Einfluss der verschiedenen Aktivierungsmethoden auf die Lebensdauer der GaAs Photokathode
Influence of different activation methods at the lifetime of the GaAs photokathode
In scope of this thesis were different activation methods of gallium-arsenide cathodes tested at the source of spin polarized electrons at the superconducting Darmstadt electron linear accelerator S-DALINAC. The aim of this work was to compare a regular activation with a mask activation. Because of remodeling work to create a third recirculation it was not possible to use high voltage. Therefore all measurements were done at 100 V. The source of spin polarized electrons consists three vacuum chambers. A load lock chamber for the transport of a cathode in the vacuum system, a preparation chamber for the activation of the cathode and the cathode chamber for the generation of a electron beam. With a infrared pyrometer the heat cleaning were calibrated in the load lock and preparation chamber. At a regular activation a vacuum lifetime of 1392,5 ± 176,6 hours and a beam lifetime of 5,455 ± 0,002 hours could determined. A quantum efficiency of 1 µA/mW was reached. The mask activation has unfortunately no satisfying results. Only currents at 80 nA could be extracted with quantum efficiencies at 0,002 µA/mW. Because of that there were no vacuum and beam lifetime determined by mask activation.