Extragalactic circuits, transmission lines, and CR particle acceleration
  A non-negligible fraction of a Supermassive Black Hole's (SMBH) rest mass energy gets transported into extragalactic space by a remarkable process in jets which are incompletely understood. What are the physical processes which transport this energy? It is likely that the energy flows electromagnetically, rather than via a particle beam flux. The deduced electromagnetic fields may produce particles of energy as high as $\sim 10^{20}$ eV. The energetics of SMBH accretion disk models and the electromagnetic energy transfer imply that a SMBH should generate a $10^{18} - 10^{19}$ Amp\`eres current close to the black hole and its accretion disk. We describe the so far best observation-based estimate of the magnitude of the current flow along the axis of the jet extending from the nucleus of the active galaxy in 3C303. The current is measured to be $I \sim 10^{18}$ Amp\`eres at $\sim 40$ kpc away from the AGN. This indicates that organized current flow remains intact over multi-kpc distances. The electric current $I$ transports electromagnetic power into free space, $P = I^{2}Z$, where $Z \sim 30$ Ohms is related to the impedance of free space, and this points to the existence of cosmic electric circuit. The associated electric potential drop, $V=IZ$, is of the order of that required to generate Ultra High Energy Cosmic Rays (UHECR). We describe the analogy of electromagnetically dominated jets with transmission lines. High powered jets {\it in vacuo} can be understood by approximate analogy with a waveguide. The importance of inductance, impedance, and other laboratory electrical concepts are discussed in this context. To appear in Proc. 18th International Symposium on Very High Energy Cosmic Ray Interactions (ISVHECR2014), CERN, Switzerland 
Philipp P. Kronberg and Richard V.E. Lovelace
astro-ph.HE