Electron emission from GaAs photocathodes using conventional and Li-enhanced activation procedures

Emission von Elektronen aus GaAs-Photokathoden unter Verwendung von konventionellen und Li-verstärkten Aktivierungsmethoden

PhD thesis

Spin-polarized DC electron sources based on Gallium Arsenide (GaAs) photo-cathodes can be used to supply high current electron beams for energy-recovery linacs (ERLs). A thin surface layer is required to operate this type of photo-cathode in the near-infrared region, where spin-polarized electron emission is maximized. In order to meet the high demands required for ERL operation, the aim of technological developments is, among others, to improve the robustness of the surface layer in order to increase the operational lifetime of GaAs photo-cathodes.

During this project, systematic studies on photo-emission properties of GaAs photo-cathodes were conducted, with a focus on quantum efficiency and lifetime. The dependencies of these properties on the cathode activation procedure are thoroughly investigated, with a focus on the effect of Li addition to the established Cs-O and Cs-NF₃ activation procedures.

A preliminary studiy on cathode activation involving Lithium was conducted at the Upgraded Injector Test Facility (UITF) of the Thomas Jefferson National Accelerator Facility (JLab), yielding increased quantum efficiency and lifetime for Li-enhanced activation of Cs-NF₃ activations. Additional studies on Li-enhancement of Cs-O activations were conducted at Photo-CATCH, showing a significant increase in lifetime with little to no reduction of quantum efficiency.

Supported by BMBF (05H18RDRB1) and DFG (RTG 2128 “Accelence”).

Publications

M. Herbert, T. Eggert, J. Enders, M. Engart, Y. Fritzsche, M. Meier, J. Schulze, V. Wende : Negative electron-affinity activation procedures for GaAs photocathodes at Photo-CATCH. Proceedings of the 14th Int. Particle Accelerator Conf. (2023)
M. Herbert, T. Eggert, J. Enders, M. Engart, Y. Fritzsche and V. Wende : Automated Activation Procedure for GaAs Photocathodes at Photo-CATCH. 19th Workshop on Polarized Sources, Targets and Polarimetry (PSTP2022)
M. Herbert: Electron emission from GaAs photocathodes using conventional and Li-enhanced activation procedures. Dissertation (TU Darmstadt, 2022)
M. Herbert, J. Enders, M. Poelker, C. Hernandez-Garcia : Lifetime Measurements of GaAs photocathodes at the Upgraded Injector Test Facility at Jefferson Lab. Proceedings of The 18th International Workshop on Polarized Sources, Targets, and Polarimetry — PoS (PSTP2019)
M. Herbert, J. Enders, M. Espig, Y. Fritzsche, N. Kurichiyanil, M. Wagner: Status and Perspectives of the S-DALINAC Polarized-Electron Injector. Proceedings of the 8th Int. Particle Accelerator Conf. (2017)