Experimental study of GaAs photocathode performance in RF gun

A prototype of an S-band RF photogun with a GaAs photocathode has been built and tested at Novosibirsk. The main goal of this prototype is to check the possibility of long time operation for the GaAs photocathode in a strong accelerating field of an RF cavity. The first experimental results concerning dark current and the lifetime of a GaAs photocathode in the negative electron affinity (NEA) condition under high RF power are presented. The dark current observed is much higher than predicted. A possible mechanism for large dark current emission from a NEA surface is suggested and discussed.