Computational Tool for Modeling and Design of Rugged GaAs- based Polarized Electron Sources

High-current, high-brightness, spin-polarized electron beams are required for next generation electron-ion colliders (EIC). Proposed cathode designs are based on negative electron affinity (NEA) GaAs. A major limitation of these cathodes is their operational lifetime due to their susceptibility to damages in electron guns. Recent experiments done in Cornell University have demonstrated that a NEA GaAs photocathode can be activated with a protective Cs2Te cap layer leading to a factor of 5 lifetime improvement due to the resistance of Cs2Te to poor vacuum and chemical poisoning. The optimum design parameters for a NEA GaAs photocathode with a protective layer are still to be determined, however, there are no available codes to efficiently explore the large number of possible material design choices. We propose to address this problem by developing software to model both charge and spin transport together with transmission of electrons across cap layer-vacuum interfaces to enable simulations for investigation and design of rugged GaAs-based photocathodes. Our overall approach is to design and implement software for high-fidelity, three-dimensional, modeling of photo-excited polarized electrons in GaAs with a protective cap layer, Monte Carlo charge and spin transport across a GaAs-layer-vacuum system, and emission into vacuum with realistic surface potentials. Simulation results from the implemented models will be verified against existing theoretical results and validated against experimental data on NEA GaAs photocathodes with protective layers. We will design software to model electron spin dynamics in simulation subregions with different material properties. Then, we will implement prototype code for modeling of spin and charge transport together with electron emission. We will run simulations to test the prototyped models for spin transport across different material layers and emission of spin-polarized electrons. The implementation will be fully three-dimensional and tested using parameters derived from Cornell University experiments.