ILC @ SLAC R&D Program for a Polarized RF Gun ∗

Photocathode rf guns produce high-energy low-emittance electron beams. DC guns utilizing GaAs photocathodes have proven successful for generating polarized electron beams for accelerators, but they require rf bunching systems that significantly increase the transverse emittance of the beam. With higher extraction field and beam energy, rf guns can support higher current densities at the cathode. The source laser system can then be used to generate the high peak current, relatively low duty-factor micropulses required by the ILC without the need for post-extraction rf bunching. The net result is that the injection system for a polarized rf gun can be identical to that for an unpolarized rf gun. However, there is some uncertainty as to the survivability of an activated GaAs cathode in the environment of an operating rf gun. Consequently, before attempting to design a polarized rf gun for the ILC, SLAC plans to develop an rf test gun to demonstrate the rf operating conditions suitable for an activated GaAs cathode.