization and proven biocompatibility. Our experimental designs were guided by a series of theoretical calculations, which provided clues to the effects of particle size, size distribution, magnetic field, frequency and reaction medium. Materials of theoretically optimal size were synthesized, functionalized, and their effects in the oscillating magnetic field were subsequently investigated. Under our conditions, the materials that clustered e.g. silica-coated and PNIPAM-coated iron oxides exhibited the highest heat generation, while iron oxides embedded in MSNs and mesoporous iron oxides exhibited the least bulk heating. It is worth noting that the specific loss power of PNIPAM-coated Fe{sub 3}O{sub 4} was peculiarly high, and the heat loss mechanism of this material remains to be elucidated. Since thermocatalysis is a long-term goal of this project, we also investigated the effects of the oscillating magnetic field system for the synthesis of 7-hydroxycoumarin-3-carboxylic acid. Application of an oscillating magnetic field in the presence of magnetic particles with high thermal response was found to effectively increase the reaction rate of the uncatalyzed synthesis of the coumarin derivative compared to the room temperature control.
High magnetic field studies of charged exciton localization in GaAs/Al{sub x}Ga{sub 1?x}As quantum wells
Jadczak, J.; Bryja, L., E-mail: email@example.com; Ryczko, K.; Kubisa, M.; W¾js, A. [Institute of Physics, Wroc?aw University of Technology, 50-370 Wroclaw (Poland); Potemski, M. [Laboratoire National des Champs Magnķtiques Intenses, CNRS-UJF-UPS-INSA, Grenoble (France); Liu, F. [Experimentelle Physik 2, Technische Universitõt Dortmund, D-44221 Dortmund (Germany); Yakovlev, D. R.; Bayer, M. [Experimentelle Physik 2, Technische Universitõt Dortmund, D-44221 Dortmund (Germany); Ioffe Physical-Technical Institute, Russian Academy of Sciences, 194021 St. Petersburg (Russian Federation); Nicoll, C. A.; Farrer, I.; Ritchie, D. A. [Cavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge, CB3 OHE (United Kingdom)
We report on low temperature, polarization resolved, high magnetic field (up to 23?T) photoluminescence experiments on high mobility asymmetric GaAs quantum wells. At high magnetic fields, we detect two strong emission lines of the neutral and positively charged excitons (X and X{sup +}) and a series of weaker lines of the excitons bound to ionized acceptors (AX{sup ?}). From polarization energy splittings of these lines, we determine the hole Landķ factors (g{sub h}) of different complexes. For X and X{sup +}, g{sub h} initially grows with magnetic field and then saturates at g{sub h}?=?0.88 and 1.55, respectively; for AX{sup ?}'s, g{sub h} begins from a high value (from 6 to 11 at zero field) and decreases with the field growth. This contrasting behavior is traced to the structure of valence band Landau levels, calculated numerically in the Luttinger model, beyond axial approximation. This points to the coexistence (in the same well) of mobile X and X{sup +} with localized and interface-pressed AX{sup ?} states.
Studies of Nb3Sn Strands Based on the Restacked-Rod Process for High-Field Accelerator Magnets Nb3Sn
DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)
Barzi, E; Bossert, M; Gallo, G; Lombardo, V; Turrioni, D; Yamada, R; Zlobin, A V
A major thrust in Fermilab's accelerator magnet R&D program is the development of Nb3Sn wires which meet target requirements for high field magnets, such as high critical current density, low effective filament size, and the capability to withstand the cabling process. The performance of a number of strands with 150/169 restack design produced by Oxford Superconducting Technology was studied for round and deformed wires. To optimize the maximum plastic strain, finite element modeling was also used as an aid in the design. Results of mechanical, transport and metallographic analyses are presented for round and deformed wires.
Magnetic Resonance Imaging System Based on Earth's Magnetic Field
Stepi?nik, Janez
Magnetic Resonance Imaging System Based on Earth's Magnetic Field Ales Mohoric,1,* Gorazd Planinsic magnetic field can be partly compensated by the receiving coil design and shielding of electromagnetic pick and must be monitored accurately.[8Ł 10] The importance of NMR in a non-uniform magnetic field
The Use of Small Coolers in a Magnetic Field
Green, Michael A.; Witte, Holger
Small 4 K coolers are used to cool superconducting magnets.These coolers are usually used with high temperature suerconductor (HTS)leads. In most cases, magnet is shielded with iron or active shieldcoils. Thus the field at the cooler is low. There are instances when thecooler must be in a magnetic field. Gifford McMahon (GM) coolers or pulsetube coolers are commercially available to cool the magnets. This paperwill discuss how the two types of coolers are affected by the straymagnetic field. Strategies for using coolers on magnets that generatestray magnetic fields are discussed.
Magnetic field measurements on the sun and implications for stellar magnetic field observations
Sun, W.H.; Giampapa, M.S.; Worden, S.P.
Results of solar magnetic field measurements in plages, sunspot umbrae, and sunspot penumbrae using high spectral resolution, unpolarized infrared H band spectral data are presented. A Fourier deconvolution analysis scheme similar to that utilized for stellar magnetic field measurements is adopted. As an example, a field strength of 3240 + or - 450 G is determined in a sunspot umbra combined with a value of 2000 + or - 180 G in the associated penumbra. These values are compared with a direct measurement of the spot umbra and penumbra field strengths based on the observed separation of the Zeeman components of the magnetically sensitive lines. Possible origins for the discrepancy between the results inferred by these two different techniques are discussed. The Fourier analysis results confirm the widespread occurrence of kilogauss level fields in the solar photosphere. The implications of the solar results for stellar magnetic field measurements are considered. 45 references.
Fast, High Fidelity Quantum Dot Spin Initialization without a Strong Magnetic Field by Two-Photon Processes
Arka Majumdar; Ziliang Lin; Andrei Faraon; Jelena Vuckovic
We describe a proposal for fast electron spin initialization in a negatively charged quantum dot coupled to a microcavity without the need for a strong magnetic field. We employ two-photon excitation to access trion states that are spin forbidden by one-photon excitation. Our simulation shows a maximum initialization speed of 1.3 GHz and maximum fidelity of 99.7% with realistic system parameters.
High field gradient particle accelerator
Nation, J.A.; Greenwald, S.
A high electric field gradient electron accelerator utilizing short duration, microwave radiation, and capable of operating at high field gradients for high energy physics applications or at reduced electric field gradients for high average current intermediate energy accelerator applications is disclosed. Particles are accelerated in a smooth bore, periodic undulating waveguide, wherein the period is so selected that the particles slip an integral number of cycles of the r.f. wave every period of the structure. This phase step of the particles produces substantially continuous acceleration in a traveling wave without transverse magnetic or other guide means for the particle. 10 figs.
High field gradient particle accelerator
Nation, John A. (Ithaca, NY); Greenwald, Shlomo (Haifa, IL)
A high electric field gradient electron accelerator utilizing short duration, microwave radiation, and capable of operating at high field gradients for high energy physics applications or at reduced electric field gradients for high average current intermediate energy accelerator applications. Particles are accelerated in a smooth bore, periodic undulating waveguide, wherein the period is so selected that the particles slip an integral number of cycles of the r.f. wave every period of the structure. This phase step of the particles produces substantially continuous acceleration in a traveling wave without transverse magnetic or other guide means for the particle.
Thermalization in External Magnetic Field
Ali-Akbari, Mohammad
In the AdS/CFT framework meson thermalization in the presence of a constant external magnetic field in a strongly coupled gauge theory has been studied. In the gravitational description the thermalization of mesons corresponds to the horizon formation on the flavour D7-brane which is embedded in the AdS_5 x S^5 background in the probe limit. The apparent horizon forms due to the time-dependent change in the baryon number chemical potential, the injection of baryons in the gauge theory. We will numerically show that the thermalization happens even faster in the presence of the magnetic field on the probe brane. We observe that this reduction in the thermalization time sustains up to a specific value of the magnetic field.
Microstructural Modification of a Cast Iron by Magnetic Field Processing
Kenik, Edward A [ORNL; Ludtka, Gail Mackiewicz- [ORNL; Ludtka, Gerard Michael [ORNL; Wilgen, John B [ORNL; Kisner, Roger A [ORNL
The current study deals with the microstructural modification of a nodular cast iron during solidification under the influence of high magnetic fields (up to 18 tesla).
600-T Magnetic Fields due to Cold Electron Flow in a simple Cu-Coil irradiated by High Power Laser pulses
Zhu, Baojun; Yuan, Dawei; Li, Yanfei; Li, Fang; Liao, Guoqian; Zhao, Jiarui; Zhong, Jiayong; Xue, Feibiao; Wei, Huigang; Zhang, Kai; Han, Bo; Pei, Xiaoxing; Liu, Chang; Zhang, Zhe; Wang, Weimin; Zhu, Jianqiang; Zhao, Gang; Zhang, Jie
A new simple mechanism due to cold electron flow to produce strong magnetic field is proposed. A 600-T strong magnetic field is generated in the free space at the laser intensity of 5.7x10^15 Wcm^-2. Theoretical analysis indicates that the magnetic field strength is proportional to laser intensity. Such a strong magnetic field offers a new experimental test bed to study laser-plasma physics, in particular, fast-ignition laser fusion research and laboratory astrophysics.
Magnetic fields in Neutron Stars
Vigan", Daniele; Miralles, Juan A; Rea, Nanda
Isolated neutron stars show a diversity in timing and spectral properties, which has historically led to a classification in different sub-classes. The magnetic field plays a key role in many aspects of the neutron star phenomenology: it regulates the braking torque responsible for their timing properties and, for magnetars, it provides the energy budget for the outburst activity and high quiescent luminosities (usually well above the rotational energy budget). We aim at unifying this observational variety by linking the results of the state-of-the-art 2D magneto-thermal simulations with observational data. The comparison between theory and observations allows to place two strong constraints on the physical properties of the inner crust. First, strong electrical currents must circulate in the crust, rather than in the star core. Second, the innermost part of the crust must be highly resistive, which is in principle in agreement with the presence of a novel phase of matter so-called nuclear pasta phase.
The Need For High Resolution In Studies Of The 3-D Magnetic Field Structure Of AGN Jets
Shane P. O'Sullivan; Denise C. Gabuzda
We are using "broadband" (4.6 to 43 GHz) multi-frequency VLBA polarization observations of compact AGN to investigate the 3-D structure of their jet magnetic (B) fields. Observing at several frequencies, separated by short and long intervals, enables reliable determination of the distribution of Faraday Rotation, and thereby the intrinsic B field structure. Transverse Rotation Measure (RM) gradients were detected in the jets of 0954+658 and 1418+546, providing evidence for the presence of a helical B field surrounding the jet. The RM in the core regions of 2200+420 (BL Lac), 0954+658 and 1418+546 display different signs in different frequency-intervals (on different spatial scales); we suggest an explanation for this in terms of modest bends in a helical B field surrounding their jets. In future, polarization observations with a combination of VSOP-2 at 8, 22 and 43 GHz and ground arrays at frequencies with corresponding resolution will help map out the distributions of Faraday rotation, spectral index and the 3-D B field structure both across the jet and closer to the central engine, providing strong constraints for any jet B field models.
Design and performance of an ultra-high vacuum scanning tunneling microscope operating at dilution refrigerator temperatures and high magnetic fields
Misra, Shashank; Drozdov, Ilya K; Seo, Jungpil; Gyenis, Andras; Kingsley, Simon C J; Jones, Howard; Yazdani, Ali
We describe the construction and performance of a scanning tunneling microscope (STM) capable of taking maps of the tunneling density of states with sub-atomic spatial resolution at dilution refrigerator temperatures and high (14 T) magnetic fields. The fully ultra-high vacuum system features visual access to a two-sample microscope stage at the end of a bottom-loading dilution refrigerator, which facilitates the transfer of in situ prepared tips and samples. The two-sample stage enables location of the best area of the sample under study and extends the experiment lifetime. The successful thermal anchoring of the microscope, described in detail, is confirmed through a base temperature reading of 20 mK, along with a measured electron temperature of 250 mK. Atomically-resolved images, along with complementary vibration measurements, are presented to confirm the effectiveness of the vibration isolation scheme in this instrument. Finally, we demonstrate that the microscope is capable of the same level of perform...
Development and applications of NMR (nuclear magnetic resonance) in low fields and zero field
Bielecki, A.
This dissertation is about nuclear magnetic resonance (NMR) spectroscopy in the absence of applied magnetic fields. NMR is usually done in large magnetic fields, often as large as can be practically attained. The motivation for going the opposite way, toward zero field, is that for certain types of materials, particularly powdered or polycrystalline solids, the NMR spectra in zero field are easier to interpret than those obtained in high field. 92 refs., 60 figs., 1 tab.
National High Magnetic Field Laboratory 2010 ANNUAL REPORTFlorida State University University of Florida Los Alamos National Lab
Weston, Ken
RESEARCH HIGHLIGHTS: CONDENSED MATTER SCIENCE Technique development, graphene, magnetism & magnetic tenth year of operation, continued its essential role in graphene exploration. Interest has also
Turbulence and Magnetic Fields in Clouds
Shantanu Basu
We discuss several categories of models which may explain the IMF, including the possible role of turbulence and magnetic fields.
Probes for investigating the effect of magnetic field, field orientation, temperature and strain on the critical current density of anisotropic high-temperature superconducting tapes in a split-pair 15 T horizontal magnet
Sunwong, P.; Higgins, J. S.; Hampshire, D. P. [Superconductivity Group, Centre for Materials Physics, Department of Physics, University of Durham, Durham DH1 3LE (United Kingdom)
We present the designs of probes for making critical current density (J{sub c}) measurements on anisotropic high-temperature superconducting tapes as a function of field, field orientation, temperature and strain in our 40 mm bore, split-pair 15 T horizontal magnet. Emphasis is placed on the design of three components: the vapour-cooled current leads, the variable temperature enclosure, and the springboard-shaped bending beam sample holder. The vapour-cooled brass critical-current leads used superconducting tapes and in operation ran hot with a duty cycle (D) of ?0.2. This work provides formulae for optimising cryogenic consumption and calculating cryogenic boil-off, associated with current leads used to make J{sub c} measurements, made by uniformly ramping the current up to a maximum current (I{sub max}) and then reducing the current very quickly to zero. They include consideration of the effects of duty cycle, static helium boil-off from the magnet and Dewar (b{sup ?}), and the maximum safe temperature for the critical-current leads (T{sub max}). Our optimized critical-current leads have a boil-off that is about 30% less than leads optimized for magnet operation at the same maximum current. Numerical calculations show that the optimum cross-sectional area (A) for each current lead can be parameterized by LI{sub max}/A=[1.46D{sup ?0.18}L{sup 0.4}(T{sub max}?300){sup 0.25D{sup ?{sup 0{sup .{sup 0{sup 9}}}}}}+750(b{sup ?}/I{sub max})D{sup 10{sup ?{sup 3I{sub m}{sub a}{sub x}?2.87b{sup ?}}}}]ū 10{sup 6}A m{sup ?1} where L is the current lead's length and the current lead is operated in liquid helium. An optimum A of 132 mm{sup 2} is obtained when I{sub max} = 1000 A, T{sub max} = 400 K, D = 0.2, b{sup ?} = 0.3 l?h{sup ?1} and L = 1.0 m. The optimized helium consumption was found to be 0.7 l?h{sup ?1}. When the static boil-off is small, optimized leads have a boil-off that can be roughly parameterized by: b/I{sub max?} ? (1.35 ū 10{sup ?3})D{sup 0.41} l?h{sup ?1}?A{sup ?1}. A split-current-lead design is employed to minimize the rotation of the probes during the high current measurements in our high-field horizontal magnet. The variable-temperature system is based on the use of an inverted insulating cup that operates above 4.2 K in liquid helium and above 77.4 K in liquid nitrogen, with a stability of ▒80 mK to ▒150 mK. Uniaxial strains of ?1.4% to 1.0% can be applied to the sample, with a total uncertainty of better than ▒0.02%, using a modified bending beam apparatus which includes a copper beryllium springboard-shaped sample holder.
White, Stephen
Chapter 5 CORONAL MAGNETIC FIELD MEASUREMENTS THROUGH GYRORESONANCE EMISSION Stephen M. White This article reviews the use of gyroresonance emission at radio wavelengths to measure coronal magnetic fields. Keywords: Sun, solar corona, solar magnetic fields, solar radio emission Introduction Since the realization
Ng, C.-Y.; Kaspi, V. M. [Department of Physics, McGill University, Montreal, QC H3A 2T8 (Canada); Ho, W. C. G. [School of Mathematics, University of Southampton, Southampton SO17 1BJ (United Kingdom); Weltevrede, P. [Jodrell Bank Centre for Astrophysics, University of Manchester, Alan Turing Building, Manchester M13 9PL (United Kingdom); Bogdanov, S. [Columbia Astrophysics Laboratory, Columbia University, 550 West 120th Street, New York, NY 10027 (United States); Shannon, R. [CSIRO Astronomy and Space Sciences, Australia Telescope National Facility, Marsfield, NSW 2210 (Australia); Gonzalez, M. E., E-mail: email@example.com [Department of Physics and Astronomy, University of British Columbia, Vancouver, BC V6T 1Z1 (Canada)
High-magnetic-field radio pulsars are important transition objects for understanding the connection between magnetars and conventional radio pulsars. We present a detailed study of the young radio pulsar J1119-6127, which has a characteristic age of 1900 yr and a spin-down-inferred magnetic field of 4.1 Multiplication-Sign 10{sup 13} G, and its associated supernova remnant G292.2-0.5, using deep XMM-Newton and Chandra X-ray Observatory exposures of over 120 ks from each telescope. The pulsar emission shows strong modulation below 2.5 keV with a single-peaked profile and a large pulsed fraction of 0.48 {+-} 0.12. Employing a magnetic, partially ionized hydrogen atmosphere model, we find that the observed pulse profile can be produced by a single hot spot of temperature 0.13 keV covering about one-third of the stellar surface, and we place an upper limit of 0.08 keV for an antipodal hot spot with the same area. The non-uniform surface temperature distribution could be the result of anisotropic heat conduction under a strong magnetic field, and a single-peaked profile seems common among high-B radio pulsars. For the associated remnant G292.2-0.5, its large diameter could be attributed to fast expansion in a low-density wind cavity, likely formed by a Wolf-Rayet progenitor, similar to two other high-B radio pulsars.
A Braking Index for the Young, High-Magnetic-Field, Rotation-Powered Pulsar in Kes 75
Margaret A. Livingstone; Victoria M. Kaspi; E. V. Gotthelf; Lucien Kuiper
We present the first phase-coherent measurement of a braking index for the young, energetic rotation-powered pulsar PSR J1846-0258. This 324 ms pulsar is located at the center of the supernova remnant Kes 75 and has a characteristic age of tau_c = 723 years, a spin-down energy of 8.3x10^{36}erg/s, and inferred magnetic field of 4.9x10^{13} G. Two independent phase-coherent timing solutions are derived which together span 5.5 yr of data obtained with the Rossi X-ray Timing Explorer. In addition, a partially phase-coherent timing analysis confirms the fully phase-coherent result. The measured value of the braking index, n=2.65+/-0.01, is significantly less than 3, the value expected from magnetic dipole radiation, implying another physical process must contribute to the pulsar's rotational evolution. Assuming the braking index has been constant since birth, we place an upper limit on the spin-down age of J1846-0258 of 884 yr, the smallest age estimate of any rotation-powered pulsar.
Magnetic monopole and the nature of the static magnetic field
Xiuqing Huang
We investigate the factuality of the hypothetical magnetic monopole and the nature of the static magnetic field. It is shown from many aspects that the concept of the massive magnetic monopoles clearly is physically untrue. We argue that the static magnetic field of a bar magnet, in fact, is the static electric field of the periodically quasi-one-dimensional electric-dipole superlattice, which can be well established in some transition metals with the localized d-electron. This research may shed light on the perfect unification of magnetic and electrical phenomena.
Magnets made with high-temperature superconducting (HTS) coils operating at low temperatures have the potential to produce extremely high fields for use in accelerators and beam lines. The specific application of interest that we are proposing is to use a very high field (of the order of 50 Tesla) solenoid to provide a very small beta region for the final stages of cooling for a muon collider. With the commercial availability of HTS conductor based on BSCCO technology with high current carrying capacity at 4.2 K, very high field solenoid magnets should be possible. In this paper we will evaluate the technical issues associated with building this magnet. In particular we address how to mitigate the high Lorentz stresses associated with this high field magnet.
Electro-Mechanical Resonant Magnetic Field Sensor
Temnykh, A B; Temnykh, Alexander B.; Lovelace, Richard V. E.
We describe a new type of magnetic field sensor which is termed an Electro-Mechanical Resonant Sensor (EMRS). The key part of this sensor is a small conductive elastic element with low damping rate and therefore a high Q fundamental mode of frequency $f_1$. An AC current is driven through the elastic element which, in the presence of a magnetic field, causes an AC force on the element. When the frequency of the AC current matches the resonant frequency of the element, maximum vibration of the element occurs and this can be measured precisely by optical means. We have built and tested a model sensor of this type using for the elastic element a length of copper wire of diameter 0.030 mm formed into a loop shape. The wire motion was measured using a light emitting diode photo-transistor assembly. This sensor demonstrated a sensitivity better than 0.001G for an applied magnetic field of $ \\sim 1$G and a good selectivity for the magnetic field direction. The sensitivity can be easily improved by a factor of $\\sim ...
Matching field effects at tesla-level magnetic fields in critical current density in high-Tc superconductors containing self-assembled columnar defects
Sinclair, J. [University of Tennessee, Knoxville (UTK); Zuev, Yuri L [ORNL; Cantoni, Claudia [ORNL; Wee, Sung Hun [ORNL; Varanasi, C. V. [University of Dayton Research Institute; Thompson, James R [ORNL; Christen, David K [ORNL
We have investigated the superconductive transport properties of YBa2Cu3O7 films containing self-assembled columnar arrays of second phase SrZrO3 or BaSnO3 precipitates. A matching condition between columnar pinning sites (aligned at or near the c axis) and external magnetic flux, tilted with respect to them, is identified in the critical current JC.H/ data. The results for the material containing SrZrO3-based pins are analyzed within a simple intuitive model. At matching, the critical current is enhanced above the model prediction. In complementary contact-free investigations of BaSnO3-doped material, matching effects are observed over a wide range of temperatures in the field dependence of JC.H/. The deduced matching fields agree reasonably well with the densities of columnar pins directly observed by scanning electron microscopy.
Permanent Magnet Ecr Plasma Source With Magnetic Field Optimization
Doughty, Frank C. (Plano, TX); Spencer, John E. (Plano, TX)
In a plasma-producing device, an optimized magnet field for electron cyclotron resonance plasma generation is provided by a shaped pole piece. The shaped pole piece adjusts spacing between the magnet and the resonance zone, creates a convex or concave resonance zone, and decreases stray fields between the resonance zone and the workpiece. For a cylindrical permanent magnet, the pole piece includes a disk adjacent the magnet together with an annular cylindrical sidewall structure axially aligned with the magnet and extending from the base around the permanent magnet. The pole piece directs magnetic field lines into the resonance zone, moving the resonance zone further from the face of the magnet. Additional permanent magnets or magnet arrays may be utilized to control field contours on a local scale. Rather than a permeable material, the sidewall structure may be composed of an annular cylindrical magnetic material having a polarity opposite that of the permanent magnet, creating convex regions in the resonance zone. An annular disk-shaped recurve section at the end of the sidewall structure forms magnetic mirrors keeping the plasma off the pole piece. A recurve section composed of magnetic material having a radial polarity forms convex regions and/or magnetic mirrors within the resonance zone.
Magnetic fluid flow phenomena in DC and rotating magnetic fields
Rhodes, Scott E. (Scott Edward), 1981-
An investigation of magnetic fluid experiments and analysis is presented in three parts: a study of magnetic field induced torques in magnetorheological fluids, a characterization and quantitative measurement of properties ...
Supported by the National Science Foundation and the State of Florida 1 REPORTSNATIONAL HIGH MAGNETIC FIELD LABORATORY
Weston, Ken
.S. Shvindlerman3 Magnetic Driving Force cont. on page 6 N H M F L M a g n e t s Engineered for Unique Needs and Sometimes Unworldly Destinations In the first years of the laboratory, NHMFL magnet engineers, designers of magnets engineered to the specific needs of customers. Typically when crystals are grown, the presence
Baryon onset in a magnetic field
Alexander Haber; Florian Preis; Andreas Schmitt
The critical baryon chemical potential for the onset of nuclear matter is a function of the vacuum mass and the binding energy. Both quantities are affected by an external magnetic field. We show within two relativistic mean-field models - including magnetic catalysis, but omitting the anomalous magnetic moment - that a magnetic field increases both the vacuum mass and the binding energy. For sufficiently large magnetic fields, the effect on the vacuum mass dominates and as a result the critical baryon chemical potential is increased.
Developments in deep brain stimulation using time dependent magnetic fields
Crowther, L.J.; Nlebedim, I.C.; Jiles, D.C.
The effect of head model complexity upon the strength of field in different brain regions for transcranial magnetic stimulation (TMS) has been investigated. Experimental measurements were used to verify the validity of magnetic field calculations and induced electric field calculations for three 3D human head models of varying complexity. Results show the inability for simplified head models to accurately determine the site of high fields that lead to neuronal stimulation and highlight the necessity for realistic head modeling for TMS applications.
Bipolar pulse field for magnetic refrigeration
Lubell, Martin S. (Oak Ridge, TN)
A magnetic refrigeration apparatus includes first and second steady state magnets, each having a field of substantially equal strength and opposite polarity, first and second bodies made of magnetocaloric material disposed respectively in the influence of the fields of the first and second steady state magnets, and a pulsed magnet, concentric with the first and second steady state magnets, and having a field which cycles between the fields of the first and second steady state magnets, thereby cyclically magnetizing and demagnetizing and thus heating and cooling the first and second bodies. Heat exchange apparatus of suitable design can be used to expose a working fluid to the first and second bodies of magnetocaloric material. A controller is provided to synchronize the flow of working fluid with the changing states of magnetization of the first and second bodies.
Bipolar pulse field for magnetic refrigeration
Lubell, M.S.
A magnetic refrigeration apparatus includes first and second steady state magnets, each having a field of substantially equal strength and opposite polarity, first and second bodies made of magnetocaloric material disposed respectively in the influence of the fields of the first and second steady state magnets, and a pulsed magnet, concentric with the first and second steady state magnets, and having a field which cycles between the fields of the first and second steady state magnets, thereby cyclically magnetizing and demagnetizing and thus heating and cooling the first and second bodies. Heat exchange apparatus of suitable design can be used to expose a working fluid to the first and second bodies of magnetocaloric material. A controller is provided to synchronize the flow of working fluid with the changing states of magnetization of the first and second bodies. 2 figs.
HTS High Gradient Magnetic Separation system
Daugherty, M.A.; Coulter, J.Y.; Hults, W.L. [and others
We report on the assembly, characterization and operation of a high temperature superconducting (HTS) magnetic separator. The magnet is made of 624 m of Silver/BSCCO superconducting wire and has overall dimensions of 18 cm OD, 15.5 cm height and 5 cm ID. The HTS current leads are designed to operate with the warm end at 75 K and the cold end cooled by a two stage Gifford-McMahon cryocooler. The upper stage of the cryocooler cools the thermal shield and two heat pipe thermal intercepts. The lower stage of the cryocooler cools the HTS magnet and the bottom end of the HTS current leads. The HTS magnet was initially characterized in liquid cryogens. We report on the current- voltage (I-V) characteristics of the HTS magnet at temperatures ranging from 15 to 40 K. At 40 K the magnet can generate a central field of 2.0 T at a current of 120 A.
Magnetic field topology of accreting white dwarfs
Klaus Reinsch; Fabian Euchner; Klaus Beuermann; Stefan Jordan
We report first results of our systematic investigation of the magnetic field structure of rotating single magnetic white dwarfs and of white dwarfs in magnetic cataclysmic variables. The global magnetic field distributions on the isolated white dwarf HE1045-0908 and the accreting white dwarfs in EF Eri and CP Tuc have been derived from phase-resolved flux and polarization spectra obtained with FORS1 at the ESO VLT using the systematic method of Zeeman tomography.
DC-based magnetic field controller
Kotter, D.K.; Rankin, R.A.; Morgan, J.P.
A magnetic field controller is described for laboratory devices and in particular to dc operated magnetic field controllers for mass spectrometers, comprising a dc power supply in combination with improvements to a Hall probe subsystem, display subsystem, preamplifier, field control subsystem, and an output stage. 1 fig.
DC-based magnetic field controller
Kotter, Dale K. (Shelley, ID); Rankin, Richard A. (Ammon, ID); Morgan, John P,. (Idaho Falls, ID)
A magnetic field controller for laboratory devices and in particular to dc operated magnetic field controllers for mass spectrometers, comprising a dc power supply in combination with improvements to a hall probe subsystem, display subsystem, preamplifier, field control subsystem, and an output stage.
Supported by the National Science Foundation and the State of Florida 1 REPORTSNATIONAL HIGH MAGNETIC FIELD LABORATORY
Weston, Ken
National Laboratory Power Supplies Installed for Quasi-Continuous Magnet at LANL Power converters five 64 MW converters. The liquid nitrogen cooled magnet, which will be the most powerful of its class, to be completed later. Power Supply Design Each power converter is supplied with 21 kV from the 1430 MVA / 600 MJ
Spin-lattice coupling in uranium dioxide probed by magnetostriction measurements at high magnetic fields (P08358-E001-PF)
K. Gofryk; M. Jaime
Conclusions Our preliminary magnetostriction measurements have already shown a strong interplay of lattice dynamic and magnetism in both antiferromagnetic and paramagnetic states, and give unambiguous evidence of strong spin- phonon coupling in uranium dioxide. Further studies are planned to address the puzzling behavior of UO2 in magnetic and paramagnetic states and details of the spin-phonon coupling.
A Common Coil Magnet for Testing High Field Superconductors* , J.P. Cozzolino, M.A. Harrison, W.B. Sampson, P.J. Wanderer
Gupta, Ramesh
. The performance of the magnet is summarized along with test results from insert coils wound from N3 Sn ribbon racetrack shaped coils readily wound from high aspect ratio conductor. In this geometry the magnet has two coil magnet. The turns on the right form one half of the upper and lower dipoles, but are part
Primordial Magnetic Fields in False Vacuum Inflation
A. C. Davis; K. Dimopoulos
We show that, during false vacuum inflation, a primordial magnetic field can be created, sufficiently strong to seed the galactic dynamo and generate the observed galactic magnetic fields. Considering the inflaton dominated regime, our field is produced by the Higgs-field gradients, resulting from a grand unified phase transition. The evolution of the field is followed from its creation through to the epoch of structure formation, subject to the relevant constraints. We find that it is possible to create a magnetic field of sufficient magnitude, provided the phase transition occurs during the final 5 e-foldings of the inflationary period.
Magnetic fields in anisotropic relativistic stars
Vladimir Folomeev; Vladimir Dzhunushaliev
Relativistic, spherically symmetric configurations consisting of a gravitating magnetized anisotropic fluid are studied. For such configurations, we obtain static equilibrium solutions with an axisymmetric, poloidal magnetic field produced by toroidal electric currents. The presence of such a field results in small deviations of the shape of the configuration from spherical symmetry. This in turn leads to the modification of an equation for the current and correspondingly to changes in the structure of the internal magnetic field for the systems supported by the anisotropic fluid, in contrast to the case of an isotropic fluid, where such deviations do not affect the magnetic field.
Generation of the magnetic field in jets
V. Urpin
We consider dynamo action under the combined influence of turbulence and large-scale shear in sheared jets. Shear can stretch turbulent magnetic field lines in such a way that even turbulent motions showing mirror symmetry become suitable for generation of a large-scale magnetic field. We derive the integral induction equation governing the behaviour of the mean field in jets. The main result is that sheared jets may generate a large-scale magnetic field if shear is sufficiently strong. The generated mean field is mainly concentrated in a magnetic sheath surrounding the central region of a jet, and it exhibits sign reversals in the direction of the jet axis. Typically, the magnetic field in a sheath is dominated by the component along the jet that can reach equipartition with the kinetic energy of particles, The field in the central region of jets has a more disordered structure.
Color superconductivity in a strong external magnetic field
Cristina Manuel
We explore the effects of an applied strong external magnetic field in a three flavor massless color superconductor. The long-range component of the B field that penetrates the superconductor enhances some quark condensates, leading to a different condensation pattern. The external field also reduces the flavor symmetries in the system, and thus it changes drastically the corresponding low energy physics. Our considerations are relevant for the study of highly magnetized compact stars.
One-way Ponderomotive Barrier in a Uniform Magnetic Field
I.Y. Dodin; N.J. Fisch
The possibility of an asymmetric ponderomotive barrier in a nonuniform dc magnetic field by high-frequency radiation near the cyclotron resonance for selected plasma species was contemplated in Physics of Plasmas 11 (November 2004) 5046-5064. Here we show that a similar one-way barrier, which reflects particles incident from one side while transmitting those incident from the opposite side, can be produced also in a uniform magnetic field, entirely due to inhomogeneity of high-frequency drive.
Graphene Nanoribbon in Sharply Localized Magnetic Fields
Abdulaziz D. Alhaidari; Hocine Bahlouli; Abderrahim El Mouhafid; Ahmed Jellal
We study the effect of a sharply localized magnetic field on the electron transport in a strip (ribbon) of graphene sheet, which allows to give results for the transmission and reflection probability through magnetic barriers. The magnetic field is taken as a single and double delta type localized functions, which are treated later as the zero width limit of gaussian fields. For both field configurations, we evaluate analytically and numerically their transmission and reflection coefficients. The possibility of spacial confinement due to the inhomogeneous field configuration is also investigated.
Influence of Time-Varying External Magnetic Fields on Trapped Fields in Bulk Superconductors
Zou, Jin; Ainslie, Mark D.; Hu, Di; Cardwell, David A.
Large, single-grain bulk high-temperature superconductors (HTS) can trap magnetic fields over 17 T below 30 K and up to 3 T at 77 K, and have significant potential to replace permanent magnets, the fields from which are limited to significantly less...
PHYSICAL REVIEW B 88, 174406 (2013) High magnetic field study of the Tm2Fe17 and Tm2Fe17D3.2 compounds
Paris-Sud XI, Universitķ de
of the deuteride Tm2Fe17D3.2 has been carried out in steady (14 T) and pulsed (60 T and, in one case, up to 74 T in the deuteride. In either case the magnetization increases with magnetic field undulatorily in broad steps whose the powder data for the deuteride. Thus, the mean molecular field on Tm in Tm2Fe17D3.2 is found to be 49
Permanent magnet edge-field quadrupole
Tatchyn, Roman O. (Mountain View, CA)
Planar permanent magnet edge-field quadrupoles for use in particle accelerating machines and in insertion devices designed to generate spontaneous or coherent radiation from moving charged particles are disclosed. The invention comprises four magnetized rectangular pieces of permanent magnet material with substantially similar dimensions arranged into two planar arrays situated to generate a field with a substantially dominant quadrupole component in regions close to the device axis.
Magnetic-field sensing coil embedded in ceramic for measuring ambient magnetic field
Takahashi, Hironori
A magnetic pick-up coil for measuring magnetic field with high specific sensitivity, optionally with an electrostatic shield (24), having coupling elements (22) with high winding packing ratio, oriented in multiple directions, and embedded in ceramic material for structural support and electrical insulation. Elements of the coil are constructed from green ceramic sheets (200) and metallic ink deposited on surfaces and in via holes of the ceramic sheets. The ceramic sheets and the metallic ink are co-fired to create a monolithic hard ceramic body (20) with metallized traces embedded in, and placed on exterior surfaces of, the hard ceramic body. The compact and rugged coil can be used in a variety of environments, including hostile conditions involving ultra-high vacuum, high temperatures, nuclear and optical radiation, chemical reactions, and physically demanding surroundings, occurring either individually or in combinations.
Magnetic monopole field exposed by electrons
Bķchķ, A; Van Tendeloo, G; Verbeeck, J
Magnetic monopoles have provided a rich field of study, leading to a wide area of research in particle physics, solid state physics, ultra-cold gases, superconductors, cosmology, and gauge theory. So far, no true magnetic monopoles were found experimentally. Using the Aharonov-Bohm effect, one of the central results of quantum physics, shows however, that an effective monopole field can be produced. Understanding the effects of such a monopole field on its surroundings is crucial to its observation and provides a better grasp of fundamental physical theory. We realize the diffraction of fast electrons at a magnetic monopole field generated by a nanoscopic magnetized ferromagnetic needle. Previous studies have been limited to theoretical semiclassical optical calculations of the motion of electrons in such a monopole field. Solid state systems like the recently studied 'spin ice' provide a constrained system to study similar fields, but make it impossible to separate the monopole from the material. Free space ...
External-field-free magnetic biosensor
Li, Yuanpeng; Wang, Yi; Klein, Todd; Wang, Jian-Ping, E-mail: email@example.com [Department of Electrical and Computer Engineering, University of Minnesota, Minneapolis, Minnesota 55455 (United States)
In this paper, we report a magnetic nanoparticle (MNP) detection scheme without the presence of any external magnetic field. The proposed magnetic sensor uses a patterned groove structure within the sensor so that no external magnetic field is needed to magnetize the MNPs. An example is given based on a giant magnetoresistance (GMR) sensing device with a spin valve structure. For this structure, the detection of MNPs located inside the groove and near the free layer is demonstrated under no external magnetic field. Micromagnetic simulations are performed to calculate the signal to noise level of this detection scheme. A maximum signal to noise ratio (SNR) of 18.6?dB from one iron oxide magnetic nanoparticle with 8?nm radius is achieved. As proof of concept, this external-field-free GMR sensor with groove structure of 200?nm?ū?200?nm is fabricated using a photo and an electron beam integrated lithography process. Using this sensor, the feasibility demonstration of the detection SNR of 9.3?dB is achieved for 30??l magnetic nanoparticles suspension (30?nm iron oxide particles, 1?mg/ml). This proposed external-field-free sensor structure is not limited to GMR devices and could be applicable to other magnetic biosensing devices.
Magnetic Field Geometry in "Red" and "Blue" BL Lacs
P. Kharb; D. C. Gabuzda; P. Shastri
We compare the systematics of the magnetic field geometry in the "red" low-energy peaked BL Lacs (LBLs) and "blue" high-energy peaked BL Lacs (HBLs) using VLBI polarimetric images. The LBLs are primarily "radio--selected" BL Lacs and the HBLs are primarily "X-ray selected". In contrast to the LBLs, which show predominantly transverse jet magnetic fields, the HBLs show predominantly longitudinal fields. Thus, while the SED peaks of core-dominated quasars, LBLs and HBLs form a sequence of increasing frequency, the magnetic field geometry does not follow an analogous sequence. We briefly investigate possible connections between the observed parsec-scale magnetic field structures and circular polarization measurements in the literature on various spatial scales.
ECE 390 Electric & Magnetic Fields Catalog Description: Static and quasi-static electric and magnetic fields.
Engineering Magnetics, ECE 593 Structure: Three 80-minute lectures per week Instructors: A. Weisshaar (primaryECE 390 Ł Electric & Magnetic Fields Catalog Description: Static and quasi-static electric and magnetic fields. Credits: 4 Terms Offered: Fall Prerequisites: MTH 255, ENGR 203 (concurrent enrollment
Prospects for x-ray polarimetry measurements of magnetic fields in magnetized liner inertial fusion plasmas
Lynn, Alan G., E-mail: email@example.com; Gilmore, Mark [Department of Electrical and Computer Engineering, University of New Mexico, Albuquerque, New Mexico 87131 (United States)
Magnetized Liner Inertial Fusion (MagLIF) experiments, where a metal liner is imploded to compress a magnetized seed plasma may generate peak magnetic fields ?10{sup 4} T (100 Megagauss) over small volumes (?10{sup ?10}m{sup 3}) at high plasma densities (?10{sup 28}m{sup ?3}) on 100 ns time scales. Such conditions are extremely challenging to diagnose. We discuss the possibility of, and issues involved in, using polarimetry techniques at x-ray wavelengths to measure magnetic fields under these extreme conditions.
Constraining primordial magnetic fields with future cosmic shear surveys
Fedeli, C. [Department of Astronomy, University of Florida, 211 Bryant Space Science Center, Gainesville, FL 32611 (United States); Moscardini, L., E-mail: firstname.lastname@example.com, E-mail: firstname.lastname@example.com [Dipartimento di Astronomia, UniversitÓ di Bologna, Via Ranzani 1, 40127 Bologna (Italy)
The origin of astrophysical magnetic fields observed in galaxies and clusters of galaxies is still unclear. One possibility is that primordial magnetic fields generated in the early Universe provide seeds that grow through compression and turbulence during structure formation. A cosmological magnetic field present prior to recombination would produce substantial matter clustering at intermediate/small scales, on top of the standard inflationary power spectrum. In this work we study the effect of this alteration on one particular cosmological observable, cosmic shear. We adopt the semi-analytic halo model in order to describe the non-linear clustering of matter, and feed it with the altered mass variance induced by primordial magnetic fields. We find that the convergence power spectrum is, as expected, substantially enhanced at intermediate/small angular scales, with the exact amplitude of the enhancement depending on the magnitude and power-law index of the magnetic field power spectrum. Specifically, for a fixed amplitude, the effect of magnetic fields is larger for larger spectral indices. We use the predicted statistical errors for a future wide-field cosmic shear survey, on the model of the ESA Cosmic Vision mission Euclid, in order to forecast constraints on the amplitude of primordial magnetic fields as a function of the spectral index. We find that the amplitude will be constrained at the level of ? 0.1 nG for n{sub B} ? ?3, and at the level of ? 10{sup ?7} nG for n{sub B} ? 3. The latter is at the same level of lower bounds coming from the secondary emission of gamma-ray sources, implying that for high spectral indices Euclid will certainly be able to detect primordial magnetic fields, if they exist. The present study shows how large-scale structure surveys can be used for both understanding the origins of astrophysical magnetic fields and shedding new light on the physics of the pre-recombination Universe.
Transient horizontal magnetic fields in solar plage regions
R. Ishikawa; S. Tsuneta; K. Ichimoto; H. Isobe; Y. Katsukawa; B. W. Lites; S. Nagata; T. Shimizu; R. A. Shine; Y. Suematsu; T. D. Tarbell; A. M. Title
We report the discovery of isolated, small-scale emerging magnetic fields in a plage region with the Solar Optical Telescope aboard Hinode. Spectro-polarimetric observations were carried out with a cadence of 34 seconds for the plage region located near disc center. The vector magnetic fields are inferred by Milne-Eddington inversion. The observations reveal widespread occurrence of transient, spatially isolated horizontal magnetic fields. The lateral extent of the horizontal magnetic fields is comparable to the size of photospheric granules. These horizontal magnetic fields seem to be tossed about by upflows and downflows of the granular convection. We also report an event that appears to be driven by the magnetic buoyancy instability. We refer to buoyancy-driven emergence as type1 and convection-driven emergence as type2. Although both events have magnetic field strengths of about 600 G, the filling factor of type1 is a factor of two larger than that of type2. Our finding suggests that the granular convection in the plage regions is characterized by a high rate of occurrence of granular-sized transient horizontal fields.
Discovery of magnetic fields in hot subdwarfs
S. J. O'Toole; S. Jordan; S. Friedrich; U. Heber
We present polarisation measurements of sdB and sdO stars using FORS1 on the VLT. The observations were made as part of a project to determine whether magnetic fields in two super-metal-rich stars can explain their extreme abundance peculiarities. Field strengths of up to ~1.5 kG have been measured at varying levels of significance in each of our six targets, however no clear evidence was found between apparently normal subdwarfs and the metal-rich objects. The origin of the magnetic fields is unknown. We also discuss the implications of our measurements for magnetic flux conservation in late stages of stellar evolution.
Lithium pellet injection into high pressure magnetically confined plasmas
B÷se, Brock (Brock Darrel)
The ablation of solid pellets injected into high temperature magnetically confined plasmas is characterized by rapid oscillations in the ablation rate, and the formation of field aligned filaments in the ablatant. High ...
Influence of primordial magnetic fields on 21 cm emission
Dominik R. G. Schleicher; Robi Banerjee; Ralf S. Klessen
Magnetic fields in the early universe can significantly alter the thermal evolution and the ionization history during the dark ages. This is reflected in the 21 cm line of atomic hydrogen, which is coupled to the gas temperature through collisions at high redshifts, and through the Wouthuysen-Field effect at low redshifts. We present a semi-analytic model for star formation and the build-up of a Lyman alpha background in the presence of magnetic fields, and calculate the evolution of the mean 21 cm brightness temperature and its frequency gradient as a function of redshift. We further discuss the evolution of linear fluctuations in temperature and ionization in the presence of magnetic fields and calculate the effect on the 21 cm power spectrum. At high redshifts, the signal is increased compared to the non-magnetic case due to the additional heat input into the IGM from ambipolar diffusion and the decay of MHD turbulence. At lower redshifts, the formation of luminous objects and the build-up of a Lyman alpha background can be delayed by a redshift interval of 10 due to the strong increase of the filtering mass scale in the presence of magnetic fields. This tends to decrease the 21 cm signal compared to the zero-field case. In summary, we find that 21 cm observations may become a promising tool to constrain primordial magnetic fields.
Safety of high speed guided ground transportation systems: Comparison of magnetic and electric fields of conventional and advanced electrified transportation systems. Final report, September 1992-March 1993
Dietrich, F.M.; Feero, W.E.; Jacobs, W.L.
Concerns exist regarding the potential safety, environmental and health effects on the public and on transportation workers due to electrification along new or existing rail corridors, and to proposed maglev and high speed rail operations. Therefore, the characterization of electric and magnetic fields (EMF) produced by both steady (dc) and alternating currents (ac) at power frequency (50 Hz in Europe and 60 Hz in the U.S.) and above, in the Extreme Low Frequency (ELF) range (3-3000 Hz) is of interest. The report summarizes and compares the results of a survey of EMF characteristics (spatial, temporal and frequency bands) for representative conventional railroad and transit and advanced high-speed systems including: the German TR-07 maglev system; the Amtrak Northeast Corridor (NEC) and North Jersey Transit (NJT) trains; the Washington, DC Metrorail (WMATA) and the Boston, MA (MBTA) transit systems; and the French TGV-A high speed rail system. This comprehensive comparative EMF survey produced both detailed data and statistical summaries of EMF profiles, and their variability in time and space. EMF ELF levels for WMATA are also compared to those produced by common environmental sources at home, work, and under power lines, but have specific frequency signatures.
Magnetic Fields in Quasar Cores II
G. B. Taylor
Multi-frequency polarimetry with the Very Long Baseline Array (VLBA) telescope has revealed absolute Faraday Rotation Measures (RMs) in excess of 1000 rad/m/m in the central regions of 7 out of 8 strong quasars studied (e.g., 3C 273, 3C 279, 3C 395). Beyond a projected distance of ~20 pc, however, the jets are found to have |RM| < 100 rad/m/m. Such sharp RM gradients cannot be produced by cluster or galactic-scale magnetic fields, but rather must be the result of magnetic fields organized over the central 1-100 pc. The RMs of the sources studied to date and the polarization properties of BL Lacs, quasars and galaxies are shown to be consistent so far with the predictions of unified schemes. The direct detection of high RMs in these quasar cores can explain the low fractional core polarizations usually observed in quasars at centimeter wavelengths as the result of irregularities in the Faraday screen on scales smaller than the telescope beam. Variability in the RM of the core is reported for 3C 279 between observations taken 1.5 years apart, indicating that the Faraday screen changes on that timescale, or that the projected superluminal motion of the inner jet components samples a new location in the screen with time. Either way, these changes in the Faraday screen may explain the dramatic variability in core polarization properties displayed by quasars.
Quantum Vacuum Friction in Highly Magnetized Neutron Stars
Arnaud Dupays; Carlo Rizzo; Dimitar Bakalov; Giovanni F. Bignami
In this letter we calculate the energy loss of highly magnetized neutron star due to friction with quantum vacuum, namely Quantum Vacuum Friction (QVF). Taking into account one-loop corrections in the effective Heisenberg-Euler Lagrangian of the light-light interaction, we derive an analytic expression for QVF allowing us to consider magnetic field at the surface of the star as high as $10^{11} $T. In the case of magnetars with high magnetic field above the QED critical field, we show that the energy loss by QVF dominates the energy loss process. This has important consequences, in particular on the inferred value of the magnetic field. This also indicates the need for independent measurements of magnetic field, energy loss rate, and of the braking index to fully characterize magnetars.
About the global magnetic fields of stars
Bychkov, V D; Madej, J
We present a review of observations of the stellar longitudinal (effective) magnetic field ($B_e$) and its properties. This paper also discusses contemporary views on the origin, evolution and structure of $B_e$.
Lunar magnetic field measurements with a cubesat
Garrick-Bethell, Ian
We have developed a mission concept that uses 3-unit cubesats to perform new measurements of lunar magnetic fields, less than 100 meters above the MoonÆs surface. The mission calls for sending the cubesats on impact ...
Analysis of Biological Effects and Limits of Exposure to Weak Magnetic Fields
Halgamuge, Malka N.
to weak magnetic fields and geomagnetic field to elucidate the main points of contention. Most of the weak excitation and cardio stimulation can be caused due to the current induced in the body from high power fields [2]. The energy absorption rate of these high power magnetic fields is measured by the specific
High strain in polycrystalline Ni{sub 48.8}Mn{sub 31.4}Ga{sub 19.8} Heusler alloys under overlapped static and oscillating magnetic fields
Montanher, D. Z.; Pereira, J. R. D.; C¾tica, L. F.; Santos, I. A. [Department of Physics, State University of Maringß, Av. Colombo 5790, Maringß - PR 87020-900 (Brazil); Gotardo, R. A. M. [Technological Federal University of Paranß, Av. Alberto Carazzai 1640, Cornķlio Proc¾pio - PR 86300-000 (Brazil); Viana, D. S. F.; Garcia, D.; Eiras, J. A. [Department of Physics, Federal University of SŃo Carlos, Rod. Washington Luiz, Km 235, SŃo Carlos - SP 13565-905 (Brazil)
Martensitic polycrystalline Ni{sub 48.8}Mn{sub 31.4}Ga{sub 19.8} Heusler alloys, with a stacking period of 14 atomic planes at room temperature, were innovatively processed by combining high-energy ball milling and powder metallurgy. Bulk samples were mechanically coupled to a piezoelectric material in a parallel configuration, and the mechanical deformation of the studied system due to the twin's variant motion was investigated under overlapped static and oscillating magnetic fields. A reversible and high mechanical deformation is observed when the frequency of the oscillating magnetic field is tuned with the natural vibration frequency of this system. In this condition, a linear deformation as a function of the static magnetic field amplitude occurs in the ▒4 kOe range, and a mechanical deformation of 2% at 10 kOe is observed.
Torsional Oscillations of Relativistic Stars with Dipole Magnetic Fields
H. Sotani; K. D. Kokkotas; N. Stergioulas
We present the formalism and numerical results for torsional oscillations of relativistic stars endowed with a strong dipole magnetic field. We do a systematic search of parameter space by computing torsional mode frequencies for various values of the harmonic index $\\ell$ and for various overtones, using an extended sample of models of compact stars, varying in mass, high-density equation of state and crust model. We show that torsional mode frequencies are sensitive to the crust model if the high-density equation of state is very stiff. In addition, torsional mode frequencies are drastically affected by a dipole magnetic field, if the latter has a strength exceeding roughly $10^{15}$G and we find that the magnetic field effects are sensitive to the adopted crust model. Using our extended numerical results we derive empirical relations for the effect of the magnetic field on torsional modes as well as for the crust thickness. We compare our numerical results to observed frequencies in SGRs and find that certain high-density EoS and mass values are favored over others in the non-magnetized limit. On the other hand, if the magnetic field is strong, then its effect has to be taken into account in attempts to formulate a theory of asteroseismology for magnetars.
Magnetic field imaging with atomic Rb vapor
Eugeniy E. Mikhailov; I. Novikova; M. D. Havey; F. A. Narducci
We demonstrate the possibility of dynamic imaging of magnetic fields using electromagnetically induced transparency in an atomic gas. As an experimental demonstration we employ an atomic Rb gas confined in a glass cell to image the transverse magnetic field created by a long straight wire. In this arrangement, which clearly reveals the essential effect, the field of view is about 2 x 2 mm^2 and the field detection uncertainty is 0.14 mG per 10 um x 10 um image pixel.
Laminated magnet field coil sheath
Skaritka, J.R.
A method for manufacturing a magnetic cable trim coil in a sheath assembly for use in a cryogenic particle accelerator. A precisely positioned pattern of trim coil turns is bonded to a flexible substrate sheath that is capable of withstanding cryogenic operating conditions. In the method of the invention the flexible substrate sheath, with the trim coil pattern precisely location relative to a bore tube assembly of an accelerator and is then bonded to the bore tube with a tape suitable for cryogenic application. The resultant assembly can be readily handled and installed within an iron magnet yoke assembly of a suitable cryogenic particle accelerator. 1 fig.
Laminated magnet field coil sheath
Skaritka, John R. (Coram, NY)
a method for manufacturing a magnet cable trim coil in a sheath assembly for use in a cryogenic particle accelerator. A precisely positioned pattern of trim coil turns is bonded to a flexible substrate sheath that is capable of withstanding cryogenic operating conditions. In the method of the invention the flexible sheath, with the trim coil pattern precisely positioned thereon, is accurately positioned at a precise location relative to a bore tube assembly of an accelerator and is then bonded to the bore tube with a tape suitable for cryogenic application. The resultant assembly can be readily handled and installed within an iron magnet yoke assembly of a suitable cryogenic particle accelerator.
The influence of the magnetic field on the performance of an active magnetic regenerator (AMR)
Bj°rk, R
The influence of the time variation of the magnetic field, termed the magnetic field profile, on the performance of a magnetocaloric refrigeration device using the active magnetic regeneration (AMR) cycle is studied for a number of process parameters for both a parallel plate and packed bed regenerator using a numerical model. The cooling curve of the AMR is shown to be almost linear far from the Curie temperature of the magnetocaloric material. It is shown that a magnetic field profile that is 10% of the cycle time out of sync with the flow profile leads to a drop in both the maximum temperature span and the maximum cooling capacity of 20-40\\% for both parallel plate and packed bed regenerators. The maximum cooling capacity is shown to depend very weakly on the ramp rate of the magnetic field. Reducing the temporal width of the high field portion of the magnetic field profile by 10% leads to a drop in maximum temperature span and maximum cooling capacity of 5-20%. An increase of the magnetic field from 1 T t...
Error field and magnetic diagnostic modeling for W7-X
Lazerson, Sam A. [PPPL; Gates, David A. [PPPL; NEILSON, GEORGE H. [PPPL; OTTE, M.; Bozhenkov, S.; Pedersen, T. S.; GEIGER, J.; LORE, J.
The prediction, detection, and compensation of error fields for the W7-X device will play a key role in achieving a high beta (? = 5%), steady state (30 minute pulse) operating regime utilizing the island divertor system [1]. Additionally, detection and control of the equilibrium magnetic structure in the scrape-off layer will be necessary in the long-pulse campaign as bootstrapcurrent evolution may result in poor edge magnetic structure [2]. An SVD analysis of the magnetic diagnostics set indicates an ability to measure the toroidal current and stored energy, while profile variations go undetected in the magnetic diagnostics. An additional set of magnetic diagnostics is proposed which improves the ability to constrain the equilibrium current and pressure profiles. However, even with the ability to accurately measure equilibrium parameters, the presence of error fields can modify both the plasma response and diverter magnetic field structures in unfavorable ways. Vacuum flux surface mapping experiments allow for direct measurement of these modifications to magnetic structure. The ability to conduct such an experiment is a unique feature of stellarators. The trim coils may then be used to forward model the effect of an applied n = 1 error field. This allows the determination of lower limits for the detection of error field amplitude and phase using flux surface mapping. *Research supported by the U.S. DOE under Contract No. DE-AC02-09CH11466 with Princeton University.
Particle decay in Ising field theory with magnetic field
Gesualdo Delfino
The scaling limit of the two-dimensional Ising model in the plane of temperature and magnetic field defines a field theory which provides the simplest illustration of non-trivial phenomena such as spontaneous symmetry breaking and confinement. Here we discuss how Ising field theory also gives the simplest model for particle decay. The decay widths computed in this theory provide the obvious test ground for the numerical methods designed to study unstable particles in quantum field theories discretized on a lattice.
Plasma heating in a variable magnetic field
Kichigin, G. N., E-mail: firstname.lastname@example.com [Russian Academy of Sciences, Institute of Solar-Terrestrial Physics (Russian Federation)
The problem of particle acceleration in a periodically variable magnetic field that either takes a zero value or passes through zero is considered. It is shown that, each time the field [0]passes through zero, the particle energy increases abruptly. This process can be regarded as heating in the course of which plasma particles acquire significant energy within one field period. This mechanism of plasma heating takes place in the absence of collisions between plasma particles and is analogous to the mechanism of magnetic pumping in collisional plasma considered by Alfven.
Hyperon bulk viscosity in strong magnetic fields
Monika Sinha; Debades Bandyopadhyay
We study the bulk viscosity of neutron star matter including $\\Lambda$ hyperons in the presence of quantizing magnetic fields. Relaxation time and bulk viscosity due to both the non-leptonic weak process involving $\\Lambda$ hyperons and direct Urca processes are calculated here. In the presence of a strong magnetic field of $10^{17}$ G, the hyperon bulk viscosity coefficient is reduced whereas bulk viscosity coefficients due to direct Urca processes are enhanced compared with their field free cases when many Landau levels are populated by protons, electrons and muons.
Discovery of magnetic fields in hot subdwarfs
S. J. O'Toole; S. Jordan; S. Friedrich; U. Heber
We present initial results of a project to measure mean longitudinal magnetic fields in a group of sdB/OB/O stars. The project was inspired by the discovery of three super-metal-rich sdOB stars, each having metals (e.g. Ti, V) enhanced by factors of 10^3 to 10^5. Similar behaviour is observed in chemically peculiar A stars, where strong magnetic fields are responsible for the enrichment. With this in mind, we obtained circularly polarised spectra of two of the super-metal-rich sdOBs, two "normal" sdBs and two sdOs using FORS1 on the ESO/VLT. By examining circular polarisation in the hydrogen Balmer lines and in helium lines, we have detected magnetic fields with strengths of 1-2 kG in most of our targets. This suggests that such fields are relatively common in hot subdwarfs.
Dynamics of molecular superrotors in external magnetic field
Korobenko, Aleksey
We excite diatomic oxygen and nitrogen to high rotational states with an optical centrifuge and study their dynamics in external magnetic field. Ion imaging is employed to directly visualize, and follow in time, the rotation plane of molecular superrotors. The two different mechanisms of interaction between the magnetic field and the molecular angular momentum in paramagnetic oxygen and non-magnetic nitrogen lead to the qualitatively different behaviour. In nitrogen, we observe the precession of the molecular angular momentum around the field vector. In oxygen, strong spin-rotation coupling results in faster and richer dynamics, encompassing the splitting of the rotation plane in three separate components. As the centrifuged molecules evolve with no significant dispersion of the molecular wave function, the observed magnetic interaction presents an efficient mechanism for controlling the plane of molecular rotation.
Computing nonlinear force free coronal magnetic fields
T. Wiegelmann; T. Neukirch
Knowledge of the structure of the coronal magnetic field is important for our understanding of many solar activity phenomena, e.g. flares and CMEs. However, the direct measurement of coronal magnetic fields is not possible with present methods, and therefore the coronal field has to be extrapolated from photospheric measurements. Due to the low plasma beta the coronal magnetic field can usually be assumed to be approximately force free, with electric currents flowing along the magnetic field lines. There are both observational and theoretical reasons which suggest that at least prior to an eruption the coronal magnetic field is in a nonlinear force free state. Unfortunately the computation of nonlinear force free fields is way more difficult than potential or linear force free fields and analytic solutions are not generally available. We discuss several methods which have been proposed to compute nonlinear force free fields and focus particularly on an optimization method which has been suggested recently. We compare the numerical performance of a newly developed numerical code based on the optimization method with the performance of another code based on an MHD relaxation method if both codes are applied to the reconstruction of a semi-analytic nonlinear force-free solution. The optimization method has also been tested for cases where we add random noise to the perfect boundary conditions of the analytic solution, in this way mimicking the more realistic case where the boundary conditions are given by vector magnetogram data. We find that the convergence properties of the optimization method are affected by adding noise to the boundary data and we discuss possibilities to overcome this difficulty.
Tevzadze, Alexander G. [Faculty of Exact and Natural Sciences, Javakhishvili Tbilisi State University, 1 Chavchavadze Avenue, Tbilisi 0128 (Georgia); Kisslinger, Leonard; Kahniashvili, Tina [McWilliams Center for Cosmology and Department of Physics, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA 15213 (United States); Brandenburg, Axel, E-mail: email@example.com [Nordita, KTH Royal Institute of Technology and Stockholm University, Roslagstullsbacken 23, SE-10691 Stockholm (Sweden)
We study the evolution of QCD phase transition-generated magnetic fields (MFs) in freely decaying MHD turbulence of the expanding universe. We consider an MF generation model that starts from basic non-perturbative QCD theory and predicts stochastic MFs with an amplitude of the order of 0.02 {mu}G and small magnetic helicity. We employ direct numerical simulations to model the MHD turbulence decay and identify two different regimes: a 'weakly helical' turbulence regime, when magnetic helicity increases during decay, and 'fully helical' turbulence, when maximal magnetic helicity is reached and an inverse cascade develops. The results of our analysis show that in the most optimistic scenario the magnetic correlation length in the comoving frame can reach 10 kpc with the amplitude of the effective MF being 0.007 nG. We demonstrate that the considered model of magnetogenesis can provide the seed MF for galaxies and clusters.
Studies of Nb3Sn Strands Based on the Restacked-Rod Process for High-Field Accelerator Magnets Nb3Sn
Barzi, E; Bossert, M; Gallo, G; Lombardo, V; Turrioni, D; Yamada, R; Zlobin, A V
A major thrust in Fermilab's accelerator magnet R&D program is the development of Nb3Sn wires which meet target requirements for high field magnets, such as high critical current density, low effective filament size, and the capability to withstand the cabling process. The performance of a number of strands with 150/169 restack design produced by Oxford Superconducting Technology was studied for round and deformed wires. To optimize the maximum plastic strain, finite element modeling was also used as an aid in the design. Results of mechanical, transport and metallographic analyses are presented for round and deformed wires.
Baldner, Charles S.; Basu, Sarbani [Department of Astronomy, Yale University, P.O. Box 208101, New Haven, CT, 06520-8101 (United States); Antia, H. M. [Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400005 (India); Larson, Timothy P., E-mail: firstname.lastname@example.com [Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA 94305-4085 (United States)
Normal modes of oscillation of the Sun are useful probes of the solar interior. In this work, we use the even-order splitting coefficients to study the evolution of magnetic fields in the convection zone over solar cycle 23, assuming that the frequency splitting is only due to rotation and a large-scale magnetic field. We find that the data are best fit by a combination of a poloidal field and a double-peaked near-surface toroidal field. The toroidal fields are centered at r {sub 0} = 0.999 R {sub sun} and r = 0.996 R {sub sun} and are confined to the near-surface layers. The poloidal field is a dipole field. The peak strength of the poloidal field is 124 +- 17 G. The toroidal field peaks at 380 +- 30 G and 1.4 +- 0.2 kG for the shallower and deeper fields, respectively. The field strengths are highly correlated with surface activity. The toroidal field strength shows a hysteresis-like effect when compared to the global 10.7 cm radio flux. The poloidal field strength shows evidence of saturation at high activity.
Spectroscopic Determination of the Magnetic Fields in Exploding Wire and X-pinch Plasmas
Hammer, David A.
In this report, we summarize the progress that was made toward developing a new magnetic field diagnostic known as Zeeman Broadening for current carrying high energy density plasmas.
Current induced perpendicular-magnetic-anisotropy racetrack memory with magnetic field assistance
Zhang, Y.; Klein, J.-O.; Chappert, C.; Ravelosona, D. [IEF, University of Paris-Sud, Orsay 91405 (France); UMR8622, CNRS, Orsay 91405 (France); Zhao, W. S., E-mail: firstname.lastname@example.com [IEF, University of Paris-Sud, Orsay 91405 (France); UMR8622, CNRS, Orsay 91405 (France); Electronics and Information Engineering School, University of Beihang, Beijing 100191 (China)
High current density is indispensable to shift domain walls (DWs) in magnetic nanowires, which limits the using of racetrack memory (RM) for low power and high density purposes. In this paper, we present perpendicular-magnetic-anisotropy (PMA) Co/Ni RM with global magnetic field assistance, which lowers the current density for DW motion. By using a compact model of PMA RM and 40?nm design kit, we perform mixed simulation to validate the functionality of this structure and analyze its density potential. Stochastic DW motion behavior has been taken into account and statistical Monte-Carlo simulations are carried out to evaluate its reliability performance.
Magnetic Fields of Uranus and Neptune: Metallic Fluid Hydrogen
Nellis, W J
The magnetic fields of the Ice Giant Planets Uranus and Neptune (U/N) are unique in the solar system. Based on a substantial database measured on Earth for representative planetary fluids at representative dynamic pressures up to 200 GPa (2 Mbar) and a few 1000 K, the complex magnetic fields of U/N are (i) probably made primarily by degenerate metallic fluid H (MFH) at or near the crossover from the H-He envelopes to Ice cores at ~100 GPa (Mbar) pressures and normalized radii of ~90% of the radii of U/N; (ii) because those magnetic fields are made relatively close to the surfaces of U/N, non-dipolar fields can be expected; (iii) the Ice cores are most probably a heterogeneous fluid mixture of H, N, O, C, Fe/Ni and silicate-oxides and their mutual reaction products at high pressures and temperatures; (iv) the shapes of the magnetic fields are probably caused by weak coupling between rotational motions of U/N and convective motions of conducting fluids in dynamos that make those magnetic fields. Ironically, the...
Electric-Field Control of Magnetism Intrinsic magnetoelectric coupling describes the microscopic interaction between magnetic and
Maroncelli, Mark
Electric-Field Control of Magnetism Intrinsic magnetoelectric coupling describes the microscopic interaction between magnetic and electric polarization in a single-phase material. The control of the magnetic of the two interactions. Moderate biaxial compression precipitates local magnetic competition
Sensor for detecting changes in magnetic fields
Praeg, W.F.
A sensor is described for detecting changes in the magnetic field of the equilibrium-field coil of a Tokamak plasma device that comprises a pair of bifilar wires disposed circumferentially, one inside and one outside the equilibrium-field coil. Each is shorted at one end. The difference between the voltages detected at the other ends of the bifilar wires provides a measure of changing flux in the equilibrium-field coil. This difference can be used to detect faults in the coil in time to take action to protect the coil.
Sensor for detecting changes in magnetic fields
Praeg, Walter F. (Palos Park, IL)
A sensor for detecting changes in the magnetic field of the equilibrium-field coil of a Tokamak plasma device comprises a pair of bifilar wires disposed circumferentially, one inside and one outside the equilibrium-field coil. Each is shorted at one end. The difference between the voltages detected at the other ends of the bifilar wires provides a measure of changing flux in the equilibrium-field coil. This difference can be used to detect faults in the coil in time to take action to protect the coil.
High Temperature, Permanent Magnet Biased Magnetic Bearings
Gandhi, Varun R.
, then the molding process was carried out to form the potting cement on the each stator. After this the stators are baked in the oven and once ready the magnets and back-irons are put onto the stator. Shown below in Figure 3-11 is an assembly tool designed... rings. The bearing and its support rings were then carried onto the test rig and mounted at one end of the table. Throughout the assembly process a lot of care had to be taken so as to avoid damaging of the permanent magnets, stator and its coils...
Fast field mapping device for cyclotron magnets
Berkes, B.; Brombach, D.; Szavits, O.
The Swiss S.I.N. ring injector cyclotron has four sector magnets. For fast and accurate magnetic field measurements a new type of measuring system has been developed. The magnetic field of the sector magnets is measured in polar coordinates. The standard field map covers a range in radial direction from 240 to 3800 mm and in azimuthal direction from -47 deg. to +47 deg. in steps of 20 mm and 1/4 deg., respectively. Two Hall probes are mounted on a carriage which follows a meandric track. The data are taken in the ''flying'' mode, i.e. two fast DVM's read the values while the carriage is moving at an average speed of approx. 25 cm/sec. The measuring procedure is controlled on line by a small computer and is carried through automatically within roughly 2/one-half/ hr. The process control software contains diagnostic routines for surveying the operation as well as for a smoothing check of the measured data which are written on a magnetic tape at the end of each radial track. 3 refs.
Constraining Cosmic Magnetic Fields by a Measurement of
Erdmann, Martin
. . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 7 Energy-Energy-Correlations 51 7.1 Definition of Energy-EnergyConstraining Cosmic Magnetic Fields by a Measurement of Energy-Energy-Correlations with the Pierre Ultra High Energy Cosmic Rays 3 2.1 Cosmic Rays with Energies below 4 Ee
Magnetic fields and density functional theory
Salsbury Jr., Freddie
A major focus of this dissertation is the development of functionals for the magnetic susceptibility and the chemical shielding within the context of magnetic field density functional theory (BDFT). These functionals depend on the electron density in the absence of the field, which is unlike any other treatment of these responses. There have been several advances made within this theory. The first of which is the development of local density functionals for chemical shieldings and magnetic susceptibilities. There are the first such functionals ever proposed. These parameters have been studied by constructing functionals for the current density and then using the Biot-Savart equations to obtain the responses. In order to examine the advantages and disadvantages of the local functionals, they were tested numerically on some small molecules.
Magnetic field-line lengths inside interplanetary magnetic flux ropes
Hu, Qiang; Krucker, Sam
We report on the detailed and systematic study of field-line twist and length distributions within magnetic flux ropes embedded in Interplanetary Coronal Mass Ejections (ICMEs). The Grad-Shafranov reconstruction method is utilized together with a constant-twist nonlinear force-free (Gold-Hoyle) flux rope model to reveal the close relation between the field-line twist and length in cylindrical flux ropes, based on in-situ Wind spacecraft measurements. We show that the field-line twist distributions within interplanetary flux ropes are inconsistent with the Lundquist model. In particular we utilize the unique measurements of magnetic field-line lengths within selected ICME events as provided by Kahler et al. (2011) based on energetic electron burst observations at 1 AU and the associated type III radio emissions detected by the Wind spacecraft. These direct measurements are compared with our model calculations to help assess the flux-rope interpretation of the embedded magnetic structures. By using the differen...
Modeling spin magnetization transport in a spatially varying magnetic field
Rico A. R. Picone; Joseph L. Garbini; John A. Sidles
We present a framework for modeling the transport of any number of globally conserved quantities in any spatial configuration and apply it to obtain a model of magnetization transport for spin-systems that is valid in new regimes (including high-polarization). The framework allows an entropy function to define a model that explicitly respects the laws of thermodynamics. Three facets of the model are explored. First, it is expressed as nonlinear partial differential equations that are valid for the new regime of high dipole-energy and polarization. Second, the nonlinear model is explored in the limit of low dipole-energy (semi-linear), from which is derived a physical parameter characterizing separative magnetization transport (SMT). It is shown that the necessary and sufficient condition for SMT to occur is that the parameter is spatially inhomogeneous. Third, the high spin-temperature (linear) limit is shown to be equivalent to the model of nuclear spin transport of Genack and Redfield. Differences among the three forms of the model are illustrated by numerical solution with parameters corresponding to a magnetic resonance force microscopy (MRFM) experiment. A family of analytic, steady-state solutions to the nonlinear equation is derived and shown to be the spin-temperature analog of the Langevin paramagnetic equation and Curie's law. Finally, we analyze the separative quality of magnetization transport, and a steady-state solution for the magnetization is shown to be compatible with Fenske's separative mass transport equation.
Circular polarization of obliquely propagating whistler wave magnetic field
Bellan, P. M. [Applied Physics, Caltech, Pasadena California 91125 (United States)] [Applied Physics, Caltech, Pasadena California 91125 (United States)
The circular polarization of the magnetic field of obliquely propagating whistler waves is derived using a basis set associated with the wave partial differential equation. The wave energy is mainly magnetic and the wave propagation consists of this magnetic energy sloshing back and forth between two orthogonal components of magnetic field in quadrature. The wave electric field energy is small compared to the magnetic field energy.
Magnetic fields of the W4 superbubble
Gao, X Y; Reich, P; Han, J L; Kothes, R
Superbubbles and supershells are the channels for transferring mass and energy from the Galactic disk to the halo. Magnetic fields are believed to play a vital role in their evolution. We study the radio continuum and polarized emission properties of the W4 superbubble to determine its magnetic field strength. New sensitive radio continuum observations were made at 6 cm, 11 cm, and 21 cm. The total intensity measurements were used to derive the radio spectrum of the W4 superbubble. The linear polarization data were analysed to determine the magnetic field properties within the bubble shells. The observations show a multi-shell structure of the W4 superbubble. A flat radio continuum spectrum that stems from optically thin thermal emission is derived from 1.4 GHz to 4.8 GHz. By fitting a passive Faraday screen model and considering the filling factor fne , we obtain the thermal electron density ne = 1.0/\\sqrt{fne} (\\pm5%) cm^-3 and the strength of the line-of-sight component of the magnetic field B// = -5.0/\\sq...
Measurement of Magnetic Field Using Collaborative AUVs
Idaho, University of
Measurement of Magnetic Field Using Collaborative AUVs Jesse Pentzer, Brendan Crosbie, Thomas Bean, tests using multiple types of AUVs to individually sample bathymetric data and water mass properties, salinity, and temperature data was reported [2]. In 2007, an AUV was equipped to measure water properties
Electrostatic waves in carbon nanotubes with an axial magnetic field
Abdikian, Alireza [Department of Physics, Malayer University, Malayer 65719-95863 (Iran, Islamic Republic of)] [Department of Physics, Malayer University, Malayer 65719-95863 (Iran, Islamic Republic of); Bagheri, Mehran [Laser and Plasma Research Institute, Shahid Beheshti University, G. C., Evin, Tehran 19835-63113 (Iran, Islamic Republic of)] [Laser and Plasma Research Institute, Shahid Beheshti University, G. C., Evin, Tehran 19835-63113 (Iran, Islamic Republic of)
Based on a linearized hydrodynamic model and within the quasi-static approximation, the dispersion relation of electrostatic waves propagating through single-walled carbon nanotubes subject to an axial magnetic field is theoretically explored. In the classical limit, we obtain two main possible waves which in turn are divided into two branches, a low-frequency acoustical and a high-frequency optical plasmon branch. In the quantum case, we have found that the dispersion relation is substantially modified when the electron wavelength becomes large enough compared to the propagation wavelength of the electrostatic waves in the quantum plasma. We also show that the axial magnetic field manifest itself on the perturbed electron density through the quantum term and gives rise to the propagation of the electrostatic waves within the quantum plasma. As a result, the effect of the magnetic field is pronounced in the plasma dispersion relations in such a way that their curves approach to zero when the magnetic field is weak; and for the strong magnetic field, they asymptotically meet the constant lines.
System Identification and Signal Processing for PID Control of B0 Shim Systems in Ultra-High Field Magnetic Resonance Applications
System Identification and Signal Processing for PID Control of B0 Shim Systems in Ultra-High Field identification; parameter optimization; smoothing filters; phase-locked loop; Hurwitz criterion; PID controllers
Polarizable vacuum analysis of electric and magnetic fields
Xing-Hao Ye
The electric and magnetic fields are investigated on the basis of quantum vacuum. The analysis of the electromagnetic energy and force indicates that an electric field is a polarized distribution of the vacuum virtual dipoles, and that a magnetic field in vacuum is a rearrangement of the vacuum polarization. It means that an electromagnetic wave is a successional changing of the vacuum polarization in space. Also, it is found that the average half length of the virtual dipoles around an elementary charge is a=2.8 *10^(-15)m. The result leads to the step distribution of the field energy around an electron, the relation between the fine structure constant and the vacuum polarization distribution, and an extremely high energy density of the electromagnetic field.
Massive disk outflows mediated by extreme magnetic fields
Shiber, Sagiv; Soker, Noam
We argue that magnetic fields amplified within a very high accretion-rate disk around main sequence stars can lead to the formation of massive bipolar outflows that can remove most of the disk's mass and energy. This efficient directional removal of energy and mass allows the high accretion-rate disk to be built. We construct thick disks where the magnetic fields are amplified by an Alpha-Omega dynamo in the disk, bringing the fluctuating components of the magnetic field to be much stronger than the large-scale component. By examining the possible activity of the magnetic fields we conclude that main sequence stars can accrete mass at very high rates, up to 0.01Mo/yr for solar type stars, and up to 1Mo/yr for very massive stars. Such energetic outflows can account for the powering of some eruptive objects, such as merging main sequence stars, major eruptions of luminous blue variables, such as the Great Eruption of Eta Carinae, and other intermediate luminosity optical transients (ILOTs; Red Novae; Red Transi...
Magnetic Fields in Molecular Cloud Cores
Shantanu Basu
Observations of magnetic field strengths imply that molecular cloud fragments are individually close to being in a magnetically critical state, even though both magnetic field and column density measurements range over two orders of magnitude. The turbulent pressure also approximately balances the self-gravitational pressure. These results together mean that the one-dimensional velocity dispersion $\\sigv$ is proportional to the mean \\Alf speed of a cloud $\\va$. Global models of MHD turbulence in a molecular cloud show that this correlation is naturally satisfied for a range of different driving strengths of the turbulence. For example, an increase of turbulent driving causes a cloud expansion which also increases $\\va$. Clouds are in a time averaged balance but exhibit large oscillatory motions, particularly in their outer rarefied regions. We also discuss models of gravitational fragmentation in a sheet-like region in which turbulence has already dissipated, including the effects of magnetic fields and ion-neutral friction. Clouds with near-critical mass-to-flux ratios lead to subsonic infall within cores, consistent with some recent observations of motions in starless cores. Conversely, significantly supercritical clouds are expected to produce extended supersonic infall.
The measurement and analysis of the magnetic field of a synchrotron light source magnetĀ
Graf, Udo Werner
In this thesis a unique system is used to measure the magnetic field of a superconducting synchrotron light source magnet. The magnet measured is a superferric dipole C-magnet designed to produce a magnetic field up to 3 Tesla in magnitude. Its...
Primordial magnetic field amplification from turbulent reheating
Calzetta, Esteban [Departamento de FĒsica, FCEyN-UBA and IFIBA-CONICET, Cdad. Universitaria, Buenos Aires (Argentina); Kandus, Alejandra, E-mail: email@example.com, E-mail: firstname.lastname@example.com [LATO - DCET - UESC. Rodovia Ilhķus-Itabuna, km 16 s/n, CEP: 45662-900, Salobrinho, Ilhķus-BA (Brazil)
We analyze the possibility of primordial magnetic field amplification by a stochastic large scale kinematic dynamo during reheating. We consider a charged scalar field minimally coupled to gravity. During inflation this field is assumed to be in its vacuum state. At the transition to reheating the state of the field changes to a many particle/anti-particle state. We characterize that state as a fluid flow of zero mean velocity but with a stochastic velocity field. We compute the scale-dependent Reynolds number Re(k), and the characteristic times for decay of turbulence, t{sub d} and pair annihilation t{sub a}, finding t{sub a} << t{sub d}. We calculate the rms value of the kinetic helicity of the flow over a scale L and show that it does not vanish. We use this result to estimate the amplification factor of a seed field from the stochastic kinematic dynamo equations. Although this effect is weak, it shows that the evolution of the cosmic magnetic field from reheating to galaxy formation may well be more complex than as dictated by simple flux freezing.
Investigation of Mechanical Activation on Li-N-H Systems Using 6Li Magic Angle Spinning Nuclear Magnetic Resonance at Ultra-High Field
Hu, Jian Zhi; Kwak, Ja Hun; Yang, Zhenguo; Osborn, William; Markmaitree, Tippawan; Shaw, Leonard D.
Abstract The significantly enhanced spectral resolution in the 6Li MAS NMR spectra of Li-N-H systems at ultra-high field of 21.1 tesla is exploited, for the first time, to study the detailed electronic and chemical environmental changes associated with mechanical activation of Li-N-H system using high energy balling milling. Complementary to ultra-high field studies, the hydrogen discharge dynamics are investigated using variable temperature in situ 1H MAS NMR at 7.05 tesla field. The significantly enhanced spectral resolution using ultra-high filed of 21.1 tesla was demonstrated along with several major findings related to mechanical activation, including the upfield shift of the resonances in 6Li MAS spectra induced by ball milling, more efficient mechanical activation with ball milling at liquid nitrogen temperature than with ball milling at room temperature, and greatly enhanced hydrogen discharge exhibited by the liquid nitrogen ball milled samples.
Magnetic susceptibility and magnetization properties of asymmetric nuclear matter under a strong magnetic field
A. Rabhi; M. A. Pķrez-GarcĒa; C. ProvidĻncia; I. Vida±a
We study the effect of a strong magnetic field on the proton and neutron spin polarization and magnetic susceptibility of asymmetric nuclear matter within a relativistic mean-field approach. It is shown that magnetic fields $B \\sim 10^{16} - 10^{17}$ G have already noticeable effects on the range of densities of interest for the study of the crust of a neutron star. Although the proton susceptibility is larger for weaker fields, the neutron susceptibility becomes of the same order or even larger for small proton fractions and subsaturation densities for $B > 10^{16}$ G. We expect that neutron superfluidity in the crust will be affected by the presence of magnetic fields.
Magnetic Fields in Population III Star Formation
Turk, Matthew J.; Oishi, Jeffrey S.; Abel, Tom; Bryan, Greg
We study the buildup of magnetic fields during the formation of Population III star-forming regions, by conducting cosmological simulations from realistic initial conditions and varying the Jeans resolution. To investigate this in detail, we start simulations from identical initial conditions, mandating 16, 32 and 64 zones per Jeans length, and studied the variation in their magnetic field amplification. We find that, while compression results in some amplification, turbulent velocity fluctuations driven by the collapse can further amplify an initially weak seed field via dynamo action, provided there is sufficient numerical resolution to capture vortical motions (we find this requirement to be 64 zones per Jeans length, slightly larger than, but consistent with previous work run with more idealized collapse scenarios). We explore saturation of amplification of the magnetic field, which could potentially become dynamically important in subsequent, fully-resolved calculations. We have also identified a relatively surprising phenomena that is purely hydrodynamic: the higher-resolved simulations possess substantially different characteristics, including higher infall-velocity, increased temperatures inside 1000 AU, and decreased molecular hydrogen content in the innermost region. Furthermore, we find that disk formation is suppressed in higher-resolution calculations, at least at the times that we can follow the calculation. We discuss the effect this may have on the buildup of disks over the accretion history of the first clump to form as well as the potential for gravitational instabilities to develop and induce fragmentation.
Proton radiography of magnetic field produced by ultra-intense laser irradiating capacity-coil target
Wang, W W; Chen, J; Cai, H B; He, S K; Zhou, W M; Shan, L Q; Lu, F; Wu, Y C; Hong, W; Liu, D X; Bi, B; Zhang, F; Xue, F B; Li, B Y; Zhang, B; He, Y L; He, W; Jiao, J L; Dong, K G; Zhang, F Q; Deng, Z G; Zhang, Z M; Cui, B; Han, D; Zhou, K N; Wang, X D; Zhao, Z Q; Cao, L F; Zhang, B H; He, X T; Gu, Y Q
Ultra-intense ultra-short laser is firstly used to irradiate the capacity-coil target to generate magnetic field. The spatial structure and temporal evolution of huge magnetic fields were studied with time-gated proton radiography method. A magnetic flux density of 40T was measured by comparing the proton deflection and particle track simulations. Although the laser pulse duration is only 30fs, the generated magnetic field can last for over 100 picoseconds. The energy conversion efficiency from laser to magnetic field can reach as high as ~20%. The results indicate that tens of tesla (T) magnetic field could be produced in many ultra intense laser facilities around the world, and higher magnetic field could be produced by picosecond lasers.
Control of stochasticity in magnetic field lines
Cristel Chandre; Michel Vittot; Guido Ciraolo; Philippe Ghendrih; Ricardo Lima
We present a method of control which is able to create barriers to magnetic field line diffusion by a small modification of the magnetic perturbation. This method of control is based on a localized control of chaos in Hamiltonian systems. The aim is to modify the perturbation locally by a small control term which creates invariant tori acting as barriers to diffusion for Hamiltonian systems with two degrees of freedom. The location of the invariant torus is enforced in the vicinity of the chosen target. Given the importance of confinement in magnetic fusion devices, the method is applied to two examples with a loss of magnetic confinement. In the case of locked tearing modes, an invariant torus can be restored that aims at showing the current quench and therefore the generation of runaway electrons. In the second case, the method is applied to the control of stochastic boundaries allowing one to define a transport barrier within the stochastic boundary and therefore to monitor the volume of closed field lines.
Accretion Discs with Strong Toroidal Magnetic Fields
M. C. Begelman; J. E. Pringle
Simulations and analytic arguments suggest that the turbulence driven by magnetorotational instability (MRI) in accretion discs can amplify the toroidal (azimuthal) component of the magnetic field to a point at which magnetic pressure exceeds the combined gas + radiation pressure in the disc. Arguing from the recent analysis by Pessah and Psaltis, and other MRI results in the literature, we conjecture that the limiting field strength for a thin disc is such that the Alfven speed roughly equals the geometric mean of the Keplerian speed and the gas sound speed. We examine the properties of such magnetically-dominated discs, and show that they resolve a number of outstanding problems in accretion disc theory. The discs would be thicker than standard (Shakura-Sunyaev) discs at the same radius and accretion rate, and would tend to have higher colour temperatures. If they transport angular momentum according to an alpha-prescription, they would be stable against the thermal and viscous instabilities that are found in standard disc models. In discs fuelling active galactic nuclei, magnetic pressure support could also alleviate the restriction on accretion rate imposed by disc self-gravity.
Spin Chain in Magnetic Field: Limitations of the Large-N Mean-Field Theory
DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)
Wohlfeld, K.; Chen, Cheng-Chien; van Veenendaal, M.; Devereaux, T.P.
Motivated by the recent success in describing the spin and orbital spectrum of a spin-orbital chain using a large-N mean-field approximation [Phys. Rev. B 91, 165102 (2015)], we apply the same formalism to the case of a spin chain in the external magnetic field. It occurs that in this case, which corresponds to N=2 in the approximation, the large-N mean-field theory cannot qualitatively reproduce the spin excitation spectra at high magnetic fields, which polarize more than 50% of the spins in the magnetic ground state. This, rather counterintuitively, shows that the physics of a spin chain can under some circumstancesmoreĀ╗be regarded as more complex than the physics of a spin-orbital chain.½Āless
Solar magnetic fields and terrestrial climate
Georgieva, Katya; Kirov, Boian
Solar irradiance is considered one of the main natural factors affecting terrestrial climate, and its variations are included in most numerical models estimating the effects of natural versus anthropogenic factors for climate change. Solar wind causing geomagnetic disturbances is another solar activity agent whose role in climate change is not yet fully estimated but is a subject of intense research. For the purposes of climate modeling, it is essential to evaluate both the past and the future variations of solar irradiance and geomagnetic activity which are ultimately due to the variations of solar magnetic fields. Direct measurements of solar magnetic fields are available for a limited period, but can be reconstructed from geomagnetic activity records. Here we present a reconstruction of total solar irradiance based on geomagnetic data, and a forecast of the future irradiance and geomagnetic activity relevant for the expected climate change.
Ferrofluid aggregates phase transitions in the planar magnetic field
V. F. Kovalenko; M. V. Petrychuk; B. M. Tanygin; S. I. Shulyma
The influence of the cyclic heating and cooling on properties of the aggregates (aka "ferrofluid clusters") in a ferrofluid, which made on the basis of magnetite nanoparticles, are investigated. The heating of the ferrofluid layer with such aggregates leads to equalization of the concentration between high- and low-concentrated phases. The temperature of the equalization of the phase concentrations was determined at different values of an external constant magnetic field, which was applied parallel to the layer of the ferrofluid. The temperature of the destruction of a periodic structure of the magnetic aggregates, which were formed during cooling of a homogeneous phase of the ferrofluid, was obtained at the different values of the applied external magnetic field.
Fluorescent lamp with static magnetic field generating means
Moskowitz, P.E.; Maya, J.
A fluorescent lamp wherein magnetic field generating means (e.g., permanent magnets) are utilized to generate a static magnetic field across the respective electrode structures of the lamp such that maximum field strength is located at the electrode's filament. An increase in efficacy during operation has been observed. 2 figs.
Localized Magnetic Fields in Arbitrary Directions Using Patterned Nanomagnets
Dunin-Borkowski, Rafal E.
with the option of applying electric fields, for example, to move a quantum dot between regions where the magnetic magnetic films have a long history, for example, in bubble memory,6 but on scales required for spintronic electric fields, for example, to move a quantum dot between regions where the magnetic-field direction
Mapping the magnetic field vector in a fountain clock
Gertsvolf, Marina; Marmet, Louis [National Research Council of Canada, Ottawa, Ontario K1A 0R6 (Canada)
We show how the mapping of the magnetic field vector components can be achieved in a fountain clock by measuring the Larmor transition frequency in atoms that are used as a spatial probe. We control two vector components of the magnetic field and apply audio frequency magnetic pulses to localize and measure the field vector through Zeeman spectroscopy.
Quantitative Modeling of High Temperature Magnetization Dynamics
Zhang, Shufeng
Final Technical Report Project title: Quantitative Modeling of High Temperature Magnetization Dynamics DOE/Office of Science Program Manager Contact: Dr. James Davenport
Heat pulse propagation in chaotic 3-dimensional magnetic fields
D. del-Castillo-Negrete; D. Blazevski
Heat pulse propagation in $3$-D chaotic magnetic fields is studied by solving the parallel heat transport equation using a Lagrangian-Green's function (LG) method. The LG method provides an efficient and accurate technique that circumvents limitations of finite elements and finite difference methods. The main two problems addressed are: (i) The dependence of the radial transport on the magnetic field stochasticity (controlled by the amplitude of the perturbation, $\\epsilon$); and (ii) The role of reversed shear configurations on pulse propagation. In all the cases considered there are no magnetic flux surfaces. However, radial transport is observed to depend strongly on $\\epsilon$ due to the presence of high-order magnetic islands and Cantori that act as quasi-transport barriers that preclude the radial penetration of heat pulses within physically relevant time scale. The dependence of the magnetic field connection length, $\\ell_B$, on $\\epsilon$ is studied in detail. The decay rate of the temperature maximum, $\\langle T \\rangle_{max}(t)$, the time delay of the temperature response as function of the radius, $\\tau$, and the radial heat flux $\\langle {{\\bf q}\\cdot {\\hat e}_\\psi} \\rangle$, are also studied as functions of the magnetic field stochasticity and $\\ell_B$. In all cases, the scaling of $\\langle T \\rangle_{max}$ with $t$ transitions from sub-diffusive, $\\langle T \\rangle_{max} \\sim t^{-1/4}$, at short times ($\\chi_\\parallel t 10^5$). A strong dependence on $\\epsilon$ is also observed on $\\tau$ and $\\langle {{\\bf q}\\cdot {\\hat e}_\\psi} \\rangle$. The radial propagation of pulses in fully chaotic fields considerably slows down in the shear reversal region and, as a result, $\\tau$, in reversed shear configurations is an order of magnitude longer than the one in monotonic $q$-profiles.
Dependence of Brownian and Nķel relaxation times on magnetic field strength
Deissler, Robert J., E-mail: firstname.lastname@example.com; Wu, Yong; Martens, Michael A. [Department of Physics, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, Ohio 44106 (United States)] [Department of Physics, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, Ohio 44106 (United States)
Purpose: In magnetic particle imaging (MPI) and magnetic particle spectroscopy (MPS) the relaxation time of the magnetization in response to externally applied magnetic fields is determined by the Brownian and Nķel relaxation mechanisms. Here the authors investigate the dependence of the relaxation times on the magnetic field strength and the implications for MPI and MPS. Methods: The Fokker¢Planck equation with Brownian relaxation and the Fokker¢Planck equation with Nķel relaxation are solved numerically for a time-varying externally applied magnetic field, including a step-function, a sinusoidally varying, and a linearly ramped magnetic field. For magnetic fields that are applied as a step function, an eigenvalue approach is used to directly calculate both the Brownian and Nķel relaxation times for a range of magnetic field strengths. For Nķel relaxation, the eigenvalue calculations are compared to Brown's high-barrier approximation formula. Results: The relaxation times due to the Brownian or Nķel mechanisms depend on the magnitude of the applied magnetic field. In particular, the Nķel relaxation time is sensitive to the magnetic field strength, and varies by many orders of magnitude for nanoparticle properties and magnetic field strengths relevant for MPI and MPS. Therefore, the well-known zero-field relaxation times underestimate the actual relaxation times and, in particular, can underestimate the Nķel relaxation time by many orders of magnitude. When only Nķel relaxation is presentŚif the particles are embedded in a solid for instanceŚthe authors found that there can be a strong magnetization response to a sinusoidal driving field, even if the period is much less than the zero-field relaxation time. For a ferrofluid in which both Brownian and Nķel relaxation are present, only one relaxation mechanism may dominate depending on the magnetic field strength, the driving frequency (or ramp time), and the phase of the magnetization relative to the applied magnetic field. Conclusions: A simple treatment of Nķel relaxation using the common zero-field relaxation time overestimates the relaxation time of the magnetization in situations relevant for MPI and MPS. For sinusoidally driven (or ramped) systems, whether or not a particular relaxation mechanism dominates or is even relevant depends on the magnetic field strength, the frequency (or ramp time), and the phase of the magnetization relative to the applied magnetic field.
High Field Niobium-Tin Quadrupoles
GianLuca Sabbi
Insertion quadrupoles with large aperture and high gradient are required to achieve the luminosity upgrade goal of 1035 cm-2s-1 at the Large Hadron Collider (LHC). Nb3Sn conductor is required in order to operate at high field and with sufficient temperature margin. We report here on the development of a ōHigh-performance Quadrupoleö (HQ) that will demonstrate the technology required for achieving the target luminosity. Conductor requirements, magnetic, mechanical and quench protection issues are presented and discussed. The HQ design is also suitable for an intermediate ōPhase 1ö upgrade, operating with large engineering margin.
Magnetic fusion energy plasma interactive and high heat flux components. Volume I. Technical assessment of the critical issues and problem areas in the plasma materials interaction field
Conn, R.W.; Gauster, W.B.; Heifetz, D.; Marmar, E.; Wilson, K.L. (eds.)
A technical assessment of the critical issues and problem areas in the field of plasma materials interactions (PMI) in magnetic fusion devices shows these problems to be central for near-term experiments, for intermediate-range reactor devices including D-T burning physics experiments, and for long-term reactor machines. Critical technical issues are ones central to understanding and successful operation of existing and near-term experiments/reactors or devices of great importance for the long run, i.e., ones which will require an extensive, long-term development effort and thus should receive attention now. Four subgroups were formed to assess the critical PMI issues along four major lines: (1) PMI and plasma confinement physics experiments; (2) plasma-edge modelling and theory; (3) surface physics; and (4) materials technology for in-vessel components and the first wall. The report which follows is divided into four major sections, one for each of these topics.
Design and characterization of 2.45 GHz electron cyclotron resonance plasma source with magnetron magnetic field configuration for high flux of hyperthermal neutral beam
Kim, Seong Bong [Department of Physics, Pohang University of Science and Technology, San 31, Hyoja-dong, Nam-gu, Pohang 790-784 (Korea, Republic of); Convergence Plasma Research Center, National Fusion Research Institute, Gwahangno 113, Yuseong-gu, Daejeon 305-333 (Korea, Republic of); Kim, Dae Chul; Yoo, Suk Jae [Convergence Plasma Research Center, National Fusion Research Institute, Gwahangno 113, Yuseong-gu, Daejeon 305-333 (Korea, Republic of); Namkung, Won; Cho, Moohyun [Department of Physics, Pohang University of Science and Technology, San 31, Hyoja-dong, Nam-gu, Pohang 790-784 (Korea, Republic of)
A 2.45 GHz electron cyclotron resonance (ECR) source with a magnetron magnetic field configuration was developed to meet the demand of a hyperthermal neutral beam (HNB) flux on a substrate of more than 1x10{sup 15} cm{sup -2} s{sup -1} for industrial applications. The parameters of the operating pressure, ion density, electron temperature, and distance between the neutralization plate and the substrate for the HNB source are specified in a theoretical analysis. The electron temperature and the ion density are measured to characterize the ECR HNB source using a Langmuir probe and optical emission spectroscopy. The parameters of the ECR HNB source are in good agreement with the theoretically specified parameters.
On the control of solidification using magnetic fields and magnetic field Baskar Ganapathysubramanian and Nicholas Zabaras1
Zabaras, Nicholas J.
On the control of solidification using magnetic fields and magnetic field gradients Baskar and Aerospace Engineering, 188 Frank H.T. Rhodes Hall, Cornell University, Ithaca, NY 14853-3801, USA Abstract solidified material can be suitably affected. Most of the magnetic field approaches to melt flow control rely
We study the interaction of a high frequency AC current with a magnetic field in an YBCO thin film by using time
Shaw, Leah B.
-TC superconductors. The focus of our research is on dynamical processes (electronic, magnetic, and vibrational
Localization of disordered bosons and magnets in random fields
Yu, Xiaoquan, E-mail: firstname.lastname@example.com [International School for Advanced Studies (SISSA), via Bonomea 265, 34136 Trieste (Italy) [International School for Advanced Studies (SISSA), via Bonomea 265, 34136 Trieste (Italy); New Zealand Institute for Advanced Study, Centre for Theoretical Chemistry and Physics, Massey University, Auckland 0745 (New Zealand); M³ller, Markus, E-mail: firstname.lastname@example.com [The Abdus Salam International Center for Theoretical Physics, Strada Costiera 11, 34151 Trieste (Italy)] [The Abdus Salam International Center for Theoretical Physics, Strada Costiera 11, 34151 Trieste (Italy)
We study localization properties of disordered bosons and spins in random fields at zero temperature. We focus on two representatives of different symmetry classes, hard-core bosons (XY magnets) and Ising magnets in random transverse fields, and contrast their physical properties. We describe localization properties using a locator expansion on general lattices. For 1d Ising chains, we find non-analytic behavior of the localization length as a function of energy at ?=0, ?{sup ?1}(?)=?{sup ?1}(0)+A|?|{sup ?}, with ? vanishing at criticality. This contrasts with the much smoother behavior predicted for XY magnets. We use these results to approach the ordering transition on Bethe lattices of large connectivity K, which mimic the limit of high dimensionality. In both models, in the paramagnetic phase with uniform disorder, the localization length is found to have a local maximum at ?=0. For the Ising model, we find activated scaling at the phase transition, in agreement with infinite randomness studies. In the Ising model long range order is found to arise due to a delocalization and condensation initiated at ?=0, without a closing mobility gap. We find that Ising systems establish order on much sparser (fractal) subgraphs than XY models. Possible implications of these results for finite-dimensional systems are discussed. -- Highlights: ĢStudy of localization properties of disordered bosons and spins in random fields. ĢComparison between XY magnets (hard-core bosons) and Ising magnets. ĢAnalysis of the nature of the magnetic transition in strong quenched disorder. ĢIsing magnets: activated scaling, no closing mobility gap at the transition. ĢIsing order emerges on sparser (fractal) support than XY order.
Magnetic helicity generation from the cosmic axion field
Campanelli, L.; Giannotti, M. [Dipartimento di Fisica, Universita di Ferrara, I-44100 Ferrara (Italy); INFN-Sezione di Ferrara, I-44100 Ferrara (Italy)
The coupling between a primordial magnetic field and the cosmic axion field generates a helical component of the magnetic field around the time in which the axion starts to oscillate. If the energy density of the seed magnetic field is comparable to the energy density of the universe at that time, then the resulting magnetic helicity is about vertical bar H{sub B} vertical bar {approx_equal}(10{sup -20}G){sup 2} kpc and remains constant after its generation. As a corollary, we find that the standard properties of the oscillating axion remain unchanged even in the presence of very strong magnetic fields.
Magnetic Helicity Generation from the Cosmic Axion Field
L. Campanelli; M. Giannotti
The coupling between a primordial magnetic field and the cosmic axion field generates a helical component of the magnetic field around the time in which the axion starts to oscillate. If the energy density of the seed magnetic field is comparable to the energy density of the universe at that time, then the resulting magnetic helicity is about |H_B| \\simeq (10^{-20} G)^2 kpc and remains constant after its generation. As a corollary, we find that the standard properties of the oscillating axion remain unchanged even in the presence of very strong magnetic fields.
Magnetic Field Evolution in Superconducting Neutron Stars
Graber, Vanessa; Glampedakis, Kostas; Lander, Samuel K
The presence of superconducting and superfluid components in the core of mature neutron stars calls for the rethinking of a number of key magnetohydrodynamical notions like resistivity, the induction equation, magnetic energy and flux-freezing. Using a multi-fluid magnetohydrodynamics formalism, we investigate how the magnetic field evolution is modified when neutron star matter is composed of superfluid neutrons, type-II superconducting protons and relativistic electrons. As an application of this framework, we derive an induction equation where the resistive coupling originates from the mutual friction between the electrons and the vortex/fluxtube arrays of the neutron and proton condensates. The resulting induction equation allows the identification of two timescales that are significantly different from those of standard magnetohydrodynamics. The astrophysical implications of these results are briefly discussed.
3-Axis Magnetic Sensor Hybrid The Honeywell HMC2003 is a high sensitivity, three-axis magnetic sensor hybrid
Kleinfeld, David
3-Axis Magnetic Sensor Hybrid HMC2003 The Honeywell HMC2003 is a high sensitivity, three-axis magnetic sensor hybrid assembly used to measure low magnetic field strengths. Honeywell's most sensitive Reference, Traffic Detection, Proximity Detection and Medical Devices Honeywell continues to maintain
The origin, evolution and signatures of primordial magnetic fields
Subramanian, Kandaswamy
The universe is magnetized on all scales probed so far. On the largest scales, galaxies and galaxy clusters host magnetic fields at the micro Gauss level coherent on scales up to ten kpc. Recent observational evidence suggests that even the intergalactic medium in voids could host a weak $\\sim 10^{-16}$ Gauss magnetic field, coherent on Mpc scales. An intriguing possibility is that these observed magnetic fields are a relic from the early universe, albeit one which has been subsequently amplified and maintained by a dynamo in collapsed objects. We review here the origin, evolution and signatures of primordial magnetic fields. After a brief summary of magnetohydrodynamics in the expanding universe, we turn to magnetic field generation during inflation and other phase transitions. We trace the linear and nonlinear evolution of the generated primordial fields through the radiation era, including viscous effects. Sensitive observational signatures of primordial magnetic fields on the cosmic microwave background, ...
Adiabatic expansion and magnetic fields in AGN jets
A. B. Pushkarev; Y. Y. Kovalev; A. P. Lobanov
Results of high-resolution simultaneous multi-frequency 8.1-15.4 GHz VLBA polarimetric observations of relativistic jets in active galactic nuclei (the MOJAVE-2 project) are analyzed. We compare characteristics of VLBI features with jet model predictions and test if adiabatic expansion is a dominating mechanism for the evolution of relativistic shocks in parsec-scale AGN jets. We also discuss magnetic field configuration, both predicted by the model and deduced from electric vector position angle measurements.
Shinnaga, Hiroko; Phillips, Thomas G. [California Institute of Technology Submillimeter Observatory, 111 Nowelo Street, Hilo, HI 96720 (United States); Novak, Giles [Department of Physics and Astronomy, Northwestern University, 633 Clark Street Evanston, IL 60208 (United States); Vaillancourt, John E. [Stratospheric Observatory for Infrared Astronomy, Universities Space Research Association, NASA Ames Research Center, Moffet Field, CA 94035 (United States); Machida, Masahiro N. [Department of Earth and Planetary Sciences, Faculty of Sciences, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581 (Japan); Kataoka, Akimasa [Department of Astronomy, Kyoto University, Kitashirakawa-Oiwake-cho, Sakyo-ku, Kyoto 606-8502 (Japan); Tomisaka, Kohji [National Astronomical Observatory of Japan and Department of Astronomy, School of Physical Sciences, Graduate University for Advanced Studies (SOKENDAI), Osawa 2-21-1, Mitaka, Tokyo 181-8588 (Japan); Davidson, Jacqueline; Houde, Martin [School of Physics, University of Western Australia, 35 Stirling Highway, Crawley WA 6009, Perth (Australia); Dowell, C. Darren [Jet Propulsion Laboratory, California Institute of Technology, MS 169-506, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States); Leeuw, Lerothodi [SETI Institute, 515 North Whisman Avenue, Mountain View, CA 94043 (United States)
We measured polarized dust emission at 350 {mu}m toward the high-mass star-forming massive dense clump IRAS 20126+4104 using the SHARC II Polarimeter, SHARP, at the Caltech Submillimeter Observatory. Most of the observed magnetic field vectors agree well with magnetic field vectors obtained from a numerical simulation for the case when the global magnetic field lines are inclined with respect to the rotation axis of the dense clump. The results of the numerical simulation show that rotation plays an important role on the evolution of the massive dense clump and its magnetic field. The direction of the cold CO 1-0 bipolar outflow is parallel to the observed magnetic field within the dense clump as well as the global magnetic field, as inferred from optical polarimetry data, indicating that the magnetic field also plays a critical role in an early stage of massive star formation. The large-scale Keplerian disk of the massive (proto)star rotates in an almost opposite sense to the clump's envelope. The observed magnetic field morphology and the counterrotating feature of the massive dense clump system provide hints to constrain the role of magnetic fields in the process of high-mass star formation.
Graphene transparency in weak magnetic fields
David Valenzuela; Sa·l Hernßndez-Ortiz; Marcelo Loewe; Alfredo Raya
We carry out an explicit calculation of the vacuum polarization tensor for an effective low-energy model of monolayer graphene in the presence of a weak magnetic field of intensity $B$ perpendicularly aligned to the membrane. By expanding the quasiparticle propagator in the Schwinger proper time representation up to order $(eB)^2$, where $e$ is the unit charge, we find an explicitly transverse tensor, consistent with gauge invariance. Furthermore, assuming that graphene is radiated with monochromatic light of frequency $\\omega$ along the external field direction, from the modified Maxwell's equations we derive the intensity of transmitted light and the angle of polarization rotation in terms of the longitudinal ($\\sigma_{xx}$) and transverse ($\\sigma_{xy}$) conductivities. Corrections to these quantities, both calculated and measured, are of order $(eB)^2/\\omega^4$. Our findings generalize and complement previously known results reported in literature regarding the light absorption problem in graphene from the experimental and theoretical points of view, with and without external magnetic fields.
Rotating-frame gradient fields for magnetic resonance imaging and nuclear magnetic resonance in low fields
Bouchard, Louis-Serge; Pines, Alexander; Demas, Vasiliki
A system and method for Fourier encoding a nuclear magnetic resonance (NMR) signal is disclosed. A static magnetic field B.sub.0 is provided along a first direction. An NMR signal from the sample is Fourier encoded by applying a rotating-frame gradient field B.sub.G superimposed on the B.sub.0, where the B.sub.G comprises a vector component rotating in a plane perpendicular to the first direction at an angular frequency .omega.in a laboratory frame. The Fourier-encoded NMR signal is detected.
Magnetic fields in relativistic collisionless shocks
Santana, Rodolfo; Kumar, Pawan [Department of Astronomy, University of Texas at Austin, Austin, TX 78712 (United States); Barniol Duran, Rodolfo, E-mail: email@example.com, E-mail: email@example.com, E-mail: email@example.com [Racah Institute for Physics, The Hebrew University, Jerusalem 91904 (Israel)
We present a systematic study on magnetic fields in gamma-ray burst (GRB) external forward shocks (FSs). There are 60 (35) GRBs in our X-ray (optical) sample, mostly from Swift. We use two methods to study ? {sub B} (fraction of energy in magnetic field in the FS): (1) for the X-ray sample, we use the constraint that the observed flux at the end of the steep decline is ? X-ray FS flux; (2) for the optical sample, we use the condition that the observed flux arises from the FS (optical sample light curves decline as ?t {sup ¢1}, as expected for the FS). Making a reasonable assumption on E (jet isotropic equivalent kinetic energy), we converted these conditions into an upper limit (measurement) on ? {sub B} n {sup 2/(p+1)} for our X-ray (optical) sample, where n is the circumburst density and p is the electron index. Taking n = 1 cm{sup ¢3}, the distribution of ? {sub B} measurements (upper limits) for our optical (X-ray) sample has a range of ?10{sup ¢8}-10{sup ¢3} (?10{sup ¢6}-10{sup ¢3}) and median of ?few ū 10{sup ¢5} (?few ū 10{sup ¢5}). To characterize how much amplification is needed, beyond shock compression of a seed magnetic field ?10 ?G, we expressed our results in terms of an amplification factor, AF, which is very weakly dependent on n (AF?n {sup 0.21}). The range of AF measurements (upper limits) for our optical (X-ray) sample is ?1-1000 (?10-300) with a median of ?50 (?50). These results suggest that some amplification, in addition to shock compression, is needed to explain the afterglow observations.
SQUID-Detected Magnetic Resonance Imaging in MicroteslaFields
Moessle, Michael; Hatridge, Michael; Clarke, John
Magnetic resonance imaging (MRI) has developed into a powerful clinical tool for imaging the human body (1). This technique is based on nuclear magnetic resonance (NMR) of protons (2, 3) in a static magnetic field B{sub 0}. An applied radiofrequency pulse causes the protons to precess about B{sub 0} at their Larmor frequency {nu}{sub 0} = ({gamma}/2{pi})B{sub 0}, where {gamma} is the gyromagnetic ratio; {gamma}/2{pi} = 42.58 MHz/tesla. The precessing protons generate an oscillating magnetic field and hence a voltage in a nearby coil that is amplified and recorded. The application of three-dimensional magnetic field gradients specifies a unique magnetic field and thus an NMR frequency in each voxel of the subject, so that with appropriate encoding of the signals one can acquire a complete image (4). Most clinical MRI systems involve magnetic fields generated by superconducting magnets, and the current trend is to higher magnetic fields than the widely used 1.5-T systems (5). Nonetheless, there is ongoing interest in the development of less expensive imagers operating at lower fields. Commercially available 0.2-T systems based on permanent magnets offer both lower cost and a more open access than their higher-field counterparts, at the expense of signal-to-noise-ratio (SNR) and spatial resolution. At the still lower field of 0.03 mT maintained by a conventional, room-temperature solenoid, Connolly and co-workers (6, 7) obtain good spatial resolution and signal-to-noise ratio (SNR) by prepolarizing the protons in a field B{sub p} of 0.3 T. Prepolarization (8) enhances the magnetic moment of an ensemble of protons over that produced by the lower precession field; after the polarizing field is removed, the higher magnetic moment produces a correspondingly larger signal during its precession in B{sub 0}. Using the same method, Stepisnik et al. (9) obtained MR images in the Earth's magnetic field ({approx} 50 {micro}T). Alternatively, one can enhance the signal amplitude in MRI using laser polarized noble gases such as {sup 3}He or {sup 129}Xe (10-12). Hyperpolarized gases were used successfully to image the human lung in fields on the order of several mT (13-15). To overcome the sensitivity loss of Faraday detection at low frequencies, ultrasensitive magnetometers based on the Superconducting QUantum Interference Device (SQUID) (16) are used to detect NMR and MRI signals (17-24). Recently, SQUID-based MRI systems capable of acquiring in vivo images have appeared. For example, in the 10-mT system of Seton et al. (18) signals are coupled to a SQUID via a superconducting tuned circuit, while Clarke and coworkers (22, 25, 26) developed a system at 132 {micro}T with an untuned input circuit coupled to a SQUID. In a quite different approach, atomic magnetometers have been used recently to detect the magnetization (27) and NMR signal (28) of hyperpolarized gases. This technique could potentially be used for low-field MRI in the future. The goal of this review is to summarize the current state-of-the-art of MRI in microtesla fields detected with SQUIDs. The principles of SQUIDs and NMR are briefly reviewed. We show that very narrow NMR linewidths can be achieved in low magnetic fields that are quite inhomogeneous, with illustrative examples from spectroscopy. After describing our ultralow-field MRI system, we present a variety of images. We demonstrate that in microtesla fields the longitudinal relaxation T{sub 1} is much more material dependent than is the case in high fields; this results in a substantial improvement in 'T{sub 1}-weighted contrast imaging'. After outlining the first attempts to combine microtesla NMR with magnetoencephalography (MEG) (29), we conclude with a discussion of future directions.
On the delayed gas breakdown in a ringing theta-pinch with bias magnetic field
Meeks, Warner C.; Rovey, Joshua L. [Mechanical and Aerospace Engineering, Missouri University of Science and Technology, Rolla, Missouri 65409-0050 (United States)
A single particle model and particle-in-cell simulations are used to elucidate the breakdown physics in a ringing theta-pinch with a bias magnetic field. Previous experimental results show that gas breakdown occurs when the bias magnetic field is nullified by the theta-pinch magnetic field. The analyses presented here agree with the experimental results and show that electron kinetic energy does not exceed the ionization threshold of deuterium until the net magnetic field is approximately zero. Despite the presence of a strong electric field, the gyromotion of electrons within the bias magnetic field prevents them from gaining energy necessary to ionize the gas. Parametric analysis of the peak electron energy as a function of the bias and pre-ionization magnetic fields reveals that: (1) when the bias magnetic field is Almost-Equal-To 97% of the pre-ionization magnetic field, peak electron energies are highly erratic resulting in poor overall ionization, and (2) full ionization with repeatable behavior requires a pre-ionization to bias magnetic field ratio of approximately 2 to 1 or higher.
Dispersion relation and growth rate in a Cherenkov free electron laser: Finite axial magnetic field
Kheiri, Golshad; Esmaeilzadeh, Mahdi [Department of Physics, Iran University of Science and Technology, Tehran 16844 (Iran, Islamic Republic of)] [Department of Physics, Iran University of Science and Technology, Tehran 16844 (Iran, Islamic Republic of)
A theoretical analysis is presented for dispersion relation and growth rate in a Cherenkov free electron laser with finite axial magnetic field. It is shown that the growth rate and the resonance frequency of Cherenkov free electron laser increase with increasing axial magnetic field for low axial magnetic fields, while for high axial magnetic fields, they go to a saturation value. The growth rate and resonance frequency saturation values are exactly the same as those for infinite axial magnetic field approximation. The effects of electron beam self-fields on growth rate are investigated, and it is shown that the growth rate decreases in the presence of self-fields. It is found that there is an optimum value for electron beam density and Lorentz relativistic factor at which the maximum growth rate can take place. Also, the effects of velocity spread of electron beam are studied and it is found that the growth rate decreases due to the electron velocity spread.
Large-scale magnetic fields in the inflationary universe
Kazuharu Bamba; Misao Sasaki
The generation of large-scale magnetic fields is studied in inflationary cosmology. We consider the violation of the conformal invariance of the Maxwell field by dilatonic as well as non-minimal gravitational couplings. We derive a general formula for the spectrum of large-scale magnetic fields for a general form of the coupling term and the formula for the spectral index. The result tells us clearly the (necessary) condition for the generation of magnetic fields with sufficiently large amplitude.
Collective Modes of Chiral Kinetic Theory in Magnetic Field
Mikhail Stephanov; Ho-Ung Yee; Yi Yin
We study collective excitations in systems described by chiral kinetic theory in external magnetic field. We consider high-temperature weak-coupling plasma, as well as high-density Landau Fermi liquid with interaction not restricted to be weak. We show that chiral magnetic wave (CMW) emerges in hydrodynamic regime (at frequencies smaller than collision relaxation rate) and the CMW velocity is determined by thermodynamic properties only. We find that in a plasma of opposite chiralities, at frequencies smaller than the chirality-flipping rate, the CMW excitation turns into a vector-like diffusion mode. In the interacting Fermi liquid, the CMW turns into the Landau zero sound mode in the high-frequency collisionless regime.
Collective Modes of Chiral Kinetic Theory in Magnetic Field
Stephanov, Mikhail; Yin, Yi
We study collective excitations in systems described by chiral kinetic theory in external magnetic field. We consider high-temperature weak-coupling plasma, as well as high-density Landau Fermi liquid with interaction not restricted to be weak. We show that chiral magnetic wave (CMW) emerges in hydrodynamic regime (at frequencies smaller than collision relaxation rate) and the CMW velocity is determined by thermodynamic properties only. We find that in a plasma of opposite chiralities, at frequencies smaller than the chirality-flipping rate, the CMW excitation turns into a vector-like diffusion mode. In the interacting Fermi liquid, the CMW turns into the Landau zero sound mode in the high-frequency collisionless regime.
Chapman, Nicholas L.; Goldsmith, Paul F.; Pineda, Jorge L.; Li Di [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, MS 301-429, Pasadena, CA 91109 (United States); Clemens, D. P. [Institute for Astrophysical Research, Boston University, 725 Commonwealth Avenue, Boston, MA 02215 (United States); Krco, Marko, E-mail: firstname.lastname@example.com [Department of Astronomy, Cornell University, Ithaca, NY 14853 (United States)
We present maps of the plane-of-sky magnetic field within two regions of the Taurus molecular cloud: one in the dense core L1495/B213 filament and the other in a diffuse region to the west. The field is measured from the polarization of background starlight seen through the cloud. In total, we measured 287 high-quality near-infrared polarization vectors in these regions. In L1495/B213, the percent polarization increases with column density up to A{sub V} {approx} 9 mag, the limits of our data. The radiative torques model for grain alignment can explain this behavior, but models that invoke turbulence are inconsistent with the data. We also combine our data with published optical and near-infrared polarization measurements in Taurus. Using this large sample, we estimate the strength of the plane-of-sky component of the magnetic field in nine subregions. This estimation is done with two different techniques that use the observed dispersion in polarization angles. Our values range from 5 to 82 {mu}G and tend to be higher in denser regions. In all subregions, the critical index of the mass-to-magnetic flux ratio is sub-unity, implying that Taurus is magnetically supported on large scales ({approx}2 pc). Within the region observed, the B213 filament takes a sharp turn to the north and the direction of the magnetic field also takes a sharp turn, switching from being perpendicular to the filament to becoming parallel. This behavior can be understood if we are observing the rim of a bubble. We argue that it has resulted from a supernova remnant associated with a recently discovered nearby gamma-ray pulsar.
Enhanced density and magnetic fields in interstellar OH masers
Vincent L. Fish; Mark J. Reid; Karl M. Menten; Thushara Pillai
Aims: We have observed the 6030 and 6035 MHz transitions of OH in high-mass star-forming regions to obtain magnetic field estimates in both maser emission and absorption. Methods: Observations were taken with the Effelsberg 100 m telescope. Results: Our observations are consistent with previous results, although we do detect a new 6030 MHz maser feature near -70 km/s in the vicinity of W3(OH). In absorption we obtain a possible estimate of -1.1 +/- 0.3 mG for the average line-of-sight component of the magnetic field in the absorbing OH gas in K3-50 and submilligauss upper limits for the line-of-sight field strength in DR 21 and W3. Conclusions: These results indicate that the magnetic field strength in the vicinity of OH masers is higher than that of the surrounding, non-masing material, which in turn suggests that the density of masing OH regions is higher than that of their surroundings.
Proposal for high-speed and high-fidelity electron-spin initialization in a negatively charged quantum dot coupled to a microcavity in a weak external magnetic field
Majumdar, Arka; Lin Ziliang; Faraon, Andrei; Vuckovic, Jelena [E. L. Ginzton Laboratory, Stanford University, Stanford, California 94305 (United States)
We describe a proposal for fast electron-spin initialization in a negatively charged quantum dot coupled to a microcavity without the need for a strong magnetic field. We employ two-photon excitation to access trion states that are spin forbidden by one-photon excitation. Our simulation shows a maximum initialization speed of 1.3 GHz and maximum fidelity of 99.7% with realistic system parameters.
SU-E-J-233: A Facility for Radiobiological Experiments in a Large Magnetic Field
Carlone, M; Heaton, R; Keller, H [Princess Margaret Hospital, Toronto, ON (Canada); University of Toronto, Toronto, ON (Canada); Wouters, B [Ontario Cancer Institute, Toronto, ON (Canada); University of Toronto, Toronto, ON (Canada); Jaffray, D [Princess Margaret Hospital, Toronto, ON (Canada); Ontario Cancer Institute, Toronto, ON (Canada); University of Toronto, Toronto, ON (Canada)
Purpose: There is considerable interest in developing medical linear accelerators with integrated image guidance by MRI. Less work has been done on the fundamental biology of cell survival in the presence of a strong magnetic field. The purpose of this work is to describe an experimental system capable of measuring cell survival response in the types of MRI-linac systems currently under development. Methods: We have integrated a cobalt irradiator with a solenoid magnet. The solenoid magnet has inner diameter of 10 cm. To enable measurement of the biological effects as a function of depth, we are utilizing the sliced gel technique, in which cells are embedded and fixed within a gelatin matrix. Irradiated cells at defined positions (sub mm resolution) can subsequently be recovered and assessed for cell survival or other biological effects. Results: The magnetic field profile in the solenoid has a peak magnetic field 36 cm below the top edge of the magnet bore and can be placed at and SAD of 100 cm. At a solenoid current of 35 A, the peak magnetic field is 0.25 T. The dose rate of the cobalt irradiator is 16 cGy/min at 100 cm SAD. EBT3 film was used to demonstrate the system functionality. It was irradiated at 1 cm depth at 100 cm SSD with a 4ū4 field to 1.5 Gy in a 0.25 T magnetic field. The dose profile was similar between this film and the control exposure without magnetic field. Conclusion: Integrating a cobalt irradiator with a high field magnet is demonstrated. The magnetic field at the cobalt defining head was minimal and did not interfere with the functioning of this unit. Cell survival experiments can be reproduced exactly in the presence or absence of a magnetic field since a resistive magnet is used.
Neutron scattering in magnetic fields (*) W. C. Koehler
Boyer, Edmond
691 Neutron scattering in magnetic fields (*) W. C. Koehler Solid State Division, Oak Ridge. Abstract 2014 The use of magnetic fields in neutron scattering experimentation is reviewed briefly. Two of the scattering sample ; in the second the field acts on the neutron itself. Several examples are discussed
Magnetic Propulsion of Intense Lithium Streams in a Tokamak Magnetic Field
Zakharov, Leonid E.
Magnetic Propulsion of Intense Lithium Streams in a Tokamak Magnetic Field Leonid E. Zakharov the theory of magnetic propulsion of liquid lithium streams and their stability in tokamaks takes into account the propulsion e#11;ect, viscosity and the drag force due to magnetic pumping
Baryon magnetic moments in the background field method
Lee, F X; Zhou, L; Wilcox, W
We present a calculation of the magnetic moments for the baryon octet and decuplet using the background-field method and standard Wilson gauge and fermion actions in the quenched approximation of lattice QCD. Progressively smaller static magnetic fields are introduced on a $24^4$ lattice at beta=6.0 and the pion mass is probed down to about 500 MeV. Magnetic moments are extracted from the linear response of the masses to the background field.
Baryon magnetic moments in the external field method
Lee, F X; Zhou, L; Wilcox, W
We present a calculation of the magnetic moments of the baryon octet and decuplet using the external field method and standard Wilson gauge and fermion actions in the quenched approximation. Progressively smaller static magnetic fields are introduced on a $24^4$ latticeat beta=6.0 and the pion mass is probed down to about 500 MeV. Magnetic moments are extracted from the linear response of the masses to the external field.
Temperature compensated current sensor using reference magnetic field
Yakymyshyn, Christopher Paul (Seminole, FL); Brubaker, Michael Allen (Loveland, CO); Yakymyshyn, Pamela Jane (Seminole, FL)
A method is described to provide temperature compensation and self-calibration of a current sensor based on a plurality of magnetic field sensors positioned around a current carrying conductor. A reference magnetic field generated within the current sensor housing is detected by a separate but identical magnetic field sensor and is used to correct variations in the output signal due to temperature variations and aging.
The St³ckelberg Holographic Superconductors in Constant External Magnetic Field
Jian-Pin Wu
We investigate the St\\"{u}ckelberg holographic superconductor in present of the constant external magnetic field. We observe that a critical value of magnetic field exists as the cases in usual holographic superconductor. Furthermore, we find that the applied magnetic field strongly influence the phase transition of this model and have a jump in the condensate at the critical temperature even for $c_{4}=1$.
High field magnetotransport and point contact Andreev reflection measurements on CuCr{sub 2}Se{sub 4} and CuCr{sub 2}Se{sub 3}BrŚDegenerate magnetic semiconductor single crystals
Borisov, K., E-mail: firstname.lastname@example.com; Coey, J. M. D.; Stamenov, P. [School of Physics and CRANN, Trinity College, Dublin 2 (Ireland); Alaria, J. [Department of Physics, University of Liverpool, Liverpool L69 7ZE (United Kingdom)
Single crystals of the metallically degenerate fully magnetic semiconductors CuCr{sub 2}Se{sub 4} and CuCr{sub 2}Se{sub 3}Br have been prepared by the Chemical Vapour Transport method, using either Se or Br as transport agents. The high-quality, millimetre-sized, octahedrally faceted, needle- and platelet-shaped crystals are characterised by means of high field magnetotransport (?{sub 0}H? 14?T) and Point Contact Andreev Reflection. The relatively high spin polarisation observed |P|>0.56, together with the relatively low minority carrier effective mass of 0.25 m{sub e}, and long scattering time Ā10{sup ?13}?s, could poise these materials for integration in low- and close-to-room temperature minority injection bipolar heterojunction transistor demonstrations.
Testing a Solar Coronal Magnetic Field Extrapolation Code with the Titov-Demoulin Magnetic Flux Rope Model
Jiang, Chaowei
In the solar corona, magnetic flux rope is believed to be a fundamental structure accounts for magnetic free energy storage and solar eruptions. Up to the present, the extrapolation of magnetic field from boundary data is the primary way to obtain fully three-dimensional magnetic information of the corona. As a result, the ability of reliable recovering coronal magnetic flux rope is important for coronal field extrapolation. In this paper, our coronal field extrapolation code (CESE-MHD-NLFFF, Jiang & Feng 2012) is examined with an analytical magnetic flux rope model proposed by Titov & Demoulin (1999), which consists of a bipolar magnetic configuration holding an semi-circular line-tied flux rope in force-free equilibrium. By using only the vector field in the bottom boundary as input, we test our code with the model in a representative range of parameter space and find that the model field is reconstructed with high accuracy. Especially, the magnetic topological interfaces formed between the flux rop...
Static magnetic field concentration and enhancement using magnetic materials with positive permeability
Sun, F
In this paper a novel compressor for static magnetic fields is proposed based on finite embedded transformation optics. When the DC magnetic field passes through the designed device, the magnetic field can be compressed inside the device. After it passes through the device, one can obtain an enhanced static magnetic field behind the output surface of the device (in a free space region). We can also combine our compressor with some other structures to get a higher static magnetic field enhancement in a free space region. In contrast with other devices based on transformation optics for enhancing static magnetic fields, our device is not a closed structure and thus has some special applications (e.g., for controlling magnetic nano-particles for gene and drag delivery). The designed compressor can be constructed by using currently available materials or DC meta-materials with positive permeability. Numerical simulation verifies good performance of our device.
Electrostatic and Magnetic Fields in Bilayer Graphene
Ahmed Jellal; Ilham Redouani; Hocine Bahlouli
We compute the transmission probability through rectangular potential barriers and p-n junctions in the presence of a magnetic and electric fields in bilayer graphene taking into account the full four bands of the energy spectrum. For energy E higher than the interlayer coupling $\\gamma_1 (E>\\gamma_1)$ two propagation modes are available for transport giving rise to four possible ways for transmission and reflection probabilities. However, when the energy is less then the height of the barrier the Dirac fermions exhibits transmission resonances and only one mode of propagation is available. We study the effect of the interlayer electrostatic potential $\\delta$ and the different geometry parameters of the barrier on the transmission probability.
Heat pulse propagation in chaotic three-dimensional magnetic fields
Del-Castillo-Negrete, Diego [Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States); Blazevski, Daniel [Institute for Mechanical Systems, ETH, Zurich (Switzerland)
Heat pulse propagation in three-dimensional chaotic magnetic fields is studied by numerically solving the parallel heat transport equation using a Lagrangian Green's function (LG) method. The main two problems addressed are: the dependence of the radial transport of heat pulses on the level of magnetic field stochasticity (controlled by the amplitude of the magnetic field perturbation, ?), and the role of reversed shear magnetic field configurations on heat pulse propagation. The role of separatrix reconnection of resonant modes in the shear reversal region, and the role of shearless Cantori in the observed phenomena are also discussed.
Coulomb law and energy levels in a superstrong magnetic field
Vysotsky, M I
Analytical expression for the Coulomb potential in the presence of superstrong magnetic field is derived. Structure of hydrogen levels originating from LLL is analyzed.
Entanglement of two-qubit photon beam by magnetic field
A. D. Levin; D. M. Gitman; R. C. Castro
We have studied the possibility of affecting the entanglement measure of 2-qubit system consisting of two photons with different fixed frequencies but with two arbitrary linear polarizations, moving in the same direction, by the help of an applied external magnetic field. The interaction between the magnetic field and the photons in our model is achieved through intermediate electrons that interact with both the photons and the magnetic field. The possibility of exact theoretical analysis of this scheme is based on known exact solutions that describe the interaction of an electron subjected to an external magnetic field (or a medium of electrons not interacting with each other) with a quantized field of two photons. We adapt these exact solutions to the case under consideration. Using explicit wave functions for the resulting electromagnetic field, we calculate the entanglement measure of the photon beam as a function of the applied magnetic field and parameters of the electron medium.
How are Forbush decreases related with interplanetary magnetic field enhancements ?
Arunbabu, K P; Dugad, S R; Gupta, S K; Hayashi, Y; Kawakami, S; Mohanty, P K; Oshima, A; Subramanian, P
Aims. Forbush decrease (FD) is a transient decrease followed by a gradual recovery in the observed galactic cosmic ray intensity. We seek to understand the relationship between the FDs and near-Earth interplanetary magnetic field (IMF) enhancements associated with solar coronal mass ejections (CMEs). Methods. We use muon data at cutoff rigidities ranging from 14 to 24 GV from the GRAPES-3 tracking muon telescope to identify FD events. We select those FD events that have a reasonably clean profile, and magnitude > 0.25%. We use IMF data from ACE/WIND spacecrafts. We look for correlations between the FD profile and that of the one hour averaged IMF. We ask if the diffusion of high energy protons into the large scale magnetic field is the cause of the lag observed between the FD and the IMF. Results. The enhancement of the IMF associated with FDs occurs mainly in the shock-sheath region, and the turbulence level in the magnetic field is also enhanced in this region. The observed FD profiles look remarkably simil...
Quantum interference effects in a strongly fluctuating magnetic field G. M. Gusev,* U. Gennser,
Gusev, Guennady
. Kleber, D. K. Maude, and J. C. Portal High Magnetic Field LaboratoryŁCNRS, Boi^te Postale 166, F-38042, Siberian Branch, Novosibirsk, Russia Received 6 November 1995 We have studied the negative
Development of Apple Workgroup Cluster and Parallel Computing for Phase Field Model of Magnetic MaterialsĀ
Huang, Yongxin
using MPI. The results show the cluster system can simultaneously support up to 32 processes for MPI program with high performance of interprocess communication. The parallel computations of phase field model of magnetic materials implemented by a MPI...
Structure, dynamical impact and origin of magnetic fields in nearby galaxies in the SKA era
Beck, Rainer; Colafrancesco, Sergio; Dettmar, Ralf-J³rgen; FerriĶre, Katia; Fletcher, Andrew; Heald, George; Heesen, Volker; Horellou, Cathy; Krause, Marita; Lou, Yu-Qing; Mao, Sui Ann; Paladino, Rosita; Schinnerer, Eva; Sokoloff, Dmitry; Stil, Jeroen; Tabatabaei, Fatemeh
Magnetic fields are an important ingredient of the interstellar medium (ISM). Besides their importance for star formation, they govern the transport of cosmic rays, relevant to the launch and regulation of galactic outflows and winds, which in turn are pivotal in shaping the structure of halo magnetic fields. Mapping the small-scale structure of interstellar magnetic fields in many nearby galaxies is crucial to understand the interaction between gas and magnetic fields, in particular how gas flows are affected. Elucidation of the magnetic role in, e.g., triggering star formation, forming and stabilising spiral arms, driving outflows, gas heating by reconnection and magnetising the intergalactic medium has the potential to revolutionise our physical picture of the ISM and galaxy evolution in general. Radio polarisation observations in the very nearest galaxies at high frequencies (>= 3 GHz) and with high spatial resolution (<= 5") hold the key here. The galaxy survey with SKA1 that we propose will also be a...
A loss-based, magnetic field sensor implemented in a ferrofluid infiltrated microstructured polymer optical fiber
Candiani, A. [Foundation for Research and Technology-Hellas (FORTH), Institute of Electronic Structure and Laser (IESL), Heraklion 70013 Greece (Greece); Department of Information Engineering (DII), University of Parma, Parma 43124 (Italy); Argyros, A.; Leon-Saval, S. G.; Lwin, R. [Institute of Photonics and Optical Science (IPOS), School of Physics, The University of Sydney, Sydney (Australia); Selleri, S. [Department of Information Engineering (DII), University of Parma, Parma 43124 (Italy); Pissadakis, S., E-mail: email@example.com [Foundation for Research and Technology-Hellas (FORTH), Institute of Electronic Structure and Laser (IESL), Heraklion 70013 Greece (Greece)
We report an in-fiber magnetic field sensor based on magneto-driven optical loss effects, while being implemented in a ferrofluid infiltrated microstructured polymer optical fiber. We demonstrate that magnetic field flux changes up to 2000 gauss can be detected when the magnetic field is applied perpendicular to the fiber axis. In addition, the sensor exhibits high polarization sensitivity for the interrogated wavelengths, providing the possibility of both field flux and direction measurements. The underlying physical and guidance mechanisms of this sensing transduction are further investigated using spectrophotometric, light scattering measurements, and numerical simulations, suggesting photonic Hall effect as the dominant physical, transducing mechanism.
Primary beam steering due to field leakage from superconducting SHMS magnets
DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)
Moore, M.H.; Waidyawansa, B.P.; Covrig, S.; Carlini, R.; Benesch, J.
Simulations of the magnetic fields from the Super High Momentum Spectrometer in Hall C at Thomas Jefferson National Accelerator Facility show significant field leakage into the region of the primary beam line between the target and the beam dump. Without mitigation, these remnant fields will steer the unscattered beam enough to limit beam operations at small scattering angles. Presented here are magnetic field simulations of the spectrometer magnets and a solution using optimal placement of a minimal amount of shielding iron around the beam line.
Primary Beam Steering Due to Field Leakage from Superconducting SHMS Magnets
Michael H. Moore; Buddhini P. Waidyawansa; Silviu Covrig; Roger Carlini; Jay Benesch
Simulations of the magnetic fields from the Super High Momentum Spectrometer in Hall C at Thomas Jefferson National Accelerator Facility show significant field leakage into the region of the primary beam line between the target and the beam dump. Without mitigation, these remnant fields will steer the unscattered beam enough to limit beam operations at small scattering angles. Presented here are magnetic field simulations of the spectrometer magnets and a solution using optimal placement of a minimal amount of shielding iron around the beam line.
Guo Fan; Li Shengtai; Li Hui; Li, David [Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Giacalone, Joe; Jokipii, J. R. [Department of Planetary Sciences and Lunar and Planetary Laboratory, University of Arizona, 1629 E. University Blvd., Tucson, AZ 85721 (United States)
We have performed extensive two-dimensional magnetohydrodynamic simulations to study the amplification of magnetic fields when a supernova blast wave propagates into a turbulent interstellar plasma. The blast wave is driven by injecting high pressure in the simulation domain. The interstellar magnetic field can be amplified by two different processes, occurring in different regions. One is facilitated by the fluid vorticity generated by the 'rippled' shock front interacting with the background turbulence. The resulting turbulent flow keeps amplifying the magnetic field, consistent with earlier work. The other process is facilitated by the growth of the Rayleigh-Taylor instability at the contact discontinuity between the ejecta and the shocked medium. This can efficiently amplify the magnetic field and tends to produce the highest magnetic field. We investigate the dependence of the amplification on numerical parameters such as grid-cell size and on various physical parameters. We show that the magnetic field has a characteristic radial profile such that the downstream magnetic field gets progressively stronger away from the shock. This is because the downstream magnetic field needs a finite time to reach the efficient amplification, and will get further amplified in the Rayleigh-Taylor region. In our simulation, we do not observe a systematic strong magnetic field within a small distance to the shock. This indicates that if the magnetic-field amplification in supernova remnants indeed occurs near the shock front, other processes such as three-dimensional instabilities, plasma kinetics, and/or cosmic ray effect may need to be considered to explain the strong magnetic field in supernova remnants.
Observation of low magnetic field density peaks in helicon plasma
Barada, Kshitish K.; Chattopadhyay, P. K.; Ghosh, J.; Kumar, Sunil; Saxena, Y. C. [Institute for Plasma Research, Bhat, Gandhinagar 382428 (India)
Single density peak has been commonly observed in low magnetic field (<100 G) helicon discharges. In this paper, we report the observations of multiple density peaks in low magnetic field (<100 G) helicon discharges produced in the linear helicon plasma device [Barada et al., Rev. Sci. Instrum. 83, 063501 (2012)]. Experiments are carried out using argon gas with m = +1 right helical antenna operating at 13.56 MHz by varying the magnetic field from 0 G to 100 G. The plasma density varies with varying the magnetic field at constant input power and gas pressure and reaches to its peak value at a magnetic field value of {approx}25 G. Another peak of smaller magnitude in density has been observed near 50 G. Measurement of amplitude and phase of the axial component of the wave using magnetic probes for two magnetic field values corresponding to the observed density peaks indicated the existence of radial modes. Measured parallel wave number together with the estimated perpendicular wave number suggests oblique mode propagation of helicon waves along the resonance cone boundary for these magnetic field values. Further, the observations of larger floating potential fluctuations measured with Langmuir probes at those magnetic field values indicate that near resonance cone boundary; these electrostatic fluctuations take energy from helicon wave and dump power to the plasma causing density peaks.
Measuring and shimming the magnetic field of a 4 Tesla MRI magnet
Kyriazis, Georgios
The Biomedical Magnetic Resonance Laboratory (BMRL) of the University of Illinois at Urbana-Champaign (UIUC) has ordered from the Texas Accelerator Center (TAC) a superconducting, self-shielded, solenoidal magnet with a maximum field of 4 Tesla...
Magnetic field-induced phase transformation & power harvesting capabilities in magnetic shape memory alloys
Basaran, Burak
Magnetic Shape Memory Alloys (MSMAs) combine shape-change/deformationrecovery abilities of heat driven conventional shape memory alloys (SMA) and magnetic field driven magnetostrictives through martensitic transformation. They are promising...
Understanding magnetic field reversal mechanisms in mesoscopic magnetic multilayer ring structures
Ng, Bryan
Patterned pseudo spin-valve rings show great promise for device applications due to their non-volatility and variety of stable magnetic states. However, the magnetic reversal of these elements under an applied field is ...
The ionization rate under a general magnetic field for microwave breakdown
Wang, Huihui, E-mail: email@example.com; Meng, Lin; Liu, Dagang; Liu, Laqun [School of Physical Electronics, University of Electronic Science and Technology of China, Chengdu 610054 (China)
The ionization rate under an extra magnetic field is studied by theory and particle-in-cell/Monte Carlo Collision simulations. The result shows that a magnetic field always decreases the ionization rate if ?(3)???{sub m}, while it may increase the ionization rate if ?(3)??>??{sub m}. The effect of the magnetic field on the ionization rate fades away when the angle between the magnetic field and the electric filed approaches to zero. Furthermore, the peak ionization rate among different magnetic fields is almost independent of ?. This peak ionization rate is in direct proportion to the gas pressure in the low pressure region, while it is about in inverse proportion to the gas pressure in the high pressure region.
Nuclear magnetic absorption line widths in weak magnetic fields with a Robinson oscillator
Flugum, Timothy Lee
NUCLEAR MAGNETIC ABSORPTION LINE WIDTHS IN WEAK MAGNETIC FIELDS WITH A ROBINSON OSCILLATOR A Thesis by TIMOTHY LEE FLUGUM Subnntted to the Graduate College of Texas ARM University in partial fulfillment of the requirement for the degree... of MASTER OF SCIENCE August 19SI Major Subject: Physics NUCLEAR MAGNETIC ABSORPTION LINE WIDTHS IN WEAK MAGNETIC FIELDS WITH A ROBINSON OSCILLATOR A Thesis TIMOTHY LEE FLUGUM Approved as to style and content by: Nelson M. Duller (Chairman...
Development of magnetic separation methods of analysis: magnetic field flow fractionation
Garcia-Ramirez, Jaime
DEVELOPMENT OF MAGNETIC SEPARATION METHODS OF ANALYSIS: MAGNETIC FIELD FLOW FRACTIONATION A Thesis by JAIME GARCIA-RAMIREZ Submitted to the Graduate College of Texas A&M University in partial fulfillment of the requirement for the degree... of MASTER OF SCIENCE August 1980 Major Subject: Chemistry DEVELOPMENT OF MAGNETIC SEPARATION METHODS OF ANALYSIS: MAGNETIC FIELD FLOW FRACTIONATION A Thesis by JAIME GARCIA-RAMIREZ Approved as to style and content by: (Chairman of Committee) 1...
Including stereoscopic information in the reconstruction of coronal magnetic fields
T. Wiegelmann; T. Neukirch
We present a method to include stereoscopic information about the three dimensional structure of flux tubes into the reconstruction of the coronal magnetic field. Due to the low plasma beta in the corona we can assume a force free magnetic field, with the current density parallel to the magnetic field lines. Here we use linear force free fields for simplicity. The method uses the line of sight magnetic field on the photosphere as observational input. The value of $\\alpha$ is determined iteratively by comparing the reconstructed magnetic field with the observed structures. The final configuration is the optimal linear force solution constrained by both the photospheric magnetogram and the observed plasma structures. As an example we apply our method to SOHO MDI/EIT data of an active region. In the future it is planned to apply the method to analyse data from the SECCHI instrument aboard the STEREO mission.
Magnetic-field-induced antiferromagnetism in the Kondo lattice
Beach, Kevin S. D. (Kevin Stuart David), 1975-
The half-filled Kondo lattice model, augmented by a Zeeman term, serves as a useful model of a Kondo insulator in an applied magnetic field. A variational mean field analysis of this system on a square lattice, backed up ...
Field quality measurements of a 2-Tesla transmission line magnet
Velev, G.V.; Foster, W.; Kashikhin, V.; Mazur, P.; Oleck, A.; Piekarz, H.; Schlabach, P.; Sylvester, C.; /Fermilab; Wake, M.; /KEK, Tsukuba
A prototype 2-Tesla superconducting transmission line magnet for future hadron colliders was designed, built and tested at Fermilab. The 1.5 m long, combined-function gradient-dipole magnet has a vertical pole aperture of 20 mm. To measure the magnetic field quality in such a small magnet aperture, a specialized rotating coil of 15.2 mm diameter, 0.69 m long was fabricated. Using this probe, a program of magnetic field quality measurements was successfully performed. Results of the measurements are presented and discussed.
Strong magnetic fields and inhomogeneity in the solar corona
White, S.M.; Kundu, M.R.; Gopalswamy, N. (Maryland Univ., College Park (USA))
It is shown that fields of 1800 G can exist in the corona based on observations of gyroresonance emission at 15 GHz at coronal temperatures. The strong fields occur in a small source radiating in the extraordinary (x) mode over the penumbra of a large symmetric sunspot. The optically-thin ordinary mode emission from the region shows a nearby peak at only 36,000 K which may be due to a sunspot plume, and a hole over the umbra consistent with the expected low-density material there. The x-mode source is highly asymmetric, despite the apparent symmetry of the sunspot, and its appearance and location imply that the strongest magnetic fields in the corona are localized in a compact flux tube. 21 refs.
General relativistic simulations of black hole-neutron star mergers: Effects of magnetic fields
Zachariah B. Etienne; Yuk Tung Liu; Vasileios Paschalidis; Stuart L. Shapiro
As a neutron star (NS) is tidally disrupted by a black hole (BH) companion at the end of a BH-NS binary inspiral, its magnetic fields will be stretched and amplified. If sufficiently strong, these magnetic fields may impact the gravitational waveforms, merger evolution and mass of the remnant disk. Formation of highly-collimated magnetic field lines in the disk+spinning BH remnant may launch relativistic jets, providing the engine for a short-hard GRB. We analyze this scenario through fully general relativistic, magnetohydrodynamic (GRMHD) BHNS simulations from inspiral through merger and disk formation. Different initial magnetic field configurations and strengths are chosen for the NS interior for both nonspinning and moderately spinning (a/M=0.75) BHs aligned with the orbital angular momentum. Only strong interior (Bmax~10^17 G) initial magnetic fields in the NS significantly influence merger dynamics, enhancing the remnant disk mass by 100% and 40% in the nonspinning and spinning BH cases, respectively. However, detecting the imprint of even a strong magnetic field may be challenging for Advanced LIGO. Though there is no evidence of mass outflows or magnetic field collimation during the preliminary simulations we have performed, higher resolution, coupled with longer disk evolutions and different initial magnetic field configurations, may be required to definitively assess the possibility of BHNS binaries as short-hard GRB progenitors.
Earth's Magnetic Field Measurements for the LCLS Undulators
Hacker, Kirsten
Measurements of the earth's magnetic field at several locations at SLAC were conducted to determine the possible field error contribution from tuning the undulators in a location with a different magnetic field than that which will be found in the undulator hall. An average difference of 0.08 {+-} 0.04 Gauss has been measured between the downward earth's field components in the test facility and SLAC tunnel locations.
High-field remanence properties of synthetic and natural submicrometre haematites and goethites: significance
High-field remanence properties of synthetic and natural submicrometre haematites and goethites September 2004 Editor: V. Courtillot Abstract Haematite and goethite are significant magnetic components both of marine and terrestrial sediments. Variable magnetic behaviour in haematite and goethite has
Ultrasensitive magnetic field detection using a single artificial atom
Mustafa Bal; Chunqing Deng; Jean-Luc Orgiazzi; Florian Ong; Adrian Lupascu
Efficient detection of magnetic fields is central to many areas of research and has important practical applications ranging from materials science to geomagnetism. High sensitivity detectors are commonly built using direct current-superconducting quantum interference devices (DC-SQUIDs) or atomic systems. Here we use a single artificial atom to implement an ultrahigh sensitivity magnetometer with a size in the micron range. The artificial atom is a superconducting two-level system at low temperatures, operated in a way similar to atomic magnetometry. The high sensitivity results from quantum coherence combined with strong coupling to magnetic field. By employing projective measurements, we obtain a sensitivity of $2.7\\, \\t{pT}/\\sqrt{\\t{Hz}}$ at 10 MHz. We discuss feasible improvements that will increase the sensitivity by over one order of magnitude. The intrinsic sensitivity of this method to AC fields in the 100 kHz - 10 MHz range compares favourably with DC-SQUIDs and atomic magnetometers of equivalent spatial resolution. This result illustrates the potential of artificial quantum systems for sensitive detection and related applications.
Sidewall containment of liquid metal with vertical alternating magnetic fields
Lari, Robert J. (Aurora, IL); Praeg, Walter F. (Palos Park, IL); Turner, Larry R. (Naperville, IL); Battles, James E. (Oak Forest, IL); Hull, John R. (Hinsdale, IL); Rote, Donald M. (Lagrange, IL)
An apparatus for containing molten metal using a magnet producing vertical alternating magnetic field positioned adjacent the area in which the molten metal is to be confined. This invention can be adapted particularly to the casting of metal between counter-rotating rollers with the vertical alternating magnetic field used to confine the molten metal at the edges of the rollers. Alternately, the vertical alternating magnetic field can be used as a flow regulator in casting molten metal from an opening in a channel.
Dynamical Electron Mass in a Strong Magnetic Field
S. -Y. Wang
Motivated by recent interest in understanding properties of strongly magnetized matter, we study the dynamical electron mass generated through approximate chiral symmetry breaking in QED in a strong magnetic field. We reliably calculate the dynamical electron mass by numerically solving the nonperturbative Schwinger-Dyson equations in a consistent truncation within the lowest Landau level approximation. It is shown that the generation of dynamical electron mass in a strong magnetic field is significantly enhanced by the perturbative electron mass that explicitly breaks chiral symmetry in the absence of a magnetic field.
Stellar coronal magnetic fields and star-planet interaction
Lanza, A F
Evidence of magnetic interaction between late-type stars and close-in giant planets is provided by the observations of stellar hot spots rotating synchronously with the planets and showing an enhancement of chromospheric and X-ray fluxes. We investigate star-planet interaction in the framework of a magnetic field model of a stellar corona, considering the interaction between the coronal field and that of a planetary magnetosphere moving through the corona. The energy budget of the star-planet interaction is discussed assuming that the planet may trigger a release of the energy of the coronal field by decreasing its relative helicity. The observed intermittent character of the star-planet interaction is explained by a topological change of the stellar coronal field, induced by a variation of its relative helicity. The model predicts the formation of many prominence-like structures in the case of highly active stars owing to the accumulation of matter evaporated from the planet inside an azimuthal flux rope in ...
Submillimeter Polarimetry and the Galactic Center Magnetic Field
Novak, Giles
Submillimeter Polarimetry and the Galactic Center Magnetic Field D.T. Chuss NASA Goddard Space Flight Center C.D. Dowell Jet Propulsion Laboratory R.H. Hildebrand University of Chicago G. Novak that of the magnetic field. In addition, we present new Hertz data on the Dust Ridge, an arched structure
Magnetic field modulated dust streams from Jupiter in Interplanetary space
Hamilton, Douglas P.
Magnetic field modulated dust streams from Jupiter in Interplanetary space Alberto Flandes Ciencias┤es-Galicia Ciencias Espaciales, Instituto de Geof┤isica, UNAM, M┤exico. Linda Spilker Jet Propulsion Laboratory is sufficient to allow the planet's magnetic field to accelerate them away from the planet where
Complementary bowtie aperture for localizing and enhancing optical magnetic field
Xu, Xianfan
Complementary bowtie aperture for localizing and enhancing optical magnetic field Nan Zhou, Edward, 2011 Nanoscale bowtie antenna and bowtie aperture antenna have been shown to generate strongly enhanced. In this Letter, we discuss the enhancement of magnetic field intensity of nanoscale complementary bowtie aperture
Observation of magnetic field lines in the vicinity of a superconductor with the naked eye
Yoshihiko Saito
Meissner effect and pinning effect are clearly observed with the naked eye. A GdBaCuO high-temperature superconductor (HTS) disk fabricated by Nippon Steel Corporation, a 100mm cubic NdFeB sintered magnet, and iron wires coated by colored are used. When the HTS is put in the magnetic field of the magnet, it can be observed by the wires that the magnetic field lines are excluded from the superconductor (Meissner effect) as well as are pinned in the superconductor (pinning effect).
The Evolution of Cosmic Magnetic Fields: From the Very Early Universe, to Recombination, to the Present
Robi Banerjee; Karsten Jedamzik
(abridged) A detailed examination of the evolution of stochastic magnetic fields between high cosmic temperatures and the present epoch is presented. A simple analytical model matching the results of the 3D MHD simulations allows for the prediction of present day magnetic field correlation lengths and energy. Our conclusions are multi fold. (a) Initial primordial fields with only a small amount of helicity are evolving into maximally helical fields. (b) There exists a correlation between the strength of the magnetic field, B, at the peak of it's spectrum and the location of the peak, given at the present epoch by: B ~ 5x10^{-12} (L/kpc) Gauss, where L is the correlation length determined by the initial magnetic field. (c) Concerning studies of generation of cosmic microwave background (CMBR) anisotropies due to primordial magnetic fields of B~10^{-9} Gauss on ~ 10 Mpc scales, such fields are not only impossible to generate in early causal magnetogenesis scenarios but also seemingly ruled out by distortions of the CMBR spectrum due to magnetic field dissipation on smaller scales and the overproduction of cluster magnetic fields. (d) The most promising detection possibility of CMBR distortions due to primordial magnetic fields may be on much smaller scales at higher multipoles l~10^6 where the signal is predicted to be the strongest. (e) It seems possible that magnetic fields in clusters of galaxies are entirely of primordial origin, without invoking dynamo amplification. Such fields would be of (pre-collapse) strength 10^{-12} - 10^{-11} Gauss with correlation lengths in the kpc range, and would also exist in voids of galaxies.
Microwave magnetic dynamics in highly conducting magnetic nanostructures
Kostylev, M.; Ivanov, E.; Samarin, S. [School of Physics M013, The University of Western Australia, Crawley, WA 6009 (Australia); Ding, J.; Adeyeye, A. O. [Department of Electrical and Computer Engineering, National University of Singapore, Singapore 117576 (Singapore)
We performed low-noise broadband microstrip ferromagnetic resonance (FMR) measurements of the resonant modes of an array of metallic ferromagnetic nanostripes. In addition to a strong signal of the fundamental mode, we observed up to five weak-amplitude peaks in the field-resolved FMR traces, depending on the frequency. These higher-order absorption peaks have been theoretically identified as due to resonant excitation of odd and even standing spin waves across the direction of confinement in array plane (i.e., across the stripe width). The theory we developed suggests that the odd modes become excited in the spatially uniform microwave field of the FMR setup due to the large conductivity of metals. This promotes excitation of large-amplitude eddy currents in the sample by the incident microwave magnetic field and ultimately results in excitation of these modes. Following this theory, we found that the eddy current contribution is present only for patterned materials and when the microwave magnetic field is incident on one surface of sample surface, as it is in the case of a microstrip FMR.
Magnetic helicity evolution in a periodic domain with imposed field
Axel Brandenburg; William H. Matthaeus
In helical hydromagnetic turbulence with an imposed magnetic field (which is constant in space and time) the magnetic helicity of the field within a periodic domain is no longer an invariant of the ideal equations. Alternatively, there is a generalized magnetic helicity that is an invariant of the ideal equations. It is shown that this quantity is not gauge invariant and that it can therefore not be used in practice. Instead, the evolution equation of the magnetic helicity of the field describing the deviation from the imposed field is shown to be a useful tool. It is demonstrated that this tool can determine steady state quenching of the alpha-effect. A simple three-scale model is derived to describe the evolution of the magnetic helicity and to predict its sign as a function of the imposed field strength. The results of the model agree favorably with simulations.
Plasma-satellite interaction driven magnetic field perturbations
Saeed-ur-Rehman, E-mail: firstname.lastname@example.com [Department of Physics, University of Alberta, Edmonton, Alberta T6G 2E1 (Canada); Theoretical Physics Division, PINSTECH, Nilore Islamabad 44000 (Pakistan); Marchand, Richard, E-mail: email@example.com [Department of Physics, University of Alberta, Edmonton, Alberta T6G 2E1 (Canada)
We report the first fully kinetic quantitative estimate of magnetic field perturbations caused by the interaction of a spacecraft with space environment. Such perturbations could affect measurements of geophysical magnetic fields made with very sensitive magnetometers on-board satellites. Our approach is illustrated with a calculation of perturbed magnetic fields near the recently launched Swarm satellites. In this case, magnetic field perturbations do not exceed 20 pT, and they are below the sensitivity threshold of the on-board magnetometers. Anticipating future missions in which satellites and instruments would be subject to more intense solar UV radiation, however, it appears that magnetic field perturbations associated with satellite interaction with space environment, might approach or exceed instruments' sensitivity thresholds.
Magnetic anisotropy in a permalloy microgrid fabricated by near-field optical lithography
Li, S. P.; Lebib, A.; Peyrade, D.; Natali, M.; Chen, Y.; Lew, W. S.; Bland, J. A. C.
We report the fabrication and magnetic properties of permalloy microgrids prepared by near-field optical lithography and characterized using high-sensitivity magneto-optical Kerr effect techniques. A fourfold magnetic anisotropy induced by the grid architecture is identified. {copyright} 2001 American Institute of Physics.
Plasma expansion in the presence of a dipole magnetic field
Winske, D.; Omidi, N. [Applied Physics Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); SciberNet, Inc., Solana Beach, California 92075 (United States)
Simulations of the initial expansion of a plasma injected into a stationary magnetized background plasma in the presence of a dipole magnetic field are carried out in two dimensions with a kinetic ion, massless fluid electron (hybrid) electromagnetic code. For small values of the magnetic dipole, the injected ions have large gyroradii compared to the scale length of the dipole field and are essentially unmagnetized. As a result, these ions expand, excluding the ambient magnetic field and plasma to form a diamagnetic cavity. However, for stronger magnetic dipoles, the ratio of the gyroradii of the injected ions to the dipole field scale length is small so that they remain magnetized, and hence trapped in the dipole field, as they expand. The trapping and expansion then lead to additional plasma currents and resulting magnetic fields that not only exclude the background field but also interact with the dipole field in a more complex manner that stretches the closed dipole field lines. A criterion to distinguish between the two regimes is derived and is then briefly discussed in the context of applying the results to the plasma sail scheme for the propulsion of small spacecraft in the solar wind.
Bernal, Cristian G.; Page, Dany; Lee, William H., E-mail: email@example.com, E-mail: firstname.lastname@example.com, E-mail: email@example.com [Departamento de Astrofisica Teorica, Instituto de Astronomia, Universidad Nacional Autonoma de Mexico, Mexico, D.F. 04510 (Mexico)
We present magnetohydrodynamic numerical simulations of the late post-supernova hypercritical accretion to understand its effect on the magnetic field of the newborn neutron star. We consider as an example the case of a magnetic field loop protruding from the star's surface. The accreting matter is assumed to be non-magnetized, and, due to the high accretion rate, matter pressure dominates over magnetic pressure. We find that an accretion envelope develops very rapidly, and once it becomes convectively stable, the magnetic field is easily buried and pushed into the newly forming neutron star crust. However, for low enough accretion rates the accretion envelope remains convective for an extended period of time and only partial submergence of the magnetic field occurs due to a residual field that is maintained at the interface between the forming crust and the convective envelope. In this latter case, the outcome should be a weakly magnetized neutron star with a likely complicated field geometry. In our simulations we find the transition from total to partial submergence to occur around M-dot {approx}10 M{sub sun} yr{sup -1}. Back-diffusion of the submerged magnetic field toward the surface, and the resulting growth of the dipolar component, may result in a delayed switch-on of a pulsar on timescales of centuries to millennia.
Faraday rotation: effect of magnetic field reversals
Melrose, D B
The standard formula for the rotation measure, RM, which determines the position angle, $\\psi={\\rm RM}\\lambda^2$, due to Faraday rotation, includes contributions only from the portions of the ray path where the natural modes of the plasma are circularly polarized. In small regions of the ray path where the projection of the magnetic field on the ray path reverses sign (called QT regions) the modes are nearly linearly polarized. The neglect of QT regions in estimating RM is not well justified at frequencies below a transition frequency where mode coupling changes from strong to weak. By integrating the polarization transfer equation across a QT region in the latter limit, I estimate the additional contribution $\\Delta\\psi$ needed to correct this omission. In contrast with a result proposed by \\cite{BB10}, $\\Delta\\psi$ is small and probably unobservable. I identify a new source of circular polarization, due to mode coupling in an asymmetric QT region. I also identify a new circular-polarization-dependent correc...
Melrose, D. B. [SIfA, School of Physics, University of Sydney, NSW 2006 (Australia)
The standard formula for the rotation measure (RM), which determines the position angle, {psi} = RM{lambda}{sup 2}, due to Faraday rotation, includes contributions only from the portions of the ray path where the natural modes of the plasma are circularly polarized. In small regions of the ray path where the projection of the magnetic field on the ray path reverses sign (called QT regions) the modes are nearly linearly polarized. The neglect of QT regions in estimating RM is not well justified at frequencies below a transition frequency where mode coupling changes from strong to weak. By integrating the polarization transfer equation across a QT region in the latter limit, I estimate the additional contribution {Delta}{psi} needed to correct this omission. In contrast with a result proposed by Broderick and Blandford, {Delta}{psi} is small and probably unobservable. I identify a new source of circular polarization, due to mode coupling in an asymmetric QT region. I also identify a new circular-polarization-dependent correction to the dispersion measure at low frequencies.
Cosmic Acceleration and Anisotropic models with Magnetic field
S. K. Tripathy; K. L. Mahanta
Plane symmetric cosmological models are investigated with or without any dark energy components in the field equations. Keeping an eye on the recent observational constraints concerning the accelerating phase of expansion of the universe, the role of magnetic field is assessed. In the absence of dark energy components, magnetic field can favour an accelerating model even if we take a linear relationship between the directional Hubble parameters. In presence of dark energy components in the form of a time varying cosmological constant, the influence of magnetic field is found to be limited.
Study of HTS Insert Coils for High Field Solenoids
Lombardo, Vito; /Fermilab
Fermilab is currently working on the development of high field magnet systems for ionization cooling of muon beams. The use of high temperature superconducting materials (HTS) is being considered for these solenoids using Helium refrigeration. Several studies have been performed on insert coils made of BSCCO-2223 tapes and second generation (2G) YBCO coated conductors, which are tested at various temperatures and at external fields of up to 14 T. Critical current (I{sub c}) measurements of YBCO short samples are presented as a function of bending stress, magnetic field and field orientation with respect to the sample surface. An analytical fit of critical current data as a function of field and field orientation is also presented. Results from several single-layer and double-layer pancake coils are also discussed.
Production of large volume, strongly magnetized laser-produced plasmas by use of pulsed external magnetic fields
Albertazzi, B. [LULI, Ecole Polytechnique, CNRS, CEA, UPMC, 91128 Palaiseau (France); INRS-EMT, Varennes, Quebec J3X 1S2 (Canada); Beard, J.; Billette, J.; Portugall, O. [LNCMI, UPR 3228, CNRS-UFJ-UPS-INSA, 31400 Toulouse (France); Ciardi, A. [LERMA, Observatoire de Paris, Ecole Normale Superieure, Universite Pierre et Marie Curie, CNRS UMR 8112, Paris (France); Vinci, T.; Albrecht, J.; Chen, S. N.; Da Silva, D.; Hirardin, B.; Nakatsutsumi, M.; Romagnagni, L.; Simond, S.; Veuillot, E.; Fuchs, J. [LULI, Ecole Polytechnique, CNRS, CEA, UPMC, 91128 Palaiseau (France); Burris-Mog, T.; Dittrich, S.; Herrmannsdoerfer, T.; Kroll, F.; Nitsche, S. [Helmholtz-Zentrum Dresden-Rossendorf, P.O. Box 510119, 01314 Dresden (Germany); and others
The production of strongly magnetized laser plasmas, of interest for laboratory astrophysics and inertial confinement fusion studies, is presented. This is achieved by coupling a 16 kV pulse-power system. This is achieved by coupling a 16 kV pulse-power system, which generates a magnetic field by means of a split coil, with the ELFIE laser facility at Ecole Polytechnique. In order to influence the plasma dynamics in a significant manner, the system can generate, repetitively and without debris, high amplitude magnetic fields (40 T) in a manner compatible with a high-energy laser environment. A description of the system and preliminary results demonstrating the possibility to magnetically collimate plasma jets are given.
Distortion-free magnetic resonance imaging in the zero-field limit
Kelso, Nathan; Lee, Seung-Kyun; Bouchard, Louis-S.; Demas, Vasiliki; Muck, Michael; Pines, Alexander; Clarke, John
MRI is a powerful technique for clinical diagnosis and materials characterization. Images are acquired in a homogeneous static magnetic field much higher than the fields generated across the field of view by the spatially encoding field gradients. Without such a high field, the concomitant components of the field gradient dictated by Maxwell's equations lead to severe distortions that make imaging impossible with conventional MRI encoding. In this paper, we present a distortion-free image of a phantom acquired with a fundamentally different methodology in which the applied static field approaches zero. Our technique involves encoding with pulses of uniform and gradient field, and acquiring the magnetic field signals with a SQUID. The method can be extended to weak ambient fields, potentially enabling imaging in the Earth's field without cancellation coils or shielding. Other potential applications include quantum information processing and fundamental studies of long-range ferromagnetic interactions.
Magnetic fields, spots and weather in chemically peculiar stars
O. Kochukhov
New observational techniques and sophisticated modelling methods has led to dramatic breakthroughs in our understanding of the interplay between the surface magnetism, atomic diffusion and atmospheric dynamics in chemically peculiar stars. Magnetic Doppler images, constructed using spectropolarimetric observations of Ap stars in all four Stokes parameters, reveal the presence of small-scale field topologies. Abundance Doppler mapping has been perfected to the level where distributions of many different chemical elements can be deduced self-consistently for one star. The inferred chemical spot structures are diverse and do not always trace underlying magnetic field geometry. Moreover, horizontal chemical inhomogeneities are discovered in non-magnetic CP stars and evolving chemical spots are observed for the first time in the bright mercury-manganese star alpha And. These results show that in addition to magnetic fields, another important non-magnetic structure formation mechanism acts in CP stars.
Observation of Dirac Monopoles in a Synthetic Magnetic Field
Ray, M W; Kandel, S; M÷tt÷nen, M; Hall, D S
Magnetic monopoles --- particles that behave as isolated north or south magnetic poles --- have been the subject of speculation since the first detailed observations of magnetism several hundred years ago. Numerous theoretical investigations and hitherto unsuccessful experimental searches have followed Dirac's 1931 development of a theory of monopoles consistent with both quantum mechanics and the gauge invariance of the electromagnetic field. The existence of even a single Dirac magnetic monopole would have far-reaching physical consequences, most famously explaining the quantization of electric charge. Although analogues of magnetic monopoles have been found in exotic spin-ices and other systems, there has been no direct experimental observation of Dirac monopoles within a medium described by a quantum field, such as superfluid helium-3. Here we demonstrate the controlled creation of Dirac monopoles in the synthetic magnetic field produced by a spinor Bose-Einstein condensate. Monopoles are identified, in b...
Consistent generation of magnetic fields in axion inflation models
Fujita, Tomohiro; Tada, Yuichiro; Takeda, Naoyuki; Tashiro, Hiroyuki
There has been a growing evidence for the existence of magnetic fields in the extra-galactic regions, while the attempt to associate their origin with the inflationary epoch alone has been found extremely challenging. We therefore take into account the consistent post-inflationary evolution of the magnetic fields that are originated from vacuum fluctuations during inflation. In the model of our interest, the electromagnetic (EM) field is coupled to a pseudo-scalar inflaton $\\phi$ through the characteristic term $\\phi F\\tilde F$, breaking the conformal invariance. This interaction dynamically breaks the parity and enables a continuous production of only one of the polarization states of the EM field through tachyonic instability. The produced magnetic fields are thus helical. We find that the dominant contribution to the observed magnetic fields in this model comes from the modes that leave the horizon near the end of inflation, further enhanced by the tachyonic instability right after the end of inflation. Th...
Magnetic field in holographic superconductor with dark matter sector
Nakonieczny, L; Wysokinski, K I
Based on the analytical technique the effect of the static magnetic field on the s-wave holographic superconductor with dark matter sector of U(1)-gauge field type coupled to the Maxwell field has been examined. In the probe limit, we obtained the mean value of the condensation operator. The nature of the condensate in an external magnetic field as well as the behaviour of the critical field close to the transition temperature has been revealed. The obtained upturn of the critical field curves as a function of temperature, both in four and five spacetime dimensions, is a fingerprint of the strong coupling approach.
On Possible Light-Torsion Mixing in Background Magnetic Field
S. I. Kruglov
The interaction of the light with propagating axial torsion fields in the presence of an external magnetic field has been investigated. Axial torsion fields appearing in higher derivative quantum gravity possess two states, with spin one and zero, with different masses. The torsion field with spin-0 state is a ghost that can be removed if its mass is infinite. We investigate the possibility when the light mixes with the torsion fields resulting in the effect of vacuum birefringence and dichroism. The expressions for ellipticity and the rotation of light polarization axis depending on the coupling constant and the external magnetic field have been obtained.
Magnetic anisotropy in Fe-25Cr-12Co-1Si alloy induced by external magnetic field
Qin, Lu-Chang
Magnetic anisotropy in Fe-25Cr-12Co-1Si alloy induced by external magnetic field ZHEN Liang( )1 of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, China; 2. Department 27599-3255, USA Received 29 June 2006; accepted 15 January 2007 Abstract: Structural and magnetic
Romano, P.; Guglielmino, S. L. [INAF-Osservatorio Astrofisico di Catania, Via S. Sofia 78, I-95125 Catania (Italy); Frasca, D.; Zuccarello, F. [Dipartimento di Fisica e Astronomia-Sezione Astrofisica, Universita di Catania, Via S. Sofia 78, I-95125 Catania (Italy); Ermolli, I. [INAF-Osservatorio Astronomico di Roma, Via Frascati 33, I-00040 Monte Porzio Catone (Italy); Tritschler, A.; Reardon, K. P., E-mail: firstname.lastname@example.com [National Solar Observatory/Sacramento Peak, P.O. Box 62, Sunspot, NM 88349-0062 (United States)
We present results from the analysis of high-resolution spectropolarimetric and spectroscopic observations of the solar photosphere and chromosphere, obtained shortly before the formation of a penumbra in one of the leading polarity sunspots of NOAA active region 11490. The observations were performed at the Dunn Solar Telescope of the National Solar Observatory on 2012 May 28, using the Interferometric Bidimensional Spectrometer. The data set is comprised of a 1 hr time sequence of measurements in the Fe I 617.3 nm and Fe I 630.25 nm lines (full Stokes polarimetry) and in the Ca II 854.2 nm line (Stokes I only). We perform an inversion of the Fe I 630.25 nm Stokes profiles to derive magnetic field parameters and the line-of-sight (LOS) velocity at the photospheric level. We characterize chromospheric LOS velocities by the Doppler shift of the centroid of the Ca II 854.2 nm line. We find that, before the formation of the penumbra, an annular zone of 3''-5'' width is visible around the sunspot. In the photosphere, we find that this zone is characterized by an uncombed structure of the magnetic field although no visible penumbra has formed yet. We also find that the chromospheric LOS velocity field shows several elongated structures characterized by downflow and upflow motions in the inner and outer parts of the annular zone, respectively.
Relation between photospheric flow fields and the magnetic field distribution on the solar surface
Simon, G.W.; Title, A.M.; Topka, K.P.; Tarbell, T.D.; Shine, R.A.
Using the technique of local correlation tracking on a 28 minute time sequence of white-light images of solar granulation, the horizontal flow field on the solar surface is measured. The time series was obtained by the Solar Optical Universal Polarimeter (SOUP) on Spacelab 2 (Space Shuttle flight 51-F) and is free from atmospheric blurring and distortion. The SOUP flow fields have been compared with carefully aligned magnetograms taken over a nine hour period at the Big Bear Solar Observatory before, during, and after the SOUP images. The flow field and the magnetic field agree in considerable detail: vectors which define the flow of the white-light intensity pattern (granulation) point toward magnetic field regions, magnetic fields surround flow cells, and magnetic features move along the flow arrows. The projected locations of free particles (corks) in the measured flow field congregate at the same locations where the magnetic field is observed. 31 references.
Effects of magnetic field strength on the low frequency oscillation in Hall thrusters
Wang Chunsheng; Wei Liqiu; Ning Zhongxi; Yu Daren [Laboratory of Plasma Propulsion, Mail Box 458, Harbin Institute of Technology, Harbin 150001 (China)
In order to study the effect of magnetic field strength on low frequency oscillation in Hall thrusters, experiments were carried out with different operating parameters. Experimental results show that the effect of magnetic field strength on the low frequency oscillation changes with operating parameters. In the decline zone of magnetoampere characteristic curve, low frequency oscillation increases with the increase of magnetic field strength at low mass flow rate, while decreases with the increase of magnetic field strength at high mass flow rate. With further experiments and numerical simulations, it is found that the change of electron current at low mass flow rate and the change of ion current at high mass flow rate account for the variations of low frequency oscillation. Finally, the physical analysis is performed.
High temperature magnetic properties of SmCo5/-Fe(Co) bulk nanocomposite magnets
Liu, J. Ping
High temperature magnetic properties of SmCo5/-Fe(Co) bulk nanocomposite magnets Chuanbing Rong://apl.aip.org/about/rights_and_permissions #12;High temperature magnetic properties of SmCo5/a-Fe(Co) bulk nanocomposite magnets Chuanbing Rong,1 containing no heavy rare earths for power applications, SmCo5/Fe bulk nanocomposite magnets with enhanced
Magnetic Fields above the Surface of aSuperconductor with Internal Magnetism
Bluhm, Hendrik; /Stanford U., Phys. Dept. /SLAC, SSRl
The author presents a method for calculating the magnetic fields near a planar surface of a superconductor with a given intrinsic magnetization in the London limit. He computes solutions for various magnetic domain boundary configurations and derives relations between the spectral densities of the magnetization and the resulting field in the vacuum half space, which are useful if the magnetization can be considered as a statistical quantity and its features are too small to be resolved individually. The results are useful for analyzing and designing magnetic scanning experiments. Application to existing data from such experiments on Sr{sub 2}RuO{sub 4} show that a domain wall would have been detectable, but the magnetic field of randomly oriented small domains and small defects may have been smaller than the experimental noise level.
Magnetic Helicity and the Relaxation of Fossil Fields
Avery E. Broderick; Ramesh Narayan
In the absence of an active dynamo, purely poloidal magnetic field configurations are unstable to large-scale dynamical perturbations, and decay via reconnection on an Alfvenic timescale. Nevertheless, a number of classes of dynamo-free stars do exhibit significant, long-lived, surface magnetic fields. Numerical simulations suggest that the large-scale poloidal field in these systems is stabilized by a toroidal component of the field in the stellar interior. Using the principle of conservation of total helicity, we develop a variational principle for computing the structure of the magnetic field inside a conducting sphere surrounded by an insulating vacuum. We show that, for a fixed total helicity, the minimum energy state corresponds to a force-free configuration. We find a simple class of axisymmetric solutions, parametrized by angular and radial quantum numbers. However, these solutions have a discontinuity in the toroidal magnetic field at the stellar surface which will exert a toroidal stress on the surface of the star. We then describe two other classes of solutions, the standard spheromak solutions and ones with fixed surface magnetic fields, the latter being relevant for neutron stars with rigid crusts. We discuss the implications of our results for the structure of neutron star magnetic fields, the decay of fields, and the origin of variability and outbursts in magnetars.
Zeeman tomography of magnetic white dwarfs, I. Reconstruction of the field geometry from synthetic spectra
F. Euchner; S. Jordan; K. Beuermann; B. T. Gaensicke; F. V. Hessmann
We have computed optical Zeeman spectra of magnetic white dwarfs for field strengths between 10 and 200MG and effective temperatures between 8000 and 40000K. They form a database containing 20628 sets of flux and circular polarization spectra. A least-squares optimization code based on an evolutionary strategy can recover relatively complex magnetic field topologies from phase-resolved synthetic Zeeman spectra of rotating magnetic white dwarfs. We consider dipole and quadrupole components which are non-aligned and shifted off-centre. The model geometries include stars with a single high-field spot and with two spots separated by approx. 90 degrees. The accuracy of the recovered field structure increases with the signal-to-noise ratio of the input spectra and is significantly improved if circular polarization spectra are included in addition to flux spectra. We discuss the strategies proposed so far to unravel the field geometries of magnetic white dwarfs.
Electromagnetic Waves Reflectance of Graphene -- Magnetic Semiconductor Superlattice in Magnetic Field
Kuzmin, Dmitry A; Shavrov, Vladimir G
Electrodynamic properties of the graphene - magnetic semiconductor - graphene superlattice placed in magnetic field have been investigated theoretically in Faraday geometry with taking into account dissipation processes. Frequency and field dependences of the reflectance, transmittance and absorbtance of electromagnetic waves by such superlattice have been calculated for different numbers of periods of the structure and different sizes of the periods with using a transfer matrix method. The possibility of efficient control of electrodynamic properties of graphene - magnetic semiconductor - graphene superlattice has been shown.
Turrioni, D.; Barzi, E.; Lamm, M.; Lombardo, V.; Zlobin, A. V. [Fermi National Accelerator Laboratory Batavia, Illinois, 60510 (United States); Thieme, C. [American Superconductor (AMSC) Westborough, MA, 01581 (United States)
An experiment is in the works at Fermilab to confirm that ionization cooling is an efficient way to shrink the size of a muon beam. This would pave the way for Muon Collider machines, which however require in their last stages of acceleration very high field solenoids. The use of high temperature superconducting materials (HTS) is being considered for these magnets using Helium or higher temperature refrigeration. A sample holder was designed to perform critical current (I{sub c}) measurements of HTS conductors under externally applied magnetic fields varying from zero to 90 degree with respect to the c-axis. This was performed in an ample range of temperatures and magnetic field values. A description of the test setup and results for (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} (BSCCO-2223) tapes, and Second Generation HTS in the form of 348 superconductor are presented.
Effects of non-radial magnetic field on measuring magnetic helicity transport across solar photosphere
Song, Yongliang
It is generally believed that the evolution of magnetic helicity has a close relationship with solar activity. Before the launch of SDO, earlier studies have mostly used MDI/SOHO line of sight magnetograms and assumed that magnetic fields are radial when calculating magnetic helicity injection rate from photospheric magnetograms. However, this assumption is not necessarily true. Here we use the vector magnetograms and line of sight magnetograms, both taken by HMI/SDO, to estimate the effects of non-radial magnetic field on measuring magnetic helicity injection rate. We find that: 1) The effect of non-radial magnetic field on estimating tangential velocity is relatively small; 2) On estimating magnetic helicity injection rate, the effect of non-radial magnetic field is strong when active regions are observed near the limb and is relatively small when active regions are close to disk center; 3) The effect of non-radial magnetic field becomes minor if the amount of accumulated magnetic helicity is the only conce...
Heat pipes for use in a magnetic field
Werner, R.W.; Hoffman, M.A.
A heat pipe configuration for use in a magnetic field environment of a fusion reactor is disclosed. Heat pipes for operation in a magnetic field when liquid metal working fluids are used are optimized by flattening of the heat pipes having an unobstructed annulus which significantly reduces the adverse side region effect of the prior known cylindrically configured heat pipes. The flattened heat pipes operating in a magnetic field can remove 2--3 times the heat as a cylindrical heat pipe of the same cross sectional area. 4 figs.
Universality of critical magnetic field in holographic superconductor
D. Momeni; R. Myrzakulov
In this letter we study aspects of the holographic superconductors analytically in the presence of a constant external magnetic field. We show that the critical temperature and critical magnetic field can be calculated at nonzero temperature. We detect the Meissner effect in such superconductors. A universal relation between black hole mass $ M$ and critical magnetic field $H_c$ is proposed as $\\frac{H_c}{M^{2/3}}\\leq 0.687365$. We discuss some aspects of phase transition in terms of black hole entropy and the Bekenstein's entropy to energy upper bound.
The Stability of Magnetized Rotating Plasmas with Superthermal Fields
Martin E. Pessah; Dimitrios Psaltis
During the last decade it has become evident that the magnetorotational instability is at the heart of the enhanced angular momentum transport in weakly magnetized accretion disks around neutron stars and black holes. In this paper, we investigate the local linear stability of differentially rotating, magnetized flows and the evolution of the magnetorotational instability beyond the weak-field limit. We show that, when superthermal toroidal fields are considered, the effects of both compressibility and magnetic tension forces, which are related to the curvature of toroidal field lines, should be taken fully into account. We demonstrate that the presence of a strong toroidal component in the magnetic field plays a non-trivial role. When strong fields are considered, the strength of the toroidal magnetic field not only modifies the growth rates of the unstable modes but also determines which modes are subject to instabilities. We find that, for rotating configurations with Keplerian laws, the magnetorotational instability is stabilized at low wavenumbers for toroidal Alfven speeds exceeding the geometric mean of the sound speed and the rotational speed. We discuss the significance of our findings for the stability of cold, magnetically dominated, rotating fluids and argue that, for these systems, the curvature of toroidal field lines cannot be neglected even when short wavelength perturbations are considered. We also comment on the implications of our results for the validity of shearing box simulations in which superthermal toroidal fields are generated.
Hinode Observations of Vector Magnetic Field Change Associated with a Flare on 2006 December 13
Masahito Kubo; Takaaki Yokoyama; Yukio Katsukawa; Bruce W Lites; Saku Tsuneta; Yoshinori Suematsu; Kiyoshi Ichimoto; Toshifumi Shimizu; Shin'ichi Nagata; Theodore D Tarbell; Richard A Shine; Alan M Title; David Elmore
Continuous observations of a flare productive active region 10930 were successfully carried out with the Solar Optical Telescope onboard the Hinode spacecraft during 2007 December 6 to 19. We focus on the evolution of photospheric magnetic fields in this active region, and magnetic field properties at the site of the X3.4 class flare, using a time series of vector field maps with high spatial resolution. The X3.4 class flare occurred on 2006 December 13 at the apparent collision site between the large, opposite polarity umbrae. Elongated magnetic structures with alternatingly positive and negative polarities resulting from flux emergence appeared one day before the flare in the collision site penumbra. Subsequently, the polarity inversion line at the collision site became very complicated. The number of bright loops in Ca II H increased during the formation of these elongated magnetic structures. The flare ribbons and bright loops evolved along the polarity inversion line and one footpoint of the bright loop was located in a region having a large departure of field azimuth angle with respect to its surroundings. The SOT observations with high spatial resolution and high polarization precision reveal temporal change in fine structure of magnetic fields at the flare site: some parts of the complicated polarity inversion line then disappeared, and in those regions the azimuth angle of photospheric magnetic field changed by about 90 degrees, becoming more spatially uniform within the collision site.
A new magnetic field integral measurement system
Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)
measurements. b. Second field integral (horizontal and vertical) measurements. c. Multipole components of first field integral measurements. 2. Translation Coil a. Multipole...
Impact of Dynamic Magnetic fields on the CLIC Main Beam
Snuverink, J; Jach, C; Jeanneret, JB; Schulte, D; Stulle, F
The Compact Linear Collider (CLIC) accelerator has strong precision requirements on the position of the beam. The beam position will be sensitive to external dynamic magnetic fields (stray fields) in the nanotesla regime. The impact of these fields on the CLIC main beam has been studied by performing simulations on the lattices and tolerances have been determined. Several mitigation techniques will be discussed.
Magnetic Field Confinement in the Corona: The Role of Magnetic Helicity Accumulation
Mei Zhang; Natasha Flyer; Boon Chye Low
A loss of magnetic field confinement is believed to be the cause of coronal mass ejections (CMEs), a major form of solar activity in the corona. The mechanisms for magnetic energy storage are crucial in understanding how a field may possess enough free energy to overcome the Aly limit and open up. Previously, we have pointed out that the accumulation of magnetic helicity in the corona plays a significant role in storing magnetic energy. In this paper, we investigate another hydromagnetic consequence of magnetic-helicity accumulation. We propose a conjecture that there is an upper bound on the total magnetic helicity that a force-free field can contain. This is directly related to the hydromagnetic property that force-free fields in unbounded space have to be self-confining. Although a mathematical proof of this conjecture for any field configuration is formidable, its plausibility can be demonstrated with the properties of several families of power-law, axisymmetric force-free fields. We put forth mathematical evidence, as well as numerical, indicating that an upper bound on the magnetic helicity may exist for such fields. Thus, the accumulation of magnetic helicity in excess of this upper bound would initiate a non-equilibrium situation, resulting in a CME expulsion as a natural product of coronal evolution.
Scanning localized magnetic fields in a microfluidic device using single spin in a nano-diamond
Lim, Kangmook; Shapiro, Benjamin; Taylor, Jacob M; Waks, Edo
Nitrogen vacancy (NV) color centers in diamond have emerged as highly versatile optical emitters that exhibit room temperature spin properties. These characteristics make NV centers ideal for magnetometry which plays an important role in a broad range of chemical and biological sensing applications. The integration of NV magnetometers with microfluidic systems could enable the study of isolated chemical and biological samples in a fluid environment with high spatial resolution. Here we demonstrate a method to perform localized magnetometry with nanometer spatial precision using a single NV center in a microfluidic device. We manipulate a magnetic particle within a liquid environment using a combination of planar flow control and vertical magnetic actuation to achieve 3-dimensional manipulation. A diamond nanocrystal containing a single NV center is deposited in the microfluidic channels and acts as a local magnetic field probe. We map out the magnetic field distribution of the magnetic particle by varying its...
Scanning localized magnetic fields in a microfluidic device with a single nitrogen vacancy center
Kangmook Lim; Chad Ropp; Benjamin Shapiro; Jacob M. Taylor; Edo Waks
Nitrogen vacancy (NV) color centers in diamond have emerged as highly versatile optical emitters that exhibit room temperature spin properties. These characteristics make NV centers ideal for magnetometry, which plays an important role in chemical and biological sensing applications. The integration of NV magnetometers with microfluidic systems could enable the study of isolated chemical and biological samples in a fluid environment with high spatial resolution. Here we demonstrate a method to perform localized magnetometry with nanometer spatial precision using a single NV center in a microfluidic device. We manipulate a magnetic particle within a liquid environment using a combination of planar microfluidic flow control and vertical magnetic actuation to achieve 3-dimensional manipulation. A diamond nanocrystal containing a single NV center is deposited in the microfluidic channels and acts as a local magnetic field probe. We map out the magnetic field distribution of the magnetic particle by varying its position relative to the diamond nanocrystal and performing optically resolved electron spin resonance (ESR) measurements. We control the magnetic particle position with a 48 nm precision and attain a magnetic field sensitivity of 17.5 microTesla/Hz^1/2. These results open up the possibility for studying local magnetic properties of biological and chemical systems with high sensitivity in an integrated microfluidic platform.
Dust-Plasma Sheath in an Oblique Magnetic Field
Foroutan, G.; Mehdipour, H. [Physics Department, Faculty of Science, Sahand University of Technology, Tabriz (Iran, Islamic Republic of)
Using numerical simulations of the multi fluid equations the structure of the magnetized sheath near a plasma boundary is studied in the presence of charged dust particles. The dependence of the electron, ion, and dust densities as well as the electrostatic potential, dust charge, and ion normal velocity, on the magnetic field strength and the edge dust number density is investigated.
1 Magnetic Fields and Solar This article describesthe relationshipbetweenmagnetic
reconnection. The free magnetic energy is con- verted to thermal and non- thermal energy to power solar ares, which create thermal emissions and accel- eration of non-thermal particles. The total energy1 Magnetic Fields and Solar Flares This article describesthe relationshipbetweenmagnetic elds
November 18, 2005 Chandra Observations of Magnetic Fields and Relativistic
Schwartz, Daniel
November 18, 2005 Chandra Observations of Magnetic Fields and Relativistic Beaming in Four Quasar microwave background. If particles and magnetic #12;elds are near minimum energy density 1 Harvard CSIRO Australia Telescope National Facility, PO Box 76, Epping NSW 1710, Australia 4 Jet Propulsion
Magnetohydrodynamic turbulent cascade of coronal loop magnetic fields
Rappazzo, A. F. [Instituto de Astrofisica de Canarias, E-38200 La Laguna, Tenerife (Spain); Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109 (United States); Bartol Research Institute, Department of Physics and Astronomy, University of Delaware, Delaware 19716 (United States); Velli, M. [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109 (United States)
The Parker model for coronal heating is investigated through a high resolution simulation. An inertial range is resolved where fluctuating magnetic energy E{sub M}(k{sub perpendicular}){proportional_to}k{sub perpendicular}{sup -2.7} exceeds kinetic energy E{sub K}(k{sub perpendicular}){proportional_to}k{sub perpendicular}{sup -0.6}. Increments scale as {delta}b{sub l}{approx_equal}l{sup -0.85}and {delta}u{sub l}{approx_equal}l{sup +0.2} with velocity increasing at small scales, indicating that magnetic reconnection plays a prime role in this turbulent system. We show that spectral energy transport is akin to standard magnetohydrodynamic (MHD) turbulence even for a system of reconnecting current sheets sustained by the boundary. In this new MHD turbulent cascade, kinetic energy flows are negligible while cross-field flows are enhanced, and through a series of ''reflections'' between the two fields, cascade more than half of the total spectral energy flow.
Terahertz radiation detection by field effect transistor in magnetic field S. Boubanga-Tombet,1,a
Levelut, Claire
Terahertz radiation detection by field effect transistor in magnetic field S. Boubanga-Tombet,1,a M; accepted 30 July 2009; published online 19 August 2009 We report on terahertz radiation detection with In
The Stability of Magnetized Rotating Plasmas with Superthermal Fields
Pessah, M E
During the last decade it has become evident that the magnetorotational instability is at the heart of the enhanced angular momentum transport in weakly magnetized accretion disks around neutron stars and black holes. In this paper, we investigate the local linear stability of differentially rotating, magnetized flows and the evolution of the magnetorotational instability beyond the weak-field limit. We show that, when superthermal toroidal fields are considered, both compressibility and magnetic tension terms, related to the curvature of toroidal field lines, should be taken fully into account. We demonstrate that, contrary to the results of most previous investigations, the presence of a toroidal component in the magnetic field plays a crucial role not only in the growth rates of the unstable modes but also in determining which modes are subject to instabilities. We find that, for rotationally supported configurations, the magnetorotational instability is stabilized at low wavenumbers for toroidal Alfven sp...
Magnetic Fields and the Triaxiality of Molecular Cloud Cores
Shantanu Basu
We make the hypothesis that molecular cloud fragments are triaxial bodies with a large scale magnetic field oriented along the short axis. While consistent with theoretical expectations, this idea is supported by magnetic field strength data, which show strong evidence for flattening along the direction of the mean magnetic field. It is also consistent with early submillimeter polarization data, which show that the projected direction of the magnetic field is often slightly misaligned with the projected minor axis of a molecular cloud core, i.e., the offset angle $\\Psi$ is nonzero. We calculate distributions of $\\Psi$ for various triaxial bodies, when viewed from a random set of viewing angles. The highest viewing probability always corresponds to $\\Psi=0^{\\circ}$, but there is a finite probability of viewing all nonzero $\\Psi$, including even $\\Psi =90^{\\circ}$; the average offset typically falls in the range $10^{\\circ}-30^{\\circ}$ for triaxial bodies most likely to satisfy observational and theoretical constraints.
Low-field classroom nuclear magnetic resonance system
Zimmerman, Clarissa Lynette
The goal of this research was to develop a Low-field Classroom NMR system that will enable hands-on learning of NMR and MRI concepts in a Biological-Engineering laboratory course. A permanent magnet system, designed using ...
Ferrofluid surface and volume flows in uniform rotating magnetic fields
Elborai, Shihab M. (Shihab Mahmoud), 1977-
Ferrofluid surface and volume effects in uniform dc and rotating magnetic fields are studied. Theory and corroborating measurements are presented for meniscus shapes and resulting surface driven flows, spin-up flows, and ...
A Holographic Superconductor in an External Magnetic Field
Tameem Albash; Clifford V. Johnson
We study a system of a complex charged scalar coupled to a Reissner-Nordstrom black hole in 3+1 dimensional anti-de Sitter spacetime, neglecting back-reaction. With suitable boundary conditions, the cases of a neutral and purely electric black hole have been studied in various limits and were shown to yield key elements of superconductivity in the dual 2+1 dimensional field theory, forming a condensate below a critical temperature. By adding magnetic charge to the black hole, we immerse the superconductor into an external magnetic field. We show that a family of condensates can form and we examine their structure. For finite magnetic field, they are localized in one dimension with a profile that is exactly solvable, since it maps to the quantum harmonic oscillator. As the magnetic field increases, the condensate shrinks in size, which is reminiscent of the Meissner effect.
Primordial magnetic fields and formation of molecular hydrogen
Shiv K Sethi; Biman B. Nath; Kandaswamy Subramanian
We study the implications of primordial magnetic fields for the thermal and ionization history of the post-recombination era. In particular we compute the effects of dissipation of primordial magnetic fields owing to ambipolar diffusion and decaying turbulence in the intergalactic medium (IGM) and the collapsing halos and compute the effects of the altered thermal and ionization history on the formation of molecular hydrogen. We show that, for magnetic field strengths in the range $2 \\times 10^{-10} {\\rm G} \\la B_0 \\la 2 \\times 10^{-9} {\\rm G}$, the molecular hydrogen fraction in IGM and collapsing halo can increase by a factor 5 to 1000 over the case with no magnetic fields. We discuss the implication of the increased molecular hydrogen fraction on the radiative transfer of UV photons and the formation of first structures in the universe.
Field representation of a watt balance magnet by partial profile measurements
Li, Shisong; Zhao, Wei; Huang, Songling
Permanent magnets with high-permeability yokes have been widely used in watt balances for supplying a robust and strong magnetic field at the coil position. Subjected to the mechanical realization, only several $B_r(z)$ (radial magnetic field along the vertical direction) profiles can be measured by coils for field characterization. In this article, we present an algorithm that can construct the global magnetic field of the air gap based on $N(N\\geq1)$ additional measurements of $B_r(z)$ profiles. The proposed algorithm is realized by polynomially estimating the $B_z(r)$ function with analysis of basic relations between two magnetic components in air gap, i.e., $B_r(r,z)$ and $B_z(r,z)$, following the Maxwell's equations. The algorithm, verified by FEM simulations, can characterize the three-dimensional contribution of the magnetic field for a watt balance magnet with acceptable accuracy, which would supply basic field parameters for alignment and misalignment corrections.
Measurement of Untruncated Nuclear Spin Interactions via Zero- to Ultra-Low-Field Nuclear Magnetic Resonance
John W. Blanchard; Tobias F. Sjolander; Jonathan P. King; Micah P. Ledbetter; Emma H. Levine; Vikram S. Bajaj; Dmitry Budker; Alexander Pines
Zero- to ultra-low-field nuclear magnetic resonance (ZULF NMR) provides a new regime for the measurement of nuclear spin-spin interactions free from effects of large magnetic fields, such as truncation of terms that do not commute with the Zeeman Hamiltonian. One such interaction, the magnetic dipole-dipole coupling, is a valuable source of spatial information in NMR, though many terms are unobservable in high-field NMR, and the coupling averages to zero under isotropic molecular tumbling. Under partial alignment, this information is retained in the form of so-called residual dipolar couplings. We report zero- to ultra-low-field NMR measurements of residual dipolar couplings in acetonitrile-2-$^{13}$C aligned in stretched polyvinyl acetate gels. This represents the first investigation of dipolar couplings as a perturbation on the indirect spin-spin $J$-coupling in the absence of an applied magnetic field. As a consequence of working at zero magnetic field, we observe terms of the dipole-dipole coupling Hamiltonian that are invisible in conventional high-field NMR. This technique expands the capabilities of zero- to ultra-low-field NMR and may have applications in precision measurement of subtle physical interactions, chemical analysis, and characterization of local mesoscale structure in materials.
Persistence of magnetic field driven by relativistic electrons in a plasma
Flacco, A; Lifschitz, A; Sylla, F; Kahaly, S; Veltcheva, M; Silva, L O; Malka, V
The onset and evolution of magnetic fields in laboratory and astrophysical plasmas is determined by several mechanisms, including instabilities, dynamo effects and ultra-high energy particle flows through gas, plasma and interstellar-media. These processes are relevant over a wide range of conditions, from cosmic ray acceleration and gamma ray bursts to nuclear fusion in stars. The disparate temporal and spatial scales where each operates can be reconciled by scaling parameters that enable to recreate astrophysical conditions in the laboratory. Here we unveil a new mechanism by which the flow of ultra-energetic particles can strongly magnetize the boundary between the plasma and the non-ionized gas to magnetic fields up to 10-100 Tesla (micro Tesla in astrophysical conditions). The physics is observed from the first time-resolved large scale magnetic field measurements obtained in a laser wakefield accelerator. Particle-in-cell simulations capturing the global plasma and field dynamics over the full plasma le...
Warm inflation in the presence of magnetic fields
Gabriella Piccinelli; Angel Sanchez; Alejandro Ayala; Ana Julia Mizher
We study the effects of primordial magnetic fields on the inflationary potential in the context of a warm inflation scenario. The model, based on global supersymmetry with a new-inflation-type potential and a coupling between the inflaton and a heavy intermediate superfield, is already known to preserve the flatness required for slow-roll conditions even after including thermal contributions. Here we show that the magnetic field makes the potential even flatter, retarding the transition and rendering it smoother.
GUT Cosmic Magnetic Fields in a Warm Inflationary Universe
Arjun Berera; Thomas W. Kephart; Stuart D. Wick
Sources of magnetic fields from grand unified theories are studied in the warm inflation regime. A ferromagnetic Savvidy vacuum scenario is presented that yields observationally interesting large scale magnetic fields. As an intermediate step, a general analysis is made of defect production at the onset of warm inflation and monopole constraints are obtained. Many features of this Savvidy vacuum scenario are applicable within a supercooled inflation regime and these points are discussed.
Propellantless propulsion in magnetic fields by partially shielded current
Bergamin, L; Pinchook, A
A new device for propellantless propulsion in presence of a magnetic field is discussed. The functional principle shares some features with electrodynamic tethers. However, the tether structure is replaced by a closed wire, which is partially shielded from the magnetic field by means of a superconductor. Therefore, it does not depend on the presence of a plasma. We show that even a relatively small device can yield interesting propulsivet forces for drag compensation or for orbital transfers.
Phase-field simulation of electric-field-induced in-plane magnetic domain switching in magnetic/ferroelectric layered heterostructures
Chen, Long-Qing
). An alternative approach to engineering low electric- field-induced magnetic domain switching at room temperaPhase-field simulation of electric-field-induced in-plane magnetic domain switching in magnetic. Phys. Lett. 99, 182510 (2011) Quantum tunneling of the Bloch point in a magnetic film with strong
Collisionless Shocks -- Magnetic Field Generation and Particle Acceleration
J. Trier Frederiksen; C. B. Hededal; T. Haugboelle; A. Nordlund
We present numerical results from plasma particle simulations of collisionless shocks and ultra-relativistic counter-streaming plasmas. We demonstrate how the field-particle interactions lead to particle acceleration behind the shock-front. Further, we demonstrate how ultra relativistic counter-streaming plasmas create large scale patchy magnetic field structures and that these field structures propagate down-stream of the shock front. These results may help explain the origin of the magnetic fields and accelerated electrons responsible for afterglow synchrotron radiation from gamma ray bursts.
Confining potential from interacting magnetic and torsion fields
Patricio Gaete; Josķ A. Hela el-Neto
Adopting the gauge-invariant but path-dependent variables formalism, we study the coupling of torsion fields with photons in the presence of an external background electromagnetic. We explicitly show that, in the case of a constant electric field strength expectation value, the static potential remains Coulombic, while in the case of a constant magnetic field strength expectation value a confining potential is obtained. This result displays a marked qualitative departure from the usual coupling of axionlike particles with photons in the presence of an external magnetic field.
A holographic model for antiferromagnetic quantum phase transition induced by magnetic field
Rong-Gen Cai; Run-Qiu Yang; F. V. Kusmartsev
We propose a gravity dual of antiferromagnetic quantum phase transition (QPT) induced by magnetic field and study the criticality in the vicinity of quantum critical point (QCP). Results show the boundary critical theory is a strong coupling theory with dynamic exponent $z=2$. The hyperscaling law is violated and logarithmic corrections appear near the QCP. We compare our theoretical results with experimental data on variety of materials including low-dimensional magnet, BiCoPO$_5$ and pyrochlores, Er$_{2-2x}$Y$_{2x}$Ti$_2$O$_7$. Our model describes well the existing experiments and predicts QCP and other high field magnetic properties of these compounds.
A holographic model for antiferromagnetic quantum phase transition induced by magnetic field
Cai, Rong-Gen; Kusmartsev, F V
We propose a gravity dual of antiferromagnetic quantum phase transition (QPT) induced by magnetic field and study the criticality in the vicinity of quantum critical point (QCP). Results show the boundary critical theory is a strong coupling theory with dynamic exponent $z=2$. The hyperscaling law is violated and logarithmic corrections appear near the QCP. We compare our theoretical results with experimental data on variety of materials including low-dimensional magnet, BiCoPO$_5$ and pyrochlores, Er$_{2-2x}$Y$_{2x}$Ti$_2$O$_7$. Our model describes well the existing experiments and predicts QCP and other high field magnetic properties of these compounds.
Magnetic Fields via Polarimetry: Progress of Grain Alignment Theory
A. Lazarian
Most astrophysical systems, e.g. stellar winds, the diffuse interstellar medium, molecular clouds, are magnetized with magnetic fields that influence almost all of their properties. One of the most informative techniques of magnetic field studies is based on the use of starlight polarization and polarized emission arising from aligned dust. How reliable the interpretation of the polarization maps in terms of magnetic fields is the issue that the grain alignment theory addresses. Although grain alignment is a problem of half a century standing, recent progress achieved in the field makes us believe that we are approaching the solution of this mystery. I review basic physical processes involved in grain alignment and discuss the niches for different alignment mechanisms. I show why mechanisms that were favored for decades do not look so promising right now, while the radiative torque mechanism ignored for more than 20 years looks so attractive. I define the observational tests and outline the circumstances when grain alignment theory predicts that new yet untapped information of magnetic field structure is available through polarimetry. In particular, I touch upon mapping magnetic fields in circumstellar regions, interplanetary space and in comet comae.
Time-dependent approach to high-resolution spectroscopy and quantum dynamics of Rydberg atoms in crossed magnetic and electric fields
Tong, Xiao-Min; Chu, Shih-I
We present a general time-dependent approach for efficient and accurate treatment of high-resolution spectrocopy and quantum dynamics. The procedure is applied to an ab initio time-dependent study of three-dimensional ...
Voyager Mission, Detailed processing of weak magnetic fields; I -Constraints to the uncertainties of the calibrated magnetic field signal in the Voyager missions
Christian, Eric
which uses a coil wound around the periphery of the high gain antenna of the spacecraft. When energized/22/2009 a work possible only through the many suggestions/input form Mario H. Acu±a, vers. 12/17/2008 suggestions the coil produces Ł at the location of the sensors Ł a magnetic field whose direction and intensity
Permanent magnet design for high-speed superconducting bearings
Hull, J.R.; Uherka, K.L.; Abdoud, R.G.
A high temperature superconducting bearing including a permanent magnet rotor levitated by a high temperature superconducting structure is disclosed. The rotor preferably includes one or more concentric permanent magnet rings coupled to permanent magnet ring structures having substantially triangular and quadrangular cross-sections. Both alternating and single direction polarity magnet structures can be used in the bearing. 9 figs.
Permanent magnet design for high-speed superconducting bearings
Hull, John R. (5519 S. Bruner, Hinsdale, IL 60521); Uherka, Kenneth L. (830 Ironwood, Frankfort, IL 60423); Abdoud, Robert G. (13 Country Oaks La., Barrington Hills, IL 60010)
A high temperature superconducting bearing including a permanent magnet rotor levitated by a high temperature superconducting structure. The rotor preferably includes one or more concentric permanent magnet rings coupled to permanent magnet ring structures having substantially triangular and quadrangular cross-sections. Both alternating and single direction polarity magnet structures can be used in the bearing.
Fluorescent lamp unit with magnetic field generating means
Grossman, M.W.; George, W.A.
A fluorescent lamp unit having a magnetic field generating means for improving the performance of the fluorescent lamp is disclosed. In a preferred embodiment the fluorescent lamp comprises four longitudinally extending leg portions disposed in substantially quadrangular columnar array and joined by three generally U-shaped portions disposed in different planes. In another embodiment of the invention the magnetic field generating means comprises a plurality of permanent magnets secured together to form a single columnar structure disposed within a centrally located region defined by the shape of lamp envelope. 4 figs.
Magnetic shielding of Hall thrusters at high discharge voltages
Mikellides, Ioannis G., E-mail: firstname.lastname@example.com; Hofer, Richard R.; Katz, Ira; Goebel, Dan M. [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109 (United States)
A series of numerical simulations and experiments have been performed to assess the effectiveness of magnetic shielding in a Hall thruster operating in the discharge voltage range of 300¢700?V (I{sub sp}???2000¢2700?s) at 6?kW, and 800?V (I{sub sp} ? 3000) at 9?kW. At 6?kW, the magnetic field topology with which highly effective magnetic shielding was previously demonstrated at 300?V has been retained for all other discharge voltages; only the magnitude of the field has been changed to achieve optimum thruster performance. It is found that magnetic shielding remains highly effective for all discharge voltages studied. This is because the channel is long enough to allow hot electrons near the channel exit to cool significantly upon reaching the anode. Thus, despite the rise of the maximum electron temperature in the channel with discharge voltage, the electrons along the grazing lines of force remain cold enough to eliminate or reduce significantly parallel gradients of the plasma potential near the walls. Computed maximum erosion rates in the range of 300¢700?V are found not to exceed 10{sup ?2}?mm/kh. Such rates are ?3 orders of magnitude less than those observed in the unshielded version of the same thruster at 300?V. At 9?kW and 800?V, saturation of the magnetic circuit did not allow for precisely the same magnetic shielding topology as that employed during the 6-kW operation since this thruster was not designed to operate at this condition. Consequently, the maximum erosion rate at the inner wall is found to be ?1 order of magnitude higher (?10{sup ?1}?mm/kh) than that at 6?kW. At the outer wall, the ion energy is found to be below the sputtering yield threshold so no measurable erosion is expected.
Patterning of hydrogenated microcrystalline silicon growth by magnetic field
Fejfar, A.; Stuchlik, J.; Mates, T.; Ledinsky, M.; Honda, S.; Kocka, J. [Institute of Physics, Academy of Sciences of the Czech Republic, Cukrovarnicka 10, 162 53 Prague 6 (Czech Republic)
A way of influencing growth of silicon films by magnetic field is demonstrated. Permanent magnet(s) placed under the substrate influenced the discharge in a mixture of silane and hydrogen and led to formation of microcrystalline regions in otherwise amorphous film. The pattern of microcrystalline regions varied with the orientation of the magnetic field. Microscopic study by atomic force microscopy and by micro-Raman spectroscopy revealed that the microcrystalline regions resulted from a higher density of crystalline grain nuclei, increased at the locations where the magnetron effect could be expected. This phenomenon could be used to study the transition between amorphous and microcrystalline growth. Moreover, we suggest it as a kind of 'magnetic lithography' for the preparation of predefined microcrystalline patterns in otherwise amorphous silicon films.
Localized Axion Photon States in a Strong Magnetic Field
E. I. Guendelman
We consider the axion field and electromagnetic waves with rapid time dependence, coupled to a strong time independent, asymptotically approaching a constant at infinity "mean" magnetic field, which takes into account the back reaction from the axion field and electromagnetic waves with rapid time dependence in a time averaged way. The direction of the self consistent mean field is orthogonal to the common direction of propagation of the axion and electromagnetic waves with rapid time dependence and parallel to the polarization of these electromagnetic waves. Then, there is an effective U(1) symmetry mixing axions and photons. Using the natural complex variables that this U(1) symmetry suggests we find localized planar soliton solutions. These solutions appear to be stable since they produce a different magnetic flux than the state with only a constant magnetic field, which we take as our "ground state". The solitons also have non trivial U(1) charge defined before, different from the uncharged vacuum.
Extragalactic Magnetic Field and the Highest Energy Cosmic Rays
Sangjin Lee; Angela Olinto; Guenter Sigl
The strength and spectrum of the extragalactic magnetic field are still unknown. Its measurement would help answer the question of whether galactic fields are purely a primordial relic or were dynamically enhanced from a much smaller cosmological seed field. In this letter, we show that the composition, spectrum, and directional distribution of extragalactic ultrahigh energy cosmic rays with energies above $\\simeq 10^{18}\\ev$ can probe the large scale component of the extragalactic magnetic field below the present observational upper limit of $10^{-9}$ Gauss. Cosmic ray detectors under construction or currently in the proposal stage should be able to test the existence of the extragalactic magnetic fields on scales of a few to tens of Mpc and strengths in the range $\\simeq 10^{-10} - 10^{-9}$ Gauss.
Nematic order of model goethite nanorods in a magnetic field
H. H. Wensink; G. J. Vroege
We explore the nematic order of model goethite nanorods in an external magnetic field within Onsager-Parsons density functional theory. The goethite rods are represented by monodisperse, charged spherocylinders with a permanent magnetic moment along the rod main axis, forcing the particles to align parallel to the magnetic field at low field strength. The intrinsic diamagnetic susceptibility anisometry of the rods is negative which leads to a preferred perpendicular orientation at higher field strength. It is shown that these counteracting effects may give rise to intricate phase behavior, including a pronounced stability of biaxial nematic order and the presence of reentrant phase transitions and demixing phenomena. The effect of the applied field on the nematic-to-smectic transition will also be addressed.
Ciovati, Gianluigi [JLAB
The performance of SRF cavities made of bulk Nb at high fields (peak surface magnetic field greater than about 90 mT) is characterized by exponentially increasing RF losses (high-field Q-slope), in the absence of field emission, which are often mitigated by a low temperature (100-140 ░C, 12-48h) baking. In this contribution, recent experimental results and phenomenological models to explain this effect will be briefly reviewed. New experimental results on the high-field Q-slope will be presented for cavities that had been heat treated at high temperature in the presence of a small partial pressure of nitrogen. Improvement of the cavity performances have been obtained, while surface analysis measurements on Nb samples treated with the cavities revealed significantly lower hydrogen concentration than for samples that followed standard cavity treatments.
Chapman, Nicholas L.; Matthews, Tristan G.; Novak, Giles [Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA) and Department of Physics and Astronomy, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208 (United States); Davidson, Jacqueline A. [School of Physics, University of Western Australia, 35 Stirling Hwy, Crawley, WA 6009 (Australia); Goldsmith, Paul F. [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, MS 264-782, Pasadena, CA 91109 (United States); Houde, Martin [Department of Physics and Astronomy, University of Western Ontario, London, ON (Canada); Kwon, Woojin; Looney, Leslie W. [Department of Astronomy, University of Illinois, 1002 West Green Street, Urbana, IL 61801 (United States); Li Zhiyun [Astronomy Department, University of Virginia, Charlottesville, VA 22904 (United States); Matthews, Brenda [Herzberg Institute of Astrophysics, National Research Council of Canada, 5071 West Saanich Road, Victoria, BC V9E 2E7 (Canada); Peng Ruisheng [Caltech Submillimeter Observatory, 111 Nowelo Street, Hilo, HI 96720 (United States); Vaillancourt, John E. [SOFIA Science Center, Universities Space Research Association, NASA Ames Research Center, MS 232-11, Moffett Field, CA 94035-0001 (United States); Volgenau, Nikolaus H. [California Institute of Technology, Owens Valley Radio Observatory, Big Pine, CA 93513 (United States)
We present 350 {mu}m polarization observations of four low-mass cores containing Class 0 protostars: L483, L1157, L1448-IRS2, and Serp-FIR1. This is the second paper in a larger survey aimed at testing magnetically regulated models for core-collapse. One key prediction of these models is that the mean magnetic field in a core should be aligned with the symmetry axis (minor axis) of the flattened young stellar object inner envelope (aka pseudodisk). Furthermore, the field should exhibit a pinched or hourglass-shaped morphology as gravity drags the field inward toward the central protostar. We combine our results for the four cores with results for three similar cores that were published in the first paper from our survey. An analysis of the 350 {mu}m polarization data for the seven cores yields evidence of a positive correlation between mean field direction and pseudodisk symmetry axis. Our rough estimate for the probability of obtaining by pure chance a correlation as strong as the one we found is about 5%. In addition, we combine together data for multiple cores to create a source-averaged magnetic field map having improved signal-to-noise ratio, and this map shows good agreement between mean field direction and pseudodisk axis (they are within 15 Degree-Sign ). We also see hints of a magnetic pinch in the source-averaged map. We conclude that core-scale magnetic fields appear to be strong enough to guide gas infall, as predicted by the magnetically regulated models. Finally, we find evidence of a positive correlation between core magnetic field direction and bipolar outflow axis.
Magnetic field-induced phase transformation in NiMnCoIn magnetic shape memory alloys - a new actuation mechanism with large work output.
Karaca, H. E.; Karaman, I.; Basaran, B.; Ren, Y.; Chumlyakov, Y. I.; Maier, H. J.; X-Ray Science Division; Texsas A& M Univ.; Univ. of Kentucky; Siberian Physical-Technical Inst.; Univ. of Paderborn
Magnetic shape memory alloys (MSMAs) have recently been developed into a new class of functional materials that are capable of magnetic-field-induced actuation, mechanical sensing, magnetic refrigeration, and energy harvesting. In the present work, the magnetic field-induced martensitic phase transformation (FIPT) in Ni{sub 45}Mn{sub 36.5}Co{sub 5}In{sub 13.5} MSMA single crystals is characterized as a new actuation mechanism with potential to result in ultra-high actuation work outputs. The effects of the applied magnetic field on the transformation temperatures, magnetization, and superelastic response are investigated. The magnetic work output of NiMnCoIn alloys is determined to be more than 1 MJ m{sup -3} per Tesla, which is one order of magnitude higher than that of the most well-known MSMAs, i.e., NiMnGa alloys. In addition, the work output of NiMnCoIn alloys is orientation independent, potentially surpassing the need for single crystals, and not limited by a saturation magnetic field, as opposed to NiMnGa MSMAs. Experimental and theoretical transformation strains and magnetostress levels are determined as a function of crystal orientation. It is found that [111]-oriented crystals can demonstrate a magnetostress level of 140 MPa T{sup -1} with 1.2% axial strain under compression. These field-induced stress and strain levels are significantly higher than those from existing piezoelectric and magnetostrictive actuators. A thermodynamical framework is introduced to comprehend the magnetic energy contributions during FIPT. The present work reveals that the magnetic FIPT mechanism is promising for magnetic actuation applications and provides new opportunities for applications requiring high actuation work-outputs with relatively large actuation frequencies. One potential issue is the requirement for relatively high critical magnetic fields and field intervals (1.5-3 T) for the onset of FIPT and for reversible FIPT, respectively.
Cyclic behavior of solar inter-network magnetic field
Jin, Chunlan
Solar inter-network magnetic field is the weakest component of solar magnetism, but contributes most of the solar surface magnetic flux. The study on its origin has been constrained by the inadequate tempo-spatial resolution and sensitivity of polarization observations. With dramatic advances in spatial resolution and detective sensitivity, solar spectro-polarimetry provided by the Solar Optical Telescope aboard Hinode in an interval from solar minimum to maximum of cycle 24 opens an unprecedented opportunity to study the cyclic behavior of solar inter-network magnetic field. More than 1000 Hinode magnetograms observed from 2007 January to 2014 August are selected in the study. It has been found that there is a very slight correlation between sunspot number and magnetic field at the inter-network flux spectrum. From solar minimum to maximum of cycle 24, the flux density of solar inter-network field is invariant, which is 10$\\pm1$ G. The observations suggest that the inter-network magnetic field does not arise...
Magnetic Propulsion of Intense Lithium Streams in a Tokamak Magnetic Field
Leonid E. Zakharov
The paper gives the theory of magnetic propulsion of liquid lithium streams and their stability in tokamaks. In the approximation of a thin flowing layer the MHD equations are reduced to one integro-differential equation which takes into account the propulsion effect, viscosity and the drag force due to magnetic pumping and other interactions with the magnetic field. A criterion is obtained for the stabilization of the ''sausage'' instability of the streams by centrifugal force.
Quantum field theory in a magnetic field: From quantum chromodynamics to graphene and Dirac semimetals
Miransky, Vladimir A
A range of quantum field theoretical phenomena driven by external magnetic fields and their applications in relativistic systems and quasirelativistic condensed matter ones, such as graphene and Dirac/Weyl semimetals, are reviewed. We start by introducing the underlying physics of the magnetic catalysis. The dimensional reduction of the low-energy dynamics of relativistic fermions in an external magnetic field is explained and its role in catalyzing spontaneous symmetry breaking is emphasized. The general theoretical consideration is supplemented by the analysis of the magnetic catalysis in quantum electrodynamics, chromodynamics and quasirelativistic models relevant for condensed matter physics. By generalizing the ideas of the magnetic catalysis to the case of nonzero density and temperature, we argue that other interesting phenomena take place. The chiral magnetic and chiral separation effects are perhaps the most interesting among them. In addition to the general discussion of the physics underlying chira...
Locked modes and magnetic field errors in MST
Almagri, A.F.; Assadi, S.; Prager, S.C.; Sarff, J.S.; Kerst, D.W.
In the MST reversed field pinch magnetic oscillations become stationary (locked) in the lab frame as a result of a process involving interactions between the modes, sawteeth, and field errors. Several helical modes become phase locked to each other to form a rotating localized disturbance, the disturbance locks to an impulsive field error generated at a sawtooth crash, the error fields grow monotonically after locking (perhaps due to an unstable interaction between the modes and field error), and over the tens of milliseconds of growth confinement degrades and the discharge eventually terminates. Field error control has been partially successful in eliminating locking.
Color-Superconducting Gap in the Presence of a Magnetic Field
Efrain J. Ferrer; Vivian de la Incera; Cristina Manuel
We explore the effects of an external magnetic field in the structure and magnitude of the diquark condensate in a three massless quark flavor color superconductor. It is shown that the long-range component $\\widetilde{B}$ of the external magnetic field that penetrates the color-flavor locked (CFL) phase modifies its gap structure, producing a new phase of lower symmetry. Our analysis is performed within an NJL effective field theory with four-fermion interactions, inspired by one-gluon exchange. Using Ritus' method, we compute the quark propagators in the presence of a background magnetic field, and derive the gap equations for arbitrary values of the field. An analytical solution is found for strong magnetic fields. A main outcome of our study is that the $\\widetilde{B}$ field tends to strengthen the gaps that get contributions from pairs of $\\widetilde{Q}$-charged quarks. These gaps are enhanced through the field-dependent density of states of the $\\widetilde{Q}$-charged quarks on the Fermi surface. Our considerations are relevant for the study of highly magnetized compact stars.
Brushed permanent magnet DC MLC motor operation in an external magnetic field
Yun, J.; St Aubin, J.; Rathee, S.; Fallone, B. G. [Department of Physics, University of Alberta, 11322-89 Avenue, Edmonton, Alberta T6G 2G7 (Canada) and Department of Oncology, Medical Physics Division, University of Alberta, 11560 University Avenue, Edmonton, Alberta T6G 1Z2 (Canada); Department of Medical Physics, Cross Cancer Institute, 11560 University Avenue, Edmonton, Alberta T6G 1Z2 (Canada) and Department of Oncology, Medical Physics Division, University of Alberta, 11560 University Avenue, Edmonton, Alberta T6G 1Z2 (Canada); Department of Physics, University of Alberta, 11322-89 Avenue, Edmonton, Alberta T6G 2G7 (Canada); Department of Medical Physics, Cross Cancer Institute, 11560 University Avenue, Edmonton, Alberta T6G 1Z2 (Canada) and Department of Oncology, Medical Physics Division, University of Alberta, 11560 University Avenue, Edmonton, Alberta T6G 1Z2 (Canada)
Purpose: Linac-MR systems for real-time image-guided radiotherapy will utilize the multileaf collimators (MLCs) to perform conformal radiotherapy and tumor tracking. The MLCs would be exposed to the external fringe magnetic fields of the linac-MR hybrid systems. Therefore, an experimental investigation of the effect of an external magnetic field on the brushed permanent magnet DC motors used in some MLC systems was performed. Methods: The changes in motor speed and current were measured for varying external magnetic field strengths up to 2000 G generated by an EEV electromagnet. These changes in motor characteristics were measured for three orientations of the motor in the external magnetic field, mimicking changes in motor orientations due to installation and/or collimator rotations. In addition, the functionality of the associated magnetic motor encoder was tested. The tested motors are used with the Varian 120 leaf Millennium MLC (Maxon Motor half leaf and full leaf motors) and the Varian 52 leaf MKII MLC (MicroMo Electronics leaf motor) including a carriage motor (MicroMo Electronics). Results: In most cases, the magnetic encoder of the motors failed prior to any damage to the gearbox or the permanent magnet motor itself. This sets an upper limit of the external magnetic field strength on the motor function. The measured limits of the external magnetic fields were found to vary by the motor type. The leaf motor used with a Varian 52 leaf MKII MLC system tolerated up to 450{+-}10 G. The carriage motor tolerated up to 2000{+-}10 G field. The motors used with the Varian 120 leaf Millennium MLC system were found to tolerate a maximum of 600{+-}10 G. Conclusions: The current Varian MLC system motors can be used for real-time image-guided radiotherapy coupled to a linac-MR system, provided the fringe magnetic fields at their locations are below the determined tolerance levels. With the fringe magnetic fields of linac-MR systems expected to be larger than the tolerance levels determined, some form of magnetic shielding would be required.
Magnetic field diffusion modeling of a small enclosed firing system
Warne, L.K.; Merewether, K.O.
Intense magnetic fields exist in the immediate vicinity of a lightning strike (and near power lines). Conducting barriers increase the rise time (and thus decrease the rise rate) interior to the barrier, but typically do not prevent penetration of the magnetic field, since the lightning current fall time may be larger than the barrier diffusion time. Thus, substantial energy is present in the interior field, although the degradation of rise rate makes it more difficult to couple into electrical circuits. This report assesses the threat posed by the diffusive magnetic field to interior components and wire loops (where voltages are induced). Analytical and numerical bounding analyses are carried out on a pill box shaped conducting barrier to develop estimates for the worst case magnetic field threats inside the system. Worst case induced voltages and energies are estimated and compared with threshold charge voltages and energies on the output capacitor of the system. Variability of these quantities with respect to design parameters are indicated. The interior magnetic field and induced voltage estimates given in this report can be used as excitations for more detailed interior and component models.
Photon and Axion Splitting in an Inhomogeneous Magnetic Field
E. I. Guendelman
The axion photon system in an external magnetic field, when the direction of propagation of axions and photons is orthogonal to the direction of the external magnetic field, displays a continuous axion-photon duality symmetry in the limit the axion mass is neglected. The conservation law that follow in this effective 2+1 dimensional theory from this symmetry is obtained. The magnetic field interaction is seen to be equivalent to first order to the interaction of a complex charged field with an external electric potential, where this ficticious "electric potential" is proportional to the external magnetic field. This allows one to solve for the scattering amplitudes using already known scalar QED results. From the scalar QED analog the axion and the photon are symmetric and antisymmetric combinations of particle and antiparticle. If one considers therefore scattering experiments in which the two spatial dimensions of the effective theory are involved non trivially, one observes that both particle and antiparticle components of photons and axions are preferentially scattered in different directions, thus producing the splitting or decomposition of the photon and axion into their particle and antiparticle components in an inhomogeneous magnetic field. This observable in principle effect is of first order in the axion photon coupling, unlike the "light shining through a wall phenomena ", which is second order.
Properties of an axially periodic magnetic field in a betatron
Zvontsov, A.A.; Filinova, V.A.; Chakhlov, V.L.
It is shown by solving an equation for the vector potential A (r, z) of the magnetic field that under appropriate conditions the focusing properties of a betatron magnetic field are periodic with respect to the z coordinate. Under these conditions there may be several equilibrium orbits lying in parallel planes z = 0, z = z/sub 01/ xxx, z = mz/sub 01/ in the accelerator. An equation is derived for the distance z/sub 01/ between the equilibrium orbit planes for a given orbit radius r/sub 0/ and field decay exponent n/sub 0/. The operation of such accelerators is described.
Primordial Magnetic Fields from the Post-Inflationary Universe
Takeshi Kobayashi
We explore cosmological magnetogenesis in the post-inflationary universe, when the inflaton oscillates around its potential minimum and the universe is effectively dominated by cold matter. During this epoch prior to reheating, large-scale magnetic fields can be significantly produced by the cosmological background. By considering magnetogenesis both during and after inflation, we demonstrate that magnetic fields stronger than 10^{-15} G can be generated on Mpc scales without having strong couplings in the theory, or producing too large electric fields that would dominate the universe.
Primordial Magnetic Fields from the Post-Inflationary Universe
Kobayashi, Takeshi
We explore cosmological magnetogenesis in the post-inflationary universe, when the inflaton oscillates around its potential minimum and the universe is effectively dominated by cold matter. During this epoch prior to reheating, large-scale magnetic fields can be significantly produced by the cosmological background. By considering magnetogenesis both during and after inflation, we demonstrate that magnetic fields stronger than 10^{-15} G can be generated on Mpc scales without having strong couplings in the theory, or producing too large electric fields that would dominate the universe.
Treating Cancer with Strong Magnetic Fields and Ultrasound
Dr. Friedwardt Winterberg
It is proposed to treat cancer by the combination of a strong magnetic field with intense ultrasound. At the low electrical conductivity of tissue the magnetic field is not frozen into the tissue, and oscillates against the tissue which is brought into rapid oscillation by the ultrasound. As a result, a rapidly oscillating electric field is induced in the tissue, strong enough to disrupt cancer cell replication. Unlike radio frequency waves, which have been proposed for this purpose, ultrasound can be easily focused onto the regions to be treated. This method has the potential for the complete eradication of the tumor.
Simple basis for hydrogenic atoms in magnetic fields
Gallas, J.A.C.
A field-dependent hydrogenic basis is used to obtain the evolution of the energy spectrum of atoms in strong (approx.10/sup 8/ G) and uniform magnetic fields. The basis allows results to be derived analytically. Numerical values for the first 13 excited states of hydrogen are found to be in very good agreement with much more elaborate calculations of Smith et al. and of Brandi. In addition, the possibility of having a remnant type of degeneracy in the presence of the magnetic field is investigated.
Magnetic Fields in Quantum Degenerate Systems and in Vacuum
H. Perez Rojas; E. Rodriguez Querts
We consider self-magnetization of charged and neutral vector bosons bearing a magnetic moment in a gas and in vacuum. For charged vector bosons (W bosons) a divergence of the magnetization in both the medium and the electroweak vacuum occurs for the critical field B=B_{wc}=m_{w}^{2}/e. For B>B_{wc} the system is unstable. This behavior suggests the occurrence of a phase transition at B=B_{c}, where the field is self-consistently maintained. This mechanism actually prevents $B$ from reaching the critical value B_{c}. For virtual neutral vector bosons bearing an anomalous magnetic moment, the ground state has a similar behavior for B=B_{nbc}=m_{nb}^{2}/q . The magnetization in the medium is associated to a Bose-Einstein condensate and we conjecture a similar condensate occurs also in the case of vacuum. The model is applied to virtual electron-positron pairs bosonization in a magnetic field B \\sim B_{pc}\\lesssim 2m_{e}^{2}/e, where m_e is the electron mass. This would lead also to vacuum self-magnetization in QED, where in both cases the symmetry breaking is due to a condensate of quasi-massless particles.
Equilibrium and stability studies of plasmas confined in a dipole magnetic field using magnetic measurements
Karim, Ishtak
The Levitated Dipole Experiment (LDX) is the first experiment of its kind to use a levitated current ring to confine a plasma in a dipole magnetic field. Unlike most other confinement devices, plasma compressibility ...
He I vector magnetic field maps of a sunspot and its superpenumbral fine-structure
Schad, T A; Lin, H; Tritschler, A
Advanced inversions of high-resolution spectropolarimetric observations of the He I triplet at 1083 nm are used to generate unique maps of the chromospheric magnetic field vector across a sunspot and its superpenumbral canopy. The observations were acquired by the Facility Infrared Spectropolarimeter (FIRS) at the Dunn Solar Telescope (DST) on 29 January 2012. Multiple atmospheric models are employed in the inversions, as superpenumbral Stokes profiles are dominated by atomic-level polarization while sunspot profiles are Zeeman-dominated but also exhibit signatures perhaps induced by symmetry breaking effects of the radiation field incident on the chromospheric material. We derive the equilibrium magnetic structure of a sunspot in the chromosphere, and further show that the superpenumbral magnetic field does not appear finely structured, unlike the observed intensity structure. This suggests fibrils are not concentrations of magnetic flux but rather distinguished by individualized thermalization. We also dire...
740 IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 12, NO. 1, MARCH 2002 High-Resolution Nuclear Magnetic Resonance
Wider, Gerhard
740 IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 12, NO. 1, MARCH 2002 High research depend on high- field superconducting magnets with outstanding homogeneity and excellent long term, superconducting magnets, TROSY. I. INTRODUCTION IN THE half century since its discovery, nuclear magnetic
Magnetic field re-arrangement after prominence eruption
Kopp, R.A.; Poletto, G.
It has long been known that magnetic reconnection plays a fundamental role in a variety of solar events. Although mainly invoked in flare problems, large-scale loops interconnecting active regions, evolving coronal hole boundaries, the solar magnetic cycle itself, provide different evidence of phenomena which involve magnetic reconnection. A further example might be given by the magnetic field rearrangement which occurs after the eruption of a prominence. Since most often a prominence reforms after its disappearance and may be observed at about the same position it occupied before erupting, the magnetic field has to undergo a temporary disruption to relax back, via reconnection, to a configuration similar to the previous one. The above sequence of events is best observable in the case of two-ribbon (2-R) flares but most probably is associated with all filament eruptions. Even if the explanation of the magnetic field rearrangement after 2-R flares in terms of reconnection is generally accepted, the lack of a three-dimensional model capable of describing the field reconfiguration, has prevented, up to now, a thorough analysis of its topology as traced by H..cap alpha../x-ray loops. The purpose of the present work is to present a numerical technique which enables one to predict and visualize the reconnected configuration, at any time t, and therefore allows one to make a significant comparison of observations and model predictions throughout the whole process. 5 refs., 3 figs.
Passive Superconducting Flux Conservers for Rotating-Magnetic-Field-Driven Field-Reversed Configurations
E. Oz, C.E. Myers, M.R. Edwards, B. Berlinger, A. Brooks, and S.A. Cohen
The Princeton Field-Reversed Configuration (PFRC) experiment employs an odd-parity rotating magnetic field (RMFo) current drive and plasma heating system to form and sustain high-? plasmas. For radial confinement, an array of coaxial, internal, passive, flux-conserving (FC) rings applies magnetic pressure to the plasma while still allowing radio-frequency RMFo from external coils to reach the plasma. The 3 ms pulse duration of the present experiment is limited by the skin time (?fc) of its room-temperature copper FC rings. To explore plasma phenomena with longer characteristic times, the pulse duration of the next-generation PFRC-2 device will exceed 100 ms, necessitating FC rings with (?fc > 300 ms. In this paper we review the physics of internal, discrete, passive FCs and describe the evolution of the PFRC's FC array. We then detail new experiments that have produced higher performance FC rings that contain embedded high-temperature superconducting (HTS) tapes. Several HTS tape winding configurations have been studied and a wide range of extended skin times, from 0.4 s to over 103 s, has been achieved. The new FC rings must carry up to 3 kA of current to balance the expected PFRC-2 plasma pressure, so the dependence of the HTS-FC critical current on the winding configuration and temperature was also studied. From these experiments, the key HTS-FC design considerations have been identified and HTS-FC rings with the desired performance characteristics have been produced.
Magnetic nanowire based high resolution magnetic force microscope probes
Qin, Lu-Chang
-resolution magnetic force microscope probes using preformed magnetic nanowires. Nickel and cobalt nanowires produced by electrodeposition were directly assembled onto the tip of a commercial atomic force microscope cantilever
Tail-ion transport and Knudsen layer formation in the presence of magnetic fields
Schmit, P. F. [Sandia National Laboratories, MS 1186, P.O. Box 5800, Albuquerque, New Mexico 87185-1186 (United States)] [Sandia National Laboratories, MS 1186, P.O. Box 5800, Albuquerque, New Mexico 87185-1186 (United States); Molvig, Kim; Nakhleh, C. W. [Los Alamos National Laboratory, MS B259, P.O. Box 1663, Los Alamos, New Mexico 87545 (United States)] [Los Alamos National Laboratory, MS B259, P.O. Box 1663, Los Alamos, New Mexico 87545 (United States)
Knudsen layer losses of tail fuel ions could reduce significantly the fusion reactivity of highly compressed cylindrical and spherical targets in inertial confinement fusion (ICF). With the class of magnetized ICF targets in mind, the effect of embedded magnetic fields on Knudsen layer formation is investigated for the first time. The modified energy scaling of ion diffusivity in magnetized hot spots is found to suppress the preferential losses of tail-ions perpendicular to the magnetic field lines to a degree that the tail distribution can be at least partially, if not fully, restored. Two simple threshold conditions are identified leading to the restoration of fusion reactivity in magnetized hot spots. A kinetic equation for tail-ion transport in the presence of a magnetic field is derived, and solutions to the equation are obtained numerically in simulations. Numerical results confirm the validity of the threshold conditions for restored reactivity and identify two different asymptotic regimes of the fusion fuel. While Knudsen layer formation is shown to be suppressed entirely in strongly magnetized cylindrical hot spot cavities, uniformly magnetized spherical cavities demonstrate remnant, albeit reduced, levels of tail-ion depletion.
Memorandum Approval of a Permanenet Variance Regarding Static Magnetic Fields at Brookhaven National Laboratory (Variance 1021)
Broader source: Energy.gov [DOE]
Approval of a Permanenet Variance Regarding Static Magnetic Fields at Brookhaven National Laboratory (Variance 1021)
Proposal for study of $\\pi^{-}$ nucleur collisions in nuclear emulsion exposed in a pulsed magnetic field
CERN. Geneva. SPS Experiments Committee
Proposal for study of $\\pi^{-}$ nucleur collisions in nuclear emulsion exposed in a pulsed magnetic field
High performance magnet power supply optimization
Jackson, L.T.
The power supply system for the joint LBL--SLAC proposed accelerator PEP provides the opportunity to take a fresh look at the current techniques employed for controlling large amounts of dc power and the possibility of using a new one. A basic requirement of +- 100 ppM regulation is placed on the guide field of the bending magnets and quadrupoles placed around the 2200 meter circumference of the accelerator. The optimization questions to be answered by this paper are threefold: Can a firing circuit be designed to reduce the combined effects of the harmonics and line voltage combined effects of the harmonics and line voltage unbalance to less than 100 ppM in the magnet field. Given the ambiguity of the previous statement, is the addition of a transistor bank to a nominal SCR controlled system the way to go or should one opt for an SCR chopper system running at 1 KHz where multiple supplies are fed from one large dc bus and the cost--performance evaluation of the three possible systems.
High performance magnetic bearing systems using high temperature superconductors
Abboud, Robert G. (Barrington Hills, IL)
A magnetic bearing apparatus and a method for providing at least one stabilizing force in a magnetic bearing structure with a superconducting magnetic assembly and a magnetic assembly, by providing a superconducting magnetic member in the superconducting magnetic assembly with a plurality of domains and arranging said superconducting magnetic member such that at least one domain has a domain C-axis vector alignment angularly disposed relative to a reference axis of the magnetic member in the magnetic assembly.
High performance magnetic bearing systems using high temperature superconductors
Abboud, R.G.
Disclosed are a magnetic bearing apparatus and a method for providing at least one stabilizing force in a magnetic bearing structure with a superconducting magnetic assembly and a magnetic assembly, by providing a superconducting magnetic member in the superconducting magnetic assembly with a plurality of domains and arranging said superconducting magnetic member such that at least one domain has a domain C-axis vector alignment angularly disposed relative to a reference axis of the magnetic member in the magnetic assembly. 7 figs.
Potts models with magnetic field: arithmetic, geometry, and computation
Shival Dasu; Matilde Marcolli
We give a sheaf theoretic interpretation of Potts models with external magnetic field, in terms of constructible sheaves and their Euler characteristics. We show that the polynomial countability question for the hypersurfaces defined by the vanishing of the partition function is affected by changes in the magnetic field: elementary examples suffice to see non-polynomially countable cases that become polynomially countable after a perturbation of the magnetic field. The same recursive formula for the Grothendieck classes, under edge-doubling operations, holds as in the case without magnetic field, but the closed formulae for specific examples like banana graphs differ in the presence of magnetic field. We give examples of computation of the Euler characteristic with compact support, for the set of real zeros, and find a similar exponential growth with the size of the graph. This can be viewed as a measure of topological and algorithmic complexity. We also consider the computational complexity question for evaluations of the polynomial, and show both tractable and NP-hard examples, using dynamic programming.
Influence of thermal agitation on the electric field induced precessional magnetization reversal with perpendicular easy axis
Cheng, Hongguang, E-mail: email@example.com; Deng, Ning [Institute of Microelectronics, Tsinghua University, Beijing 100084 (China)] [Institute of Microelectronics, Tsinghua University, Beijing 100084 (China)
We investigated the influence of thermal agitation on the electric field induced precessional magnetization switching probability with perpendicular easy axis by solving the Fokker-Planck equation numerically with finite difference method. The calculated results show that the thermal agitation during the reversal process crucially influences the switching probability. The switching probability can be achieved is only determined by the thermal stability factor ? of the free layer, it is independent on the device dimension, which is important for the high density device application. Ultra-low error rate down to the order of 10{sup ?9} can be achieved for the device of thermal stability factor ? of 40. Low damping factor ? material should be used for the free layer for high reliability device applications. These results exhibit potential of electric field induced precessional magnetization switching with perpendicular easy axis for ultra-low power, high speed and high density magnetic random access memory (MRAM) applications.
The Cost of Superconducting Magnets as a Function of Stored Energy and Design Magnetic Induction Times the Field Volume
Green, Mike; Green, M.A.; Strauss, B.P.
By various theorems one can relate the capital cost of superconducting magnets to the magnetic energy stored within that magnet. This is particularly true for magnet where the cost is dominated by the structure needed to carry the magnetic forces. One can also relate the cost of the magnet to the product of the magnetic induction and the field volume. The relationship used to estimate the cost the magnet is a function of the type of magnet it is. This paper updates the cost functions given in two papers that were published in the early 1990 s. The costs (escalated to 2007 dollars) of large numbers of LTS magnets are plotted against stored energy and magnetic field time field volume. Escalated costs for magnets built since the early 1990 s are added to the plots.
Magnetic Backgrounds and Noncommutative Field Theory
Richard J. Szabo
This paper is a rudimentary introduction, geared at non-specialists, to how noncommutative field theories arise in physics and their applications to string theory, particle physics and condensed matter systems.
Ewertowski, Bartek; Basu, Shantanu, E-mail: email@example.com [Department of Physics and Astronomy, Western University, London, Ontario N6A 3K7 (Canada)] [Department of Physics and Astronomy, Western University, London, Ontario N6A 3K7 (Canada)
Starting with a mathematical boundary value problem for the magnetic vector potential in an axisymmetric cylindrical coordinate system, we derive a general solution for any arbitrary current distribution using the method of Green's functions. We use this to derive an analytic form for an hourglass magnetic field pattern created by electrical currents that are concentrated near (but not confined within) the equatorial plane of a cylindrical coordinate system. Our solution is not characterized by a cusp at the equatorial plane, as in previous solutions based on a current sheet. The pattern we derive provides a very good fit to hourglass magnetic field patterns emerging from three-dimensional numerical simulations of core formation, and can in principle be used for source-fitting of observed magnetic hourglass patterns.
The measurement and analysis of the magnetic field of a synchrotron light source magnet
Graf, Udo Werner
section of the magnet shows the symmetric distribution of the coils about the center line of the magnet. The iron yolk which surrounds the conductors is thermally insulated to enhance the efficiency of the cooling system. The entire magnet assembly... of charged particles in a 21 conductor that are exposed to an electric and a magnetic field. The force experienced by these particles is characterized by the Lorentz Equation, F=q(E+vxB) (3) The conductor used for the Hall probe has the shape of a...
The Magnificent Seven: Nearby Isolated Neutron Stars with strong Magnetic Fields
F. Haberl
Although the true origin of the broad absorption lines in X-ray spectra of thermal isolated neutron stars is not clear yet, our current knowledge about the "magnificent seven" strongly suggests that they are highly magnetized ($10^{13} - 10^{14}$ G), slowly rotating cooling neutron stars. Further timing studies would be very useful to obtain more independent estimates of the magnetic field strength (as they currently only exist from RX J0720.4-3125).
Gravitational Hertz experiment with electromagnetic radiation in a strong magnetic field
N. I. Kolosnitsyn; V. N. Rudenko
Brief review of principal ideas in respect of the high frequency gravitational radiation generated and detected in the laboratory condition is presented. Interaction of electro-magnetic and gravitational waves into a strong magnetic field is considered as a more promising variant of the laboratory GW-Hertz experiment. The formulae of the direct and inverse Gertsenshtein-Zeldovich effect are derived. Numerical estimates are given and a discussion of a possibility of observation of these effects in a lab is carried out.
The Magnetic Fields of Classical T Tauri Stars
Christopher M. Johns-Krull
We report new magnetic field measurements for 14 classical T Tauri stars (CTTSs). We combine these data with one previous field determination in order to compare our observed field strengths with the field strengths predicted by magnetospheric accretion models. We use literature data on the stellar mass, radius, rotation period, and disk accretion rate to predict the field strength that should be present on each of our stars according to these magnetospheric accretion models. We show that our measured field values do not correlate with the field strengths predicted by simple magnetospheric accretion theory. We also use our field strength measurements and literature X-ray luminosity data to test a recent relationship expressing X-ray luminosity as a function of surface magnetic flux derived from various solar feature and main sequence star measurements. We find that the T Tauri stars we have observed have weaker than expected X-ray emission by over an order of magnitude on average using this relationship. We suggest the cause for this is actually a result of the very strong fields on these stars which decreases the efficiency with which gas motions in the photosphere can tangle magnetic flux tubes in the corona.
Solar nebula magnetic fields recorded in the Semarkona meteorite
Fu, Roger R.; Weiss, Benjamin P.; Lima, Eduardo A.; Harrison, Richard J.; Bai, Xue-Ning; Desch, Steven J.; Ebel, Denton S.; Suavet, Clement; Wang, Huapei; Glenn, David; Le Sage, David; Kasama, Takeshi; Walsworth, Ronald L.; Kuan, Aaron T.
images of all three vector 492 Ā components of the magnetic field produced by the sample in the plane of NV sensors using 493 Ā optically-detected magnetic resonance (ODMR) spectroscopy. In this technique, described by 494 Ā Le Sage et al. (74... Ā Figure 1. Dusty olivine-bearing chondrules from the Semarkona meteorite. (A) Optical 224 Ā photomicrograph of chondrule DOC4 showing the location of dusty olivine grains. Image taken 225 Ā in reflected light with crossed polarizers. (B) Annular...
Modeling the magnetic field in the protostellar source NGC 1333 IRAS 4A
Jose Goncalves; Daniele Galli; Josep M. Girart
Magnetic fields are believed to play a crucial role in the process of star formation. We compare high-angular resolution observations of the submillimeter polarized emission of NGC 1333 IRAS 4A, tracing the magnetic field around a low-mass protostar, with models of the collapse of magnetized molecular cloud cores. Assuming a uniform dust alignment efficiency, we computed the Stokes parameters and synthetic polarization maps from the model density and magnetic field distribution by integrations along the line-of-sight and convolution with the interferometric response. The synthetic maps are in good agreement with the data. The best-fitting models were obtained for a protostellar mass of 0.8 solar masses, of age 9e4 yr, formed in a cloud with an initial mass-to-flux ratio ~2 times the critical value. The magnetic field morphology in NGC 1333 IRAS 4A is consistent with the standard theoretical scenario for the formation of solar-type stars, where well-ordered, large-scale, rather than turbulent, magnetic fields control the evolution and collapse of the molecular cloud cores from which stars form.
Observation of Dirac Monopoles in a Synthetic Magnetic Field
M. W. Ray; E. Ruokokoski; S. Kandel; M. M÷tt÷nen; D. S. Hall
Magnetic monopoles --- particles that behave as isolated north or south magnetic poles --- have been the subject of speculation since the first detailed observations of magnetism several hundred years ago. Numerous theoretical investigations and hitherto unsuccessful experimental searches have followed Dirac's 1931 development of a theory of monopoles consistent with both quantum mechanics and the gauge invariance of the electromagnetic field. The existence of even a single Dirac magnetic monopole would have far-reaching physical consequences, most famously explaining the quantization of electric charge. Although analogues of magnetic monopoles have been found in exotic spin-ices and other systems, there has been no direct experimental observation of Dirac monopoles within a medium described by a quantum field, such as superfluid helium-3. Here we demonstrate the controlled creation of Dirac monopoles in the synthetic magnetic field produced by a spinor Bose-Einstein condensate. Monopoles are identified, in both experiments and matching numerical simulations, at the termini of vortex lines within the condensate. By directly imaging such a vortex line, the presence of a monopole may be discerned from the experimental data alone. These real-space images provide conclusive and long-awaited experimental evidence of the existence of Dirac monopoles. Our result provides an unprecedented opportunity to observe and manipulate these quantum-mechanical entities in a controlled environment.
Electric and magnetic fields and field derivatives from lightning stepped leaders and first return strokes measured at distances
Florida, University of
Electric and magnetic fields and field derivatives from lightning stepped leaders and first return; published 5 September 2008. [1] Using electric and magnetic field and field derivative sensors arrayed over-peak width of the stepped-leader/return-stroke electric field waveform; the stepped-leader electric field
Enhancement of accelerating field of microwave cavities by magnetic insulation
Stratakis, D.; Gallardo, J.; Palmer, R.B.
Limitations on the maximum achievable accelerating gradient of microwave cavities can strongly influence the performance, length, and cost of particle accelerators. Gradient limitations are widely believed to be initiated by electron emission from the cavity surfaces. Here, we show that the deleterious effects of field emission are effectively suppressed by applying a tangential magnetic field to the cavity walls. With the aid of numerical simulations we compute the field strength required to insulate an 805 MHz cavity and estimate the cavity's tolerances to typical experimental errors such as magnet misalignments and positioning errors. Then, we review an experimental program, currently under progress, to further study the concept. Finally, we report on two specific examples that illustrate the feasibility of magnetic insulation into prospective particle accelerator applications.
New dynamo pattern revealed by solar helical magnetic fields
Zhang, Hongqi; Pevtsov, A; Gao, Yu; Xu, Haiqing; Sokoloff, D D; Kuzanyan, K
Previously unobservable mirror asymmetry of the solar magnetic field -- a key ingredient of the dynamo mechanism which is believed to drive the 11-year activity cycle -- has now been measured. This was achieved through systematic monitoring of solar active regions carried out for more than 20 years at observatories in Mees, Huairou, and Mitaka. In this paper we report on detailed analysis of vector magnetic field data, obtained at Huairou Solar Observing Station in China. Electric current helicity (the product of current and magnetic field component in the same direction) was estimated from the data and a latitude-time plot of solar helicity during the last two solar cycles has been produced. We find that like sunspots helicity patterns propagate equatorwards but unlike sunspot polarity helicity in each solar hemisphere does not change sign from cycle to cycle - confirming the theory. There are, however, two significant time-latitudinal domains in each cycle when the sign does briefly invert. Our findings she...
Electron vortex beams in a magnetic field and spin filter
Debashree Chowdhury; Banasri Basu; Pratul Bandyopadhyay
We investigate the propagation of electron vortex beams in a magnetic field. It is pointed out that when electron vortex beams carrying orbital angular momentum propagate in a magnetic field, the Berry curvature associated with the scalar electron moving in a cyclic path around the vortex line is modified from that in free space. This alters the spin-orbit interaction, which affects the propagation of nonparaxial beams. The electron vortex beams with tilted vortex lead to spin Hall effect in free space. In presence of a magnetic field in time space we have spin filtering such that either positive or negative spin states emerge in spin Hall currents with clustering of spin $\\frac{1}{2}$ states.
Holographic non-Fermi liquid in a background magnetic field
Basu, Pallab; He Jianyang; Mukherjee, Anindya; Shieh, Hsien-Hang [Department of Physics and Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, B.C. V6T 1Z1 (Canada)
We study the effects of a nonzero magnetic field on a class of 2+1 dimensional non-Fermi liquids, recently found in [Hong Liu, John McGreevy, and David Vegh, arXiv:0903.2477.] by considering properties of a Fermionic probe in an extremal AdS{sup 4} black hole background. Introducing a similar fermionic probe in a dyonic AdS{sup 4} black hole geometry, we find that the effect of a magnetic field could be incorporated in a rescaling of the probe fermion's charge. From this simple fact, we observe interesting effects like gradual disappearance of the Fermi surface and quasiparticle peaks at large magnetic fields and changes in other properties of the system. We also find Landau level like structures and oscillatory phenomena similar to the de-Haas-van Alphen effect.
Engineering Weyl nodes in Dirac semimetals by a magnetic field
E. V. Gorbar; V. A. Miransky; I. A. Shovkovy
We study the phase diagram of a Dirac semimetal in a magnetic field at a nonzero charge density. It is shown that there exists a critical value of the chemical potential at which a first-order phase transition takes place. At subcritical values of the chemical potential the ground state is a gapped state with a dynamically generated Dirac mass and a broken chiral symmetry. The supercritical phase is the normal (gapless) phase with a nontrivial chiral structure: it is a Weyl semimetal with a pair of Weyl nodes for each of the original Dirac points. The nodes are separated by a dynamically induced chiral shift. The direction of the chiral shift coincides with that of the magnetic field and its magnitude is determined by the quasiparticle charge density, the strength of the magnetic field, and the strength of the interaction. The rearrangement of the Fermi surface accompanying this phase transition is described.
Radiofrequency hydrogen ion source with permanent magnets providing axial magnetic field
Oikawa, Kohei, E-mail: email@example.com; Saito, Yuta; Komizunai, Shota; Takahashi, Kazunori; Ando, Akira [Department of Electrical Engineering, Tohoku University, Sendai 980-8579 (Japan)] [Department of Electrical Engineering, Tohoku University, Sendai 980-8579 (Japan)
Uniform axial magnetic field of about 70 G is applied to a radiofrequency (rf) hydrogen ion source by arrays of permanent magnets. The plasma density and electron temperature downstream of the source and near the magnetic filter are compared with those in the previously described ion source, where the axial field has been applied by two solenoids. The source is operated at ?350 kHz and above 10 kW rf power with a field-effect-transistor-based invertor power supply in 1.5 Pa hydrogen. The results show that the plasma density of ?10{sup 19} m{sup ?3} near the source exit and ?10{sup 18} m{sup ?3} near the magnetic filter can be obtained, which are higher than those with the solenoids.
Chiral Magnetic Effect in Protoneutron Stars and Magnetic Field Spectral Evolution
Sigl, G³nter
We investigate the evolution of the chiral magnetic instability in a protoneutron star and compute the resulting magnetic power and helicity spectra. The instability may act during the early cooling phase of the hot protoneutron star after supernova core collapse, where it can contribute to the buildup of magnetic fields of strength up to the order of $10^{14}$ G. The maximal field strengths generated by this instability, however, depend considerably on the temperature of the protoneutron star, on density fluctuations and turbulence spectrum of the medium. At the end of the hot cooling phase the magnetic field tends to be concentrated around the submillimeter to cm scale, where it is subject to slow resistive damping.
Tokamaks with high-performance resistive magnets: advanced test reactors and prospects for commercial applications
Bromberg, L.; Cohn, D.R.; Williams, J.E.C.; Becker, H.; Leclaire, R.; Yang, T.
Scoping studies have been made of tokamak reactors with high performance resistive magnets which maximize advantages gained from high field operation and reduced shielding requirements, and minimize resistive power requirements. High field operation can provide very high values of fusion power density and n tau/sub e/ while the resistive power losses can be kept relatively small. Relatively high values of Q' = Fusion Power/Magnet Resistive Power can be obtained. The use of high field also facilitates operation in the DD-DT advanced fuel mode. The general engineering and operational features of machines with high performance magnets are discussed. Illustrative parameters are given for advanced test reactors and for possible commercial reactors. Commercial applications that are discussed are the production of fissile fuel, electricity generation with and without fissioning blankets and synthetic fuel production.
Exploring Ultrahigh Magnetic Field Processing of Materials for Developing Customized Microstructures and Enhanced Performance
Ludtka, GERALD M.
Thermodynamic calculations based on Gibbs free energy in the magnetization-magnetic intensity-temperature (M-H-T) magnetic equation of state space demonstrate that significantly different phase equilibria may result for those material systems where the product and parent phases exhibit different magnetization responses. These calculations show that the Gibbs free energy is changed by a factor equal to -MdH, where M and H are the magnetization and applied field strength, respectively. Magnetic field processing is directly applicable to a multitude of alloys and compounds for dramatically influencing phase stability and phase transformations. This ability to selectively control microstructural stability and alter transformation kinetics through appropriate selection of the magnetic field strength promises to provide a very robust mechanism for developing and tailoring enhanced microstructures (and even nanostructures through accelerated kinetics) with superior properties for a broad spectrum of material applications. For this Industrial Materials for the Future (IMF) Advanced Materials for the Future project, ferrous alloys were studied initially since this alloy family exhibits ferromagnetism over part of its temperature range of stability and therefore would demonstrate the maximum impact of this novel processing mechanism. Additionally, with these ferrous alloys, the high-temperature parent phase, austenite, exhibits a significantly different magnetization response from the potential product phases, ferrite plus carbide or martensite; and therefore, the solid-state transformation behavior of these alloys will be dramatically influenced by the presence of ultrahigh magnetic fields. Finally, a thermodynamic calculation capability (within ThermoCalc for example) was developed during this project to enable parametric studies to be performed to predict the magnitude of the influence of magnetic processing variables on the phase stability (phase diagrams) in ferromagnetic materials of relevance to the Industries of the Future (IOF).
Quantum field theory in a magnetic field: From quantum chromodynamics to graphene and Dirac semimetals
Vladimir A. Miransky; Igor A. Shovkovy
A range of quantum field theoretical phenomena driven by external magnetic fields and their applications in relativistic systems and quasirelativistic condensed matter ones, such as graphene and Dirac/Weyl semimetals, are reviewed. We start by introducing the underlying physics of the magnetic catalysis. The dimensional reduction of the low-energy dynamics of relativistic fermions in an external magnetic field is explained and its role in catalyzing spontaneous symmetry breaking is emphasized. The general theoretical consideration is supplemented by the analysis of the magnetic catalysis in quantum electrodynamics, chromodynamics and quasirelativistic models relevant for condensed matter physics. By generalizing the ideas of the magnetic catalysis to the case of nonzero density and temperature, we argue that other interesting phenomena take place. The chiral magnetic and chiral separation effects are perhaps the most interesting among them. In addition to the general discussion of the physics underlying chiral magnetic and separation effects, we also review their possible phenomenological implications in heavy-ion collisions and compact stars. We also discuss the application of the magnetic catalysis ideas for the description of the quantum Hall effect in monolayer and bilayer graphene, and conclude that the generalized magnetic catalysis, including both the magnetic catalysis condensates and the quantum Hall ferromagnetic ones, lies at the basis of this phenomenon. We also consider how an external magnetic field affects the underlying physics in a class of three-dimensional quasirelativistic condensed matter systems, Dirac semimetals. While at sufficiently low temperatures and zero density of charge carriers, such semimetals are expected to reveal the regime of the magnetic catalysis, the regime of Weyl semimetals with chiral asymmetry is realized at nonzero density...
Quantum field theory in a magnetic field: From quantum chromodynamics to graphene and Dirac semimetals
Vladimir A. Miransky; Igor A. Shovkovy
A range of quantum field theoretical phenomena driven by external magnetic fields and their applications in relativistic systems and quasirelativistic condensed matter ones, such as graphene and Dirac/Weyl semimetals, are reviewed. We start by introducing the underlying physics of the magnetic catalysis. The dimensional reduction of the low-energy dynamics of relativistic fermions in an external magnetic field is explained and its role in catalyzing spontaneous symmetry breaking is emphasized. The general theoretical consideration is supplemented by the analysis of the magnetic catalysis in quantum electrodynamics, chromodynamics and quasirelativistic models relevant for condensed matter physics. By generalizing the ideas of the magnetic catalysis to the case of nonzero density and temperature, we argue that other interesting phenomena take place. The chiral magnetic and chiral separation effects are perhaps the most interesting among them. In addition to the general discussion of the physics underlying chiral magnetic and separation effects, we also review their possible phenomenological implications in heavy-ion collisions and compact stars. We also discuss the application of the magnetic catalysis ideas for the description of the quantum Hall effect in monolayer and bilayer graphene, and conclude that the generalized magnetic catalysis, including both the magnetic catalysis condensates and the quantum Hall ferromagnetic ones, lies at the basis of this phenomenon. We also consider how an external magnetic field affects the underlying physics in a class of three-dimensional quasirelativistic condensed matter systems, Dirac semimetals. While at sufficiently low temperatures and zero density of charge carriers, such semimetals are expected to reveal the regime of the magnetic catalysis, the regime of Weyl semimetals with chiral asymmetry is realized at nonzero density...
Advanced magnetic calculations for high magnetic field compact ion source T. Thuillier, J.-C. Curdy, T. Lamy, P. Sole, P. Sortais, J.-L. Vieux-Rochaz and D. Voulot
Boyer, Edmond
sextupolar confinement and HTS wire technology for axial field. The 3D non-linear calculations have been]. The technical datasheets for HTS superconductors wires is available on American Superconductors (AMS) web site[3. The wire is 0.3 mm thick and 4 mm wide and can handle up to ~263 Mpa stress at 77 K. HTS coil is composed
National High Magnetic Field Laboratory moves closer
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AFDC Printable Version Share this resource Send a link to EERE: Alternative Fuels Data Center Home Page to someone by E-mail Share EERE: Alternative Fuels Data Center Home Page on Facebook Tweet about EERE: Alternative Fuels Data Center Home Page on Twitter Bookmark EERE: Alternative1 First Use of Energy for All Purposes (Fuel and Nonfuel), 2002; Level:Energy: Grid Integration Redefining What's Possible for Renewable Energy:Nanowire Solar Energy Harvestingproducts (CDPs) that
Monte Carlo characterization of skin doses in 6 MV transverse field MRI-linac systems: Effect of field size, surface orientation, magnetic field strength, and exit bolus
Oborn, B. M.; Metcalfe, P. E.; Butson, M. J.; Rosenfeld, A. B. [Illawarra Cancer Care Centre (ICCC), Wollongong, New South Wales 2500 (Australia) and Centre for Medical Radiation Physics (CMRP), University of Wollongong, Wollongong, New South Wales 2500 (Australia); Centre for Medical Radiation Physics (CMRP), University of Wollongong, Wollongong, New South Wales 2500 (Australia); Illawarra Cancer Care Centre (ICCC), Wollongong, New South Wales 2500 (Australia); Centre for Medical Radiation Physics (CMRP), University of Wollongong, Wollongong, New South Wales 2500 (Australia)
Purpose: The main focus of this work is to continue investigations into the Monte Carlo predicted skin doses seen in MRI-guided radiotherapy. In particular, the authors aim to characterize the 70 {mu}m skin doses over a larger range of magnetic field strength and x-ray field size than in the current literature. The effect of surface orientation on both the entry and exit sides is also studied. Finally, the use of exit bolus is also investigated for minimizing the negative effects of the electron return effect (ERE) on the exit skin dose. Methods: High resolution GEANT4 Monte Carlo simulations of a water phantom exposed to a 6 MV x-ray beam (Varian 2100C) have been performed. Transverse magnetic fields of strengths between 0 and 3 T have been applied to a 30x30x20 cm{sup 3} phantom. This phantom is also altered to have variable entry and exit surfaces with respect to the beam central axis and they range from -75 deg. to +75 deg. The exit bolus simulated is a 1 cm thick (water equivalent) slab located on the beam exit side. Results: On the entry side, significant skin doses at the beam central axis are reported for large positive surface angles and strong magnetic fields. However, over the entry surface angle range of -30 deg. to -60 deg., the entry skin dose is comparable to or less than the zero magnetic field skin dose, regardless of magnetic field strength and field size. On the exit side, moderate to high central axis skin dose increases are expected except at large positive surface angles. For exit bolus of 1 cm thickness, the central axis exit skin dose becomes an almost consistent value regardless of magnetic field strength or exit surface angle. This is due to the almost complete absorption of the ERE electrons by the bolus. Conclusions: There is an ideal entry angle range of -30 deg. to -60 deg. where entry skin dose is comparable to or less than the zero magnetic field skin dose. Other than this, the entry skin dose increases are significant, especially at higher magnetic fields. On the exit side there is mostly moderate to high skin dose increases for 0.2-3 T with the only exception being large positive angles. Exit bolus of 1 cm thickness will have a significant impact on lowering such exit skin dose increases that occur as a result of the ERE.
On the Magnetic Field of Pulsars with Realistic Neutron Stars Configurations
Riccardo Belvedere; Jorge Armando Rueda; Remo Ruffini
We have recently developed a neutron star model fulfilling global and not local charge neutrality, both in the static and in the uniformly rotating cases. The model is described by the coupled Einstein-Maxwell-Thomas- Fermi (EMTF) equations, in which all fundamental interactions are accounted for in the framework of general relativity and relativistic mean field theory. Uniform rotation is introduced following the Hartle's formalism. We show that the use of realistic parameters of rotating neutron stars obtained from numerical integration of the self-consistent axisymmetric general relativistic equations of equilibrium leads to values of the magnetic field and radiation efficiency of pulsars very different from estimates based on fiducial parameters assuming a neutron star mass, M = 1.4 Msun, radius R = 10 km, and moment of inertia, I = 10^45 g cm^2. In addition, we compare and contrast the magnetic field inferred from the traditional Newtonian rotating magnetic dipole model with respect to the one obtained from its general relativistic analog which takes into due account the effect of the finite size of the source. We apply these considerations to the specific high-magnetic field pulsars class and show that, indeed, all these sources can be described as canonical pulsars driven by the rotational energy of the neutron star, and with magnetic fields lower than the quantum critical field for any value of the neutron star mass.
Residual Dipolar Couplings in Zero-to-Ultra-Low-Field Nuclear Magnetic Resonance
Blanchard, John W; King, Jonathan P; Ledbetter, Micah P; Levine, Emma H; Bajaj, Vikram S; Budker, Dmitry; Pines, Alexander
Zero-to-ultra-low-field nuclear magnetic resonance (ZULF-NMR) provides a new regime for the measurement of nuclear spin-spin interactions free from effects of large magnetic fields, such as truncation of terms that do not commute with the Zeeman Hamiltonian. One such interaction, the magnetic dipole-dipole coupling, is a valuable source of spatial information in NMR, though many terms are unobservable in high-field NMR, and the interaction averages to zero under isotropic molecular tumbling. Under partial orientational ordering, this information is retained in the form of so-called residual dipolar couplings. We report zero-to-ultra-low-field NMR measurements of residual dipolar couplings in acetonitrile-2-$^{13}$C aligned in stretched polyvinyl acetate gels. This represents the first investigation of dipolar couplings as a perturbation on the indirect spin-spin $J$-coupling in the absence of an applied magnetic field. As a consequence of working at zero magnetic field, we observe terms of the dipole-dipole c...
Electric and Magnetic Fields (EMF) RAPID Engineering Program, Project 7: Development of Field Exposure Models
Bracken, T.D.; Rankin, R.F.; Wiley, J.A.
The purpose of this project was to develop a conceptual model for estimating magnetic field (EMF) personal exposure (PE) of individuals or groups and construct a working model using existing data.
Ultra-low field nuclear magnetic resonance and magnetic resonance imaging to discriminate and identify materials
Kraus, Robert H. (Los Alamos, NM); Matlashov, Andrei N. (Los Alamos, NM); Espy, Michelle A. (Los Alamos, NM); Volegov, Petr L. (Los Alamos, NM)
An ultra-low magnetic field NMR system can non-invasively examine containers. Database matching techniques can then identify hazardous materials within the containers. Ultra-low field NMR systems are ideal for this purpose because they do not require large powerful magnets and because they can examine materials enclosed in conductive shells such as lead shells. The NMR examination technique can be combined with ultra-low field NMR imaging, where an NMR image is obtained and analyzed to identify target volumes. Spatial sensitivity encoding can also be used to identify target volumes. After the target volumes are identified the NMR measurement technique can be used to identify their contents.
On collisional diffusion in a stochastic magnetic field
Abdullaev, S. S. [Forschungszentrum J³lich GmbH, Institut f³r Energie- und Klimaforschung - Plasmaphysik, EURATOM Association, 52425 J³lich (Germany)] [Forschungszentrum J³lich GmbH, Institut f³r Energie- und Klimaforschung - Plasmaphysik, EURATOM Association, 52425 J³lich (Germany)
The effect of particle collisions on the transport in a stochastic magnetic field in tokamaks is investigated. The model of resonant magnetic perturbations generated by external coils at the plasma edge is used for the stochastic magnetic field. The particle collisions are simulated by a random walk process along the magnetic field lines and the jumps across the field lines at the collision instants. The dependencies of the local diffusion coefficients on the mean free path ?{sub mfp}, the diffusion coefficients of field lines D{sub FL}, and the collisional diffusion coefficients, ?{sub ?} are studied. Based on these numerical data and the heuristic arguments, the empirical formula, D{sub r}=?{sub ?}+v{sub ||}D{sub FL}/(1+L{sub c}/?{sub mfp}), for the local diffusion coefficient is proposed, where L{sub c} is the characteristic length of order of the connection length l{sub c}=?qR{sub 0}, q is the safety factor, R{sub 0} is the major radius. The formula quite well describes the results of numerical simulations. In the limiting cases, the formula describes the Rechester-Rosenbluth and Laval scalings.
The onset of ion heating during magnetic reconnection with a strong guide field
Drake, J. F., E-mail: email@example.com [Space Science Laboratory, University of California, Berkeley, California 94720 (United States); Swisdak, M., E-mail: firstname.lastname@example.com [Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, Maryland 20742 (United States)
The onset of the acceleration of ions during magnetic reconnection is explored via particle-in-cell simulations in the limit of a strong ambient guide field that self-consistently and simultaneously follow the motions of protons and ? particles. Heating parallel to the local magnetic field during reconnection with a guide field is strongly reduced compared with the reconnection of anti-parallel magnetic fields. The dominant heating of thermal ions during guide field reconnection results from pickup behavior of ions during their entry into reconnection exhausts and dominantly produces heating perpendicular rather than parallel to the local magnetic field. Pickup behavior requires that the ion transit time across the exhaust boundary (with a transverse scale of the order of the ion sound Larmor radius) be short compared with the ion cyclotron period. This translates into a threshold in the strength of reconnecting magnetic field that favors the heating of ions with high mass-to-charge. A simulation with a broad initial current layer produces a reconnecting system in which the amplitude of the reconnecting magnetic field just upstream of the dissipation region increases with time as reconnection proceeds. The sharp onset of perpendicular heating when the pickup threshold is crossed is documented. A comparison of the time variation of the parallel and perpendicular ion heating with that predicted based on the strength of the reconnecting field establishes the scaling of ion heating with ambient parameters both below and above the pickup threshold. The relevance to observations of ion heating in the solar corona is discussed.
Formation of magnetic discontinuities through superposition of force-free magnetic fields: Periodic boundaries
Kumar, Dinesh; Bhattacharyya, R. [Udaipur Solar Observatory, Physical Research Laboratory, Dewali, Bari Road, Udaipur-313001 (India)] [Udaipur Solar Observatory, Physical Research Laboratory, Dewali, Bari Road, Udaipur-313001 (India); Smolarkiewicz, P. K. [European Centre for Medium-Range Weather Forecasts, Reading RG2 9AX (United Kingdom)] [European Centre for Medium-Range Weather Forecasts, Reading RG2 9AX (United Kingdom)
In ideal magnetohydrodynamics characterized by an infinite electrical conductivity, the magnetic flux across an arbitrary fluid surface is conserved in time. The magnetofluid then can be partitioned into contiguous subvolumes of fluid, each of which entraps its own subsystem of magnetic flux. During dynamical evolution of the magnetofluid, these subvolumes press into each other; and in the process, two such subvolumes may come into direct contact while ejecting a third interstitial subvolume. Depending on the orientations of magnetic fields of the two interacting subvolumes, the magnetic field at the common surface of interaction may become discontinuous and a current sheet is formed there. This process of current sheet formation and their subsequent decay is believed to be a plausible mechanism for coronal heating and may also be responsible for various eruptive phenomena at the solar corona. In this work, we explore this theoretical concept through numerical simulations of a viscous, incompressible magnetofluid characterized by infinite electrical conductivity. In particular, we show that if the initial magnetic field is prescribed by superposition of two linear force-free fields with different torsion coefficients, then formation of current sheets are numerically realizable in the neighborhood of magnetic nulls.
Kinetic models of current sheets with a sheared magnetic field
Mingalev, O. V.; Mingalev, I. V.; Mel'nik, M. N. [Russian Academy of Sciences, Polar Geophysical Institute, Cola Science Center (Russian Federation); Artemyev, A. V.; Malova, H. V.; Popov, V. Yu. [Russian Academy of Sciences, Space Research Institute (Russian Federation); Chao, Shen [Chinese Academy of Sciences, Center for Space Science and Applied Research (China); Zelenyi, L. M. [Russian Academy of Sciences, Space Research Institute (Russian Federation)
Thin current sheets, whose existence in the Earth's magnetotail is confirmed by numerous spacecraft measurements, are studied analytically and numerically. The thickness of such sheets is on the order of the ion Larmor radius, and the normal component of the magnetic field (B{sub z}) in the sheet is almost constant, while the tangential (B{sub x}) and shear (B{sub y}) components depend on the transverse coordinate z. The current density in the sheet also has two self-consistent components (j{sub x} and j{sub y}, respectively), and the magnetic field lines are deformed and do not lie in a single plane. To study such quasi-one-dimensional current configurations, two kinetic models are used, in particular, a numerical model based on the particle-in-cell method and an analytical model. The calculated results show that two different modes of the self-consistent shear magnetic field B{sub y} and, accordingly, two thin current sheet configurations can exist for the same input parameters. For the mode with an antisymmetric z profile of the B{sub y} component, the magnetic field lines within the sheet are twisted, whereas the profiles of the plasma density, current density component j{sub y}, and magnetic field component B{sub x} differ slightly from those in the case of a shearless magnetic field (B{sub y} = 0). For the symmetric B{sub y} mode, the magnetic field lines lie in a curved surface. In this case, the plasma density in the sheet varies slightly and the current sheet is two times thicker. Analysis of the dependence of the current sheet structure on the flow anisotropy shows that the sheet thickness decreases significantly with decreasing ratio between the thermal and drift plasma velocities, which is caused by the dynamics of quasi-adiabatic ions. It is shown that the results of the analytical and numerical models are in good agreement. The problems of application of these models to describe current sheets at the magnetopause and near magnetic reconnection regions are discussed.
High-frequency electric field measurement using a toroidal antenna
Lee, Ki Ha (Lafayette, CA)
A simple and compact method and apparatus for detecting high frequency electric fields, particularly in the frequency range of 1 MHz to 100 MHz, uses a compact toroidal antenna. For typical geophysical applications the sensor will be used to detect electric fields for a wide range of spectrum starting from about 1 MHz, in particular in the frequency range between 1 to 100 MHz, to detect small objects in the upper few meters of the ground. Time-varying magnetic fields associated with time-varying electric fields induce an emf (voltage) in a toroidal coil. The electric field at the center of (and perpendicular to the plane of) the toroid is shown to be linearly related to this induced voltage. By measuring the voltage across a toroidal coil one can easily and accurately determine the electric field.
Harper, G. M. [School of Physics, Trinity College, Dublin 2 (Ireland)
Recently, it has been proposed that the winds of non-pulsating and non-dusty K and M giants and supergiants may be driven by some form of magnetic pressure acting on highly clumped wind material. While many researchers believe that magnetic processes are responsible for cool evolved stellar winds, existing MHD and Alfven wave-driven wind models have magnetic fields that are essentially radial and tied to the photosphere. The clumped magnetic wind scenario is quite different in that the magnetic flux is also being carried away from the star with the wind. We test this clumped wind hypothesis by computing continuum radio fluxes from the {zeta} Aur semiempirical model of Baade et al., which is based on wind-scattered line profiles. The radio continuum opacity is proportional to the electron density squared, while the line scattering opacity is proportional to the gas density. This difference in proportionality provides a test for the presence of large clumping factors. We derive the radial distribution of clump factors (CFs) for {zeta} Aur by comparing the nonthermal pressures required to produce the semiempirical velocity distribution with the expected thermal pressures. The CFs are {approx}5 throughout the sub-sonic inner wind region and then decline outward. These implied clumping factors lead to excess radio emission at 2.0 cm, while at 6.2 cm it improves agreement with the smooth unclumped model. Smaller clumping factors of {approx}2 lead to better overall agreement but also increase the discrepancy at 2 cm. These results do not support the magnetic clumped wind hypothesis and instead suggest that inherent uncertainties in the underlying semiempirical model probably dominate uncertainties in predicted radio fluxes. However, new ultraviolet line and radio continuum observations are needed to test the new generations of inhomogeneous magnetohydrodynamic wind models.
Screening magnetic fields by superconductors: A simple model
Caputo, J.-G., E-mail: email@example.com [Laboratoire de Mathķmatiques, INSA de Rouen, Avenue de l'Universitķ, 76801 Saint-Etienne du Rouvray (France); Gozzelino, L.; Laviano, F.; Ghigo, G.; Gerbaldo, R. [Department of Applied Science and Technology, Politecnico di Torino, 10129, Torino (Italy); Noudem, J.; Thimont, Y.; Bernstein, P. [CRISMAT/LUSAC, Physics Department, Universitķ de Caen (France)
We introduce a simple approach to evaluate the magnetic field distribution around superconducting samples, based on the London equations; the elementary variable is the vector potential. This procedure has no adjustable parameters, only the sample geometry and the London length, ?, determine the solution. This approach was validated by comparing the induction field calculated to the one measured above MgB{sub 2} disks of different diameters, at 20?K and for applied fields lower than 0.4?T. The model can be applied if the flux line penetration inside the sample can be neglected when calculating the induction field distribution outside the superconductor. We conclude by showing on a cup-shape geometry how one can design a magnetic shield satisfying a specific constraint.
Hull, Charles L. H.; Plambeck, Richard L.; Bower, Geoffrey C.; Heiles, Carl; Meredith Hughes, A. [Astronomy Department and Radio Astronomy Laboratory, University of California, Berkeley, CA 94720-3411 (United States); Bolatto, Alberto D.; Jameson, Katherine; Mundy, Lee; Pound, Marc W. [Astronomy Department and Laboratory for Millimeter-wave Astronomy, University of Maryland, College Park, MD 20742 (United States); Carpenter, John M.; Lamb, James W.; Pillai, Thushara [Department of Astronomy, California Institute of Technology, 1200 E. California Blvd., MC 249-17, Pasadena, CA 91125 (United States); Crutcher, Richard M.; Hakobian, Nicholas S.; Kwon, Woojin; Looney, Leslie W. [Department of Astronomy, University of Illinois at Urbana-Champaign, 1002 W Green Street, Urbana, IL 61801 (United States); Fiege, Jason D.; Franzmann, Erica [Department of Physics and Astronomy, University of Manitoba, Winnipeg, MB R3T 2N2 (Canada); Houde, Martin [Department of Physics and Astronomy, University of Western Ontario, London, ON N6A 3K7 (Canada); Matthews, Brenda C., E-mail: firstname.lastname@example.com [Department of Physics and Astronomy, University of Victoria, 3800 Finnerty Rd., Victoria, BC V8P 5C2 (Canada); and others
We present results of {lambda}1.3 mm dust-polarization observations toward 16 nearby, low-mass protostars, mapped with {approx}2.''5 resolution at CARMA. The results show that magnetic fields in protostellar cores on scales of {approx}1000 AU are not tightly aligned with outflows from the protostars. Rather, the data are consistent with scenarios where outflows and magnetic fields are preferentially misaligned (perpendicular), or where they are randomly aligned. If one assumes that outflows emerge along the rotation axes of circumstellar disks, and that the outflows have not disrupted the fields in the surrounding material, then our results imply that the disks are not aligned with the fields in the cores from which they formed.
Dynamics of Mesoscale Magnetic Field in Diffusive Shock Acceleration
P. H. Diamond; M. A. Malkov
We present a theory for the generation of mesoscale ($kr_{g}\\ll 1$, where $r_{g}$ is the cosmic ray gyroradius) magnetic fields during diffusive shock acceleration. The decay or modulational instability of resonantly excited Alfven waves scattering off ambient density perturbations in the shock environment naturally generates larger scale fields. For a broad spectrum of perturbations, the physical mechanism of energy transfer is random refraction, represented by diffusion of Alfven wave packet in $k-$space. The scattering field can be produced directly by the decay instability or by the Drury instability, a hydrodynamic instability driven by the cosmic ray pressure gradient. This process is of interest to acceleration since it generates waves of longer wavelength, and so enables the confinement and acceleration of higher energy particles. This process also limits the intensity of resonantly generated turbulent magnetic field on $r_{g}$ scales.
Superconducting FCL using a combined inducted magnetic field trigger and shunt coil
Tekletsadik, Kasegn D. (Rexford, NY)
A single trigger/shunt coil is utilized for combined induced magnetic field triggering and shunt impedance. The single coil connected in parallel with the high temperature superconducting element, is designed to generate a circulating current in the parallel circuit during normal operation to aid triggering the high temperature superconducting element to quench in the event of a fault. The circulating current is generated by an induced voltage in the coil, when the system current flows through the high temperature superconducting element.
Nuclear magnetic resonances in weak fields
Mitchell, Richard Warren
' The snalInr 30. voltages necessary in this case would allow the use of parallel banks of batteries, which should increase the stability of the cux xwnt. Lf batteries are used as a ycwsr source, no. 6 wire should be a convenient siss for prodcci...&g fields uy to 106 gauss in a sole noid of the dinensions used here. Pour banks of batterissx each bank containing five batteries in serissx should pxxxvide ~te stabili RIGDIILATTOM FXELUi 'Ae two wain difficulties with the pxesent nodulation scheme...
Ground-state magnetic phase diagram of bow-tie graphene nanoflakes in external magnetic field
Sza?owski, Karol, E-mail: email@example.com, E-mail: email@example.com [Department of Solid State Physics, Faculty of Physics and Applied Informatics, University of ?¾d?, ul. Pomorska 149/153, 90-236 ?¾d? (Poland)
The magnetic phase diagram of a ground state is studied theoretically for graphene nanoflakes of bow-tie shape and various sizes in external in-plane magnetic field. The tight-binding Hamiltonian supplemented with Hubbard term is used to model the electronic structure of the systems in question. The existence of the antiferromagnetic phase with magnetic moments localized at the sides of the bow-tie is found for low field and a field-induced spin-flip transition to ferromagnetic state is predicted to occur in charge-undoped structures. For small nanoflake doped with a single charge carrier, the low-field phase is ferrimagnetic and a metamagnetic transition to ferromagnetic ordering can be forced by the field. The critical field is found to decrease with increasing size of the nanoflake. The influence of diagonal and off-diagonal disorder on the mentioned magnetic properties is studied. The effect of off-diagonal disorder is found to be more important than that of diagonal disorder, leading to significantly widened distribution of critical fields for disordered population of nanoflakes.
Plasma Equilibrium in a Magnetic Field with Stochastic Regions
J.A. Krommes and Allan H. Reiman
The nature of plasma equilibrium in a magnetic field with stochastic regions is examined. It is shown that the magnetic differential equation that determines the equilibrium Pfirsch-Schluter currents can be cast in a form similar to various nonlinear equations for a turbulent plasma, allowing application of the mathematical methods of statistical turbulence theory. An analytically tractable model, previously studied in the context of resonance-broadening theory, is applied with particular attention paid to the periodicity constraints required in toroidal configurations. It is shown that even a very weak radial diffusion of the magnetic field lines can have a significant effect on the equilibrium in the neighborhood of the rational surfaces, strongly modifying the near-resonant Pfirsch-Schluter currents. Implications for the numerical calculation of 3D equilibria are discussed
Tunable dynamic response of magnetic gels: impact of structural properties and magnetic fields
Mitsusuke Tarama; Peet Cremer; Dmitry Y. Borin; Stefan Odenbach; Hartmut L÷wen; Andreas M. Menzel
Ferrogels and magnetic elastomers feature mechanical properties that can be reversibly tuned from outside through magnetic fields. Here we concentrate on the question how their dynamic response can be adjusted. The influence of three factors on the dynamic behavior is demonstrated using appropriate minimal models: first, the orientational memory imprinted into one class of the materials during their synthesis; second, the structural arrangement of the magnetic particles in the materials; and third, the strength of an external magnetic field. To illustrate the latter point, structural data are extracted from a real experimental sample and analyzed. Understanding how internal structural properties and external influences impact the dominant dynamical properties helps to design materials that optimize the requested behavior.
Tiwari, Sanjiv Kumar, E-mail: email@example.com [Udaipur Solar Observatory, Physical Research Laboratory, Dewali, Bari Road, Udaipur 313 001 (India)
A magnetic field is force-free if there is no interaction between it and the plasma in the surrounding atmosphere, i.e., electric currents are aligned with the magnetic field, giving rise to zero Lorentz force. The computation of various magnetic parameters, such as magnetic energy (using the virial theorem), gradient of twist of sunspot magnetic fields (computed from the force-free parameter {alpha}), and any kind of extrapolation, heavily hinges on the force-free approximation of the photospheric sunspot magnetic fields. Thus, it is of vital importance to inspect the force-free behavior of sunspot magnetic fields. The force-free nature of sunspot magnetic fields has been examined earlier by some researchers, ending with incoherent results. Accurate photospheric vector field measurements with high spatial resolution are required to inspect the force-free nature of sunspots. For this purpose, we use several vector magnetograms of high spatial resolution obtained from the Solar Optical Telescope/Spectro-Polarimeter on board Hinode. Both the necessary and sufficient conditions for force-free nature are examined by checking the global and local nature of equilibrium magnetic forces over sunspots. We find that sunspot magnetic fields are not very far from the force-free configuration, although they are not completely force-free on the photosphere. The umbral and inner penumbral fields are more force-free than the middle and outer penumbral fields. During their evolution, sunspot magnetic fields are found to maintain their proximity to force-free field behavior. Although a dependence of net Lorentz force components is seen on the evolutionary stages of the sunspots, we do not find a systematic relationship between the nature of sunspot magnetic fields and the associated flare activity. Further, we examine whether the fields at the photosphere follow linear or nonlinear force-free conditions. After examining this in various complex and simple sunspots, we conclude that, in either case, photospheric sunspot magnetic fields are closer to satisfying the nonlinear force-free field approximation.
Lesson Summary Students will learn about the magnetic fields of
Mojzsis, Stephen J.
Lesson Summary Students will learn about the magnetic fields of the Sun and Earth. This activity if they have learned them in another context and you can remind them about those lessons in this activity minutes 1. Read and review the lesson plan 2. Gather required materials 3. Form student teams Exploring
Relationship Between Solar Wind Speed and Coronal Magnetic Field Properties
Fujiki, Ken'ichi; Iju, Tomoya; Hakamada, Kazuyuki; Kojima, Masayoshi
We have studied the relationship between the solar-wind speed $[V]$ and the coronal magnetic-field properties (a flux expansion factor [$f$] and photospheric magnetic-field strength [$B_{\\mathrm{S}}$]) at all latitudes using data of interplanetary scintillation and solar magnetic field obtained for 24 years from 1986 to 2009. Using a cross-correlation analyses, we verified that $V$ is inversely proportional to $f$ and found that $V$ tends to increase with $B_{\\mathrm{S}}$ if $f$ is the same. As a consequence, we find that $V$ has extremely good linear correlation with $B_{\\mathrm{S}}/f$. However, this linear relation of $V$ and $B_{\\mathrm{S}}/f$ cannot be used for predicting the solar-wind velocity without information on the solar-wind mass flux. We discuss why the inverse relation between $V$ and $f$ has been successfully used for solar-wind velocity prediction, even though it does not explicitly include the mass flux and magnetic-field strength, which are important physical parameters for solar-wind accele...
Energy Eigenvalues of Kemmer Equation for a Homogeneous Magnetic Field
A. Havare; K. Sogut
This article illustrates a completely algebraic method to obtain the energy levels of a massive spin-1 particle moving in a constant magnetic field. In the process to obtain the energy levels the wave function was written by harmonic oscillator solutions.
Universal formulae for thermoelectric transport with magnetic field and disorder
Andrea Amoretti; Daniele Musso
We obtain explicit expressions for the thermoelectric transport coefficients of a strongly coupled, planar medium in the presence of an orthogonal magnetic field and disorder. The computations are performed within the gauge/gravity framework, however we propose and argue for a possible universal relevance of the results relying on comparisons and extensions of previous hydrodynamical analyses and experimental data.
A linear helicon plasma device with controllable magnetic field gradient
Barada, Kshitish K.; Chattopadhyay, P. K.; Ghosh, J.; Kumar, Sunil; Saxena, Y. C. [Institute for Plasma Research, Bhat, Gandhinagar, Gujarat 382428 (India)
Current free double layers (CFDLs) are localized potential structures having spatial dimensions - Debye lengths and potential drops of more than local electron temperature across them. CFDLs do not need a current for them to be sustained and hence they differ from the current driven double layers. Helicon antenna produced plasmas in an expanded chamber along with an expanding magnetic field have shown the existence of CFDL near the expansion region. A helicon plasma device has been designed, fabricated, and installed in the Institute for Plasma Research, India to study the role of maximum magnetic field gradient as well as its location with respect to the geometrical expansion region of the chamber in CFDL formation. The special feature of this machine consisting of two chambers of different radii is its capability of producing different magnetic field gradients near the physical boundary between the two chambers either by changing current in one particular coil in the direction opposite to that in other coils and/or by varying the position of this particular coil. Although, the machine is primarily designed for CFDL experiments, it is also capable of carrying out many basic plasma physics experiments such as wave propagation, wave coupling, and plasma instabilities in a varying magnetic field topology. In this paper, we will present the details of the machine construction, its specialties, and some preliminary results about the production and characterization of helicon plasma in this machine.
Triggering for Magnetic Field Measurements of the LCLS Undulators
Hacker, Kirsten
A triggering system for magnetic field measurements of the LCLS undulators has been built with a National Instruments PXI-1002 and a Xylinx FPGA board. The system generates single triggers at specified positions, regardless of encoder sensor jitter about a linear scale.
Mathematical Modeling of Magnetic Field Profiles in Superconductors
Wetton, Brian
Mathematical Modeling of Magnetic Field Profiles in Superconductors Michael Lindstrom, Brian Wetton, Rob Kiefl March 1, 2011 Abstract One of the defining characteristics of a superconductor is the Meiss results. 1 Introduction to the Problem and the Model Superconductors are materials which exhibit a phase
Universal formulae for thermoelectric transport with magnetic field and disorder
Amoretti, Andrea
We obtain explicit expressions for the thermoelectric transport coefficients of a strongly coupled, planar medium in the presence of an orthogonal magnetic field and disorder. The computations are performed within the gauge/gravity framework, however we propose and argue for a possible universal relevance of the results relying on comparisons and extensions of previous hydrodynamical analyses and experimental data.
Photon-Axion conversions in transversely inhomogeneous magnetic fields
Javier Redondo
We compute the photon-axion conversion probability in an external magnetic field with a strong transverse gradient in the eikonal approximation for plane waves. We find it typically smaller than a comparable uniform case. Some insights into the phenomenon of photon-axion splitting are given.
Spin flip probability of electron in a uniform magnetic field
Hammond, Richard T. [Department of Physics, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina and Army Research Office, Research Triangle Park, North Carolina 27703 (United States)
The probability that an electromagnetic wave can flip the spin of an electron is calculated. It is assumed that the electron resides in a uniform magnetic field and interacts with an incoming electromagnetic pulse. The scattering matrix is constructed and the time needed to flip the spin is calculated.
Method for the detection of a magnetic field utilizing a magnetic vortex
Novosad, Valentyn (Chicago, IL); Buchanan, Kristen (Batavia, IL)
The determination of the strength of an in-plane magnetic field utilizing one or more magnetically-soft, ferromagnetic member, having a shape, size and material whereas a single magnetic vortex is formed at remanence in each ferromagnetic member. The preferred shape is a thin circle, or dot. Multiple ferromagnetic members can also be stacked on-top of each other and separated by a non-magnetic spacer. The resulting sensor is hysteresis free. The sensor's sensitivity, and magnetic saturation characteristics may be easily tuned by simply altering the material, size, shape, or a combination thereof to match the desired sensitivity and saturation characteristics. The sensor is self-resetting at remanence and therefore does not require any pinning techniques.
Critical currents of YBCO tapes and Bi-2212 wires at different temperatures and magnetic fields
Lombardo, V.; Barzi, e.; Turrioni, D.; Zlobin, A.V.; /Fermilab
Design studies for the cooling channel of a Muon Collider call for straight and helical solenoids generating field well in excess of the critical fields of state of the art Low Temperature Superconductors (LTS) such as Nb{sub 3}Sn or NbTi. Therefore, High Temperature Superconductors (HTS) will need to be used for the manufacturing of all or certain sections of such magnets to be able to generate and withstand the field levels at the cryogenic temperatures required by the new machine. In this work, two major High Temperature Superconductors - Bi2212 round wires and YBCO coated conductor tapes - are investigated to understand how critical current density of such conductors scales as a function of external field and operating temperature. This is vital information to make conductor choices depending on the application and to proceed with the design of such magnets.
Magnetic field measurements at milliarcsecond resolution around massive young stellar objects
Surcis, G; van Langevelde, H J; Kramer, B Hutawarakorn; Bartkiewicz, A; Engelkamp, H
Magnetic fields have only recently been included in theoretical simulations of high-mass star formation. The simulations show that magnetic fields can play a crucial role not only in the formation and dynamics of molecular outflows, but also in the evolution of circumstellar disks. Therefore, new measurements of magnetic fields at milliarcsecond resolution close to massive young stellar objects (YSOs) are fundamental for providing new input for numerical simulations and for understanding the formation process of massive stars. The polarized emission of 6.7 GHz CH3OH masers allows us to investigate the magnetic field close to the massive YSO where the outflows and disks are formed. Recently, we have detected with the EVN CH3OH maser polarized emission towards 10 massive YSOs. From a first statistical analysis we have found evidence that magnetic fields are primarily oriented along the molecular outflows. To improve our statistics we are carrying on a large observational EVN campaign for a total of 19 sources, ...
Laser-driven platform for generation and characterization of strong quasi-static magnetic fields
Santos, J J; Giuffrida, L; Forestier-Colleoni, P; Fujioka, S; Zhang, Z; Korneev, Ph; Bouillaud, R; Dorard, S; Batani, D; Chevrot, M; Cross, J; Crowston, R; Dubois, J -L; Gazave, J; Gregori, G; d'HumiĶres, E; Hulin, S; Ishihara, K; Kojima, S; Loyez, E; MarquĶs, J -R; Morace, A; Nicola', Ph; Peyrusse, O; Poyķ, A; Raffestin, D; Ribolzi, J; Roth, M; Schaumann, G; Serres, F; Tikhonchuk, V T; Vacar, Ph; Woolsey, N
Quasi-static magnetic-fields up to $800\\,$T are generated in the interaction of intense laser pulses (500J, 1ns, 10^{17}W/cm^2) with capacitor-coil targets of different materials. The reproducible magnetic-field was consistently measured by three independent diagnostics: GHz-bandwidth inductor pickup coils (B-dot probes), Faraday rotation of polarized optical laser light and proton beam-deflectometry. The field rise time is consistent with the laser pulse duration, and it has a dipole-like distribution over a characteristic volume of 1mm^3, which is coherent with theoretical expectations. These results demonstrate a very efficient conversion of the laser energy into magnetic fields, thus establishing a robust laser-driven platform for reproducible, well characterized, generation of quasi-static magnetic fields at the kT-level, as well as for magnetization and accurate probing of high-energy-density samples driven by secondary powerful laser or particle beams.
Model for Synchrotron Emission from Shell Supernova Remnants in Nonuniform Interstellar Medium and Nonuniform Magnetic Field
O. Petruk
Possibility to model the high energy synchrotron emission (in X- and gamma-rays) from supernova remnants is an important task for modern astronomy and astrophysics, because it may be responsible for the nonthermal X-rays and TeV gamma-rays observed recently from a number of SNRs. This emission allows as to look in the processes of particle acceleration on SNR shocks and generation of cosmic rays. In this paper, a model for the synchrotron emission from shell SNR in nonuniform interstellar medium and nonuniform magnetic field is presented. This model is a generalization of the model of Reynolds and Chevalier developed for a spherical SNR in the uniform medium and uniform magnetic field. The model will be used for studies on the thermal and nonthermal X-ray images and spectra from nonspherical SNRs in different interstellar magnetic field configurations.
Turbulence and magnetic field amplification from spiral SASI modes in core-collapse supernovae
Endeve, Eirik [ORNL; Cardall, Christian Y [ORNL; Budiardja, Reuben D [ORNL; Blondin, John [ORNL; Mezzacappa, Anthony [ORNL
The stationary accretion shock instability (SASI) plays a central role in modern simulations of the explosion phase of core-collapse supernovae (CCSNe). It may be key to realizing neutrino powered explosions, and possibly links birth properties of pulsars (e.g., kick, spin, and magnetic field) to supernova dynamics. Using high-resolution magnetohydrodynamic simulations, we study the development of turbulence, and subsequent amplification of magnetic fields in a simplified model of the post-bounce core-collapse supernova environment. Turbulence develops from secondary instabilities induced by the SASI. Our simulations suggest that the development of turbulence plays an important role for the subsequent evolution of the SASI. The turbulence also acts to amplify weak magnetic fields via a small-scale dynamo.
Florinski, V. [Department of Physics, University of Alabama, Huntsville, AL 35899 (United States); Alouani-Bibi, F.; Guo, X. [Center for Space Plasma and Aeronomic Research, University of Alabama, Huntsville, AL 35899 (United States); Kota, J. [Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721 (United States)
Very high intensities of galactic cosmic rays measured by Voyager 1 in the heliosheath appear to be incompatible with the presence of a modulation 'wall' near the heliopause produced by a pile up of the heliospheric magnetic field. We propose that the modulation wall is a structure permeable to cosmic rays as a result of a sectored magnetic field topology compressed by plasma slowdown on approach to the heliopause and stretched to high latitudes by latitudinal flows in the heliosheath. The tightly folded warped current sheet permits efficient cosmic-ray transport in the radial direction via a drift-like mechanism. We show that when stochastic variations in the sector widths are taken into account, particle transport becomes predominantly diffusive both along and across the magnetic sectors. Using a test-particle model for cosmic rays in the heliosheath we investigate the dependence of the diffusion coefficients on the properties of the sector structure and on particle energy.
Noninvasive valve monitor using constant magnetic and/or DC electromagnetic field
Casada, Donald A. (Knoxville, TN); Haynes, Howard D. (Knoxville, TN)
One or more sources of steady magnetic field are carefully located on the outside of a valve body. The constant magnetic field is transmitted into the valve body and valve internals. A magnetic field detector carefully located on the outside of the valve body detects the intensity of the magnetic field at its location. As the position of a valve internal part is changed, there is an alteration in the magnetic field in the valve, and a consequent change in the detected magnetic field. Changes in the detected signal provide an indication of the position and motion of the valve internals.
Apparatus for unilateral generation of a homogeneous magnetic field
Fukushima, E.; Rath, A.R.; Roeder, S.B.W.
An apparatus for unilaterally producing a substantially homogeneous magnetic field. The apparatus includes two circular electromagnet coils, a small coil and a large coil, which are coaxial with one another and which are separated by a distance equal to one-half the difference in the radius of the two coils. By appropriate selection of electrical currents, which are passed through the coils in opposite directions, a region of homogeneous magnetic field is formed. This region is centered on the common axis of the two coils, at a point on the axis which is at a distance from the small coil equal to one-half the radius of the small coil, and which is on the opposite side of the small coil from the large coil. The apparatus has particular application in the field of diagnostic medical NMR and other NMR applications.
Apparatus for unilateral generation of a homogeneous magnetic field
Fukushima, Eiichi (Los Alamos, NM); Rath, Alan R. (San Diego, CA); Roeder, Stephen B. W. (La Mesa, CA)
An apparatus for unilaterally producing a substantially homogeneous magnetic field. The apparatus includes two circular electromagnet coils, a small coil and a large coil, which are coaxial with one another and which are separated by a distance equal to one-half the difference in the radius of the two coils. By appropriate selection of electrical currents, which are passed through the coil in opposite directions, a region of homogeneous magnetic field is formed. This region is centered on the common axis of the two coils, at a point on the axis which is at a distance from the small coil equal to one-half the radius of the small coil, and which is on the opposite side of the small coil from the large coil. The apparatus has particular application in the field of diagnostic medical NMR and other NMR applications.