Automated Activation Procedure for GaAs Photocathodes at Photo-CATCH*

Abstract

Photo-electron sources using GaAs-based photocathodes are used to provide high-brightness and high-current beams of (spin-polarized) electrons for accelerator applications such as free-electron lasers (FELs) and energy recovery linacs (ERLs). Such cathodes require a thin surface layer to achieve negative electron affinity (NEA) for photoemission. The layer is deposited during an activation procedure that greatly influences the resulting quantum efficiency of the photocathode and robustness of the layer. To standardize this process, the automatization of the activation procedure is investigated for operational use in an accelerator. This contribution presents first proof-of-principle studies of a basic automated activation procedure at TU Darmstadt's EPICS-controlled photocathode test stand Photo-CATCH. Using a co-deposition scheme with Cs and O 2 , several automated activations have been performed. Eight out of nine consecutive automated activations were successful, yielding a mean quantum efficiency of (4.9 ± 0.8) %, corresponding to a factor of 0.8 ± 0.2 relative to manual operation, and reproducibility to within ±15 %.