Activation Layer Stabilization of High Polarization Photocathodes in Sub-Optimal RF Gun Environments

The  present design of the International Linear Collider (ILC) calls for the use of a DC gun. If a radio frequency (RF) gun were employed, the pulse profile could be generated by the source laser reducing or eliminating the need for RF bunchers. To enact this scheme, a high electron spin-polarization photocathode capable of surviving the RF gun operation would be required. However, the negative-electron-affinity (NEA) photocathodes used as sources of spin-polarized electrons are currently restricted to operation only in the best of vacuum environments. Therefore, this project will create a recipe, or series of recipes, to immunize an NEA III-V photocathode against the background gasses likely to be found under operation in a generic RF gun. The protected/immunized photocathode will retain sufficient quantum yield to satisfy the ILC charge requirements and also will be a structure capable of high polarization electron emission. In Phase I, a process for producing such an emitter and introducing it into an RF gun, capable of hosting and maintaining the III-V-based high-polarization photocathodes, will be developed. Commercial Applications and other Benefits as described by the awardee: An improved environmental immunity should allow less robust photocathodes to be used in properly designed accelerator injector RF guns. The technology also will generate the foundation for a cold cathode, photon-based electron source, with small energy spread and source size limited only by the size of the exciting light spot. The evolutionary nature of the transportable GaAs photocathode could open new markets for scanning electron microscopes and other electron-based tools that can use the spin-polarized FE source for magnetic contrast imaging.