On the Photocathodes udes at the TTF Photoinjector

Since the start-up of the laser driven rf gun based photoinjector at the TESLA Test Facility (TTF) late 1998, several cathodes have been used. We report on the properties of Cs2Te and KCsTe cathodes under operating conditions, their quantum efficiency and lifetime. Darkcurrent emitted by the RF gun or the cathodes have been a major concern in the first year of operation. Meanwhile, new cathode production techniques and a conditioning effect of the RF gun has reduced the darkcurrent significantly