Results from the average power laser experiment photocathode injector test

Tests of the electron beam injector for the Boeing/Los Alamos Average Power Laser Experiment (APLE) have demonstrated first time operation of a photocathode RF gun accelerator at 25% duty factor. This exceeds previous photocathode operation by three orders of magnitude. The success of these tests was dependent upon the development of reliable and efficient photocathode preparation and processing. This paper describes the fabrication details for photocathodes with quantum efficiencies up to 12% which were used during electron beam operation. Measurements of photocathode lifetime as it depends upon the presence of water vapor are also presented. Observations of photocathode quantum efficiency rejuvenation and extended lifetime in the RF cavities are described. The importance of these effects upon photocathode lifetime during high average power operation are discussed. ((orig.))