First setup for cooled GaAs cathodes with increased charge lifetime

Abstract

GaAs photocathodes can be used for generation of highly polarized electron beams. For high- current applications it is necessary to maximize the charge lifetime of the cathode material to ensure reliable operation. It is expected to increase the local vacuum conditions by cryogenic cooling of the electrode and a local subvolume, due to cryogenic adsorption of reactive residual gas molecules at the surrounding walls. This both protects the sensitive negative-electron-affinity surface of the cathode and allows a higher laser power deposited in the material, resulting in higher possible beam currents. An electrostatic bend is introduced to reduce Ion-backbombardment and further increase the cathode lifetime. To measure the characteristics of such a cryogenic source, a dedicated set-up is being developed at the Photo-CATCH test facility in Darmstadt, Germany.