Long-life, high QE photocathodes

Summary form only given. Calabazas Creek Research (CCR) and the University of Maryland (UMD) are developing long life photocathodes with quantum efficiencies (QE) exceeding 2%. The research builds on reservoir cathode technology developed for thermionic cathodes, whose lifetimes was increased by approximately four times [1]. In recent research, CCR and UMD increased lifetime of cesiated tungsten photocathodes from a few hundred hours to more than 30,000 [2]. The team is extending the technology to photocathodes incorporating high QE materials, including Cs3Sb, K2CsSb, CsTe, and CsAu. Cesium Auride (CsAu) photocathodes have the advantage of being air stable prior to installation, which simplifies handling and transport. The other materials must be maintained at high vacuum, requiring specialized fabrication facilities and vacuum suitcases for transport. CCR is building a production facility in Palo Alto, CA, and UMD is establishing an advanced center for photocathode research in College Park, MD. The UMD facility will investigate issues associated with photocathode performance, including effects of surface elemental composition, surface film thickness, behavior following rejuventation, thermal effects, and angular distribution of cesium evaporation. Reservoir photocathodes include a porous tungsten substrate for the emission surface, a cesium reservoir, and an integral heater. The QE depends on the material deposited on the tungsten substrate, which will include those listed above. High QE is maintained using the integral heater to match the cesium diffusion to the evaporation rate. The development program is constructing the production facility at CCR, which will produce photocathodes for testing at UMD and other users. This will include the required handling and transport equipment and processes. The program will also test photocathodes in an RF gun at SLAC National Accelerator Laboratory. The facilities will be described and available test results presented.