The BINP HLS to measurement vertical changes on PAL-XFEL building and   ground
  PAL-XFEL, a 4th generation light source, is currently being installed and will be completed by December of 2015 so that users can be supported beginning in 2016. PAL-XFEL equipment should continuously maintain the bunch-to-bunch beam parameter (60Hz, Energy 10GeV, Charge 200pC, Bunch Length 60fs, Emittance X/Y 0.481mm/0.256mm rad) in order to supply the energy, flux and timing of stable photons in tests by beam line users. To this end, PAL-XFEL equipment has to be kept precisely aligned (Linear Accelerator +/- 100um, Undulator +/- 50um). As a part of the process for installing PAL-XFEL, a GPS-used surface geodetic network is being constructed for precise equipment measurement and alignment, and the installation of a tunnel measurement network inside buildings is in preparation; additionally, the fiducialization of major equipment is underway. After PAL-XFEL equipment is optimized and aligned, if the ground and buildings go through vertical changes during operation, misalignment (and tilt) of equipment including various magnets and RF structures will cause errors in the electron beam trajectory, which will lead to changes to the beam parameter. For continuous and systemic measurement of vertical changes in buildings and to monitor ground sinking and uplifting, the Budker Institute of Nuclear Physics (BINP) Ultrasonic-type Hydrostatic Levelling System (HLS) is to be installed and operated in all sections of PAL-XFEL for linear accelerator, insertion device (Undulator) and beam line. This study will introduce the operation principle, design concept and advantages (self-calibration) of HLS, and will outline its installation plan and operation plan. 
Hyo-Jin Choi, Kwang-Won Seo, Kye-Hwan Gil, Seung-Hwan Kim, Heung-Sik   Kang
physics.acc-ph