Development of a Cryogenic DC Photoelectron Gun for GaAs Cathodes with Increased Charge Lifetime

Entwicklung einer kryogenen DC-Photoelektronen-Kanone für GaAs-Kathoden mit verlängerter Ladungslebensdauer

PhD thesis

Description:GaAs photocathodes provide a source of highly polarized electron beams. To ensure reliable operation for high current applications it is necessary to increase charge lifetime. To improve the local vacuum condition around the cathode the use of a cryogenic sub-volume is proposed. It is expected that the cryogenic adsorption of reactive residual-gas molecules yield an enhanced lifetime of the negative-electron-affinity surface of the cathode. Additional cooling of the cathode itself allows a higher laser power to be deposited in the material, resulting in higher possible beam currents.

During this work, a prototype of a cryogenic DC photo-electron gun was designed, assembled and tested. The chosen design aims at reducing ion back-bombardment on the photo-cathode surface by further improving vacuum conditions. For this purpose, the photo-cathode is placed inside an almost closed cryogenic sub-volume.

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

Picture of the cryogenic sub-volume mounted on the cryocooler, which is used to cool the volume und works with a closed helium cycle.

Publications

Tobias Eggert: Development of a Cryogenic DC Photoelectron Gun for GaAs Cathodes with Increased Charge Lifetime. Dissertation (TU Darmstadt, 2023)