CS-K-TE PHOTO CATHODES - A PROMISING ELECTRON SOURCE FOR FREE-ELECTRON LASERS

The characteristics of Cs-K-Te photo-cathodes when used in a photo-cat hode linear accelerator will be presented together with a short review of their photo-emissive properties. The cathodes have been illuminate d by light pulses obtained by frequency quadrupling the light of a Nd: YLF laser. The emitted electrons have been accelerated in a 1.3 GHz RF linear accelerator operating at an energy of 6 MeV. The quantum effic iency of the Cs-K-Te cathodes at 259 nm decreases exponentially with o peration time, but recovers partially during storage in UHV between su ccessive operating sessions. These two effects tend to compensate for long times, so that saturation of the quantum efficiency value at abou t 2% is reached after 20 h of operation. A Cs-K-Te cathode, degraded b y use in the accelerator, can be rejuvenated to about 60% of its initi al quantum efficiency by heating it to 120 degrees C for 1 hour. (C) 1 998 Elsevier Science B.V. All rights reserved.