Towards the operation of Cs-K-Sb photocathodes in superconducting rf photoinjectors
Martin A. H. Schmeißer, Sonal Mistry, Hans Kirschner, Susanne Schubert, Andreas Jankowiak, Thorsten Kamps, Julius Kühn
DOI 10.1103/PhysRevAccelBeams.21.113401 · Physical Review Accelerators and Beams
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Abstract
High quantum efficiency photocathodes are mandatory for the operation of photoinjector driven electron accelerators with high average current and high brightness beams. Photocathodes based on bi-alkali antimonides, e.g., CsK2Sb, exhibit high quantum efficiencies for visible light and can be operated close to the photoemission threshold, thus they are suitable candidates to provide high current and low emittance electron beams. In this paper, a codeposition procedure of K and Cs on Sb resulting in high quantum efficiency photocathodes is presented and compared to the sequential growth procedure that was established for photomultiplier and accelerator applications. In-situ x-ray photoelectron spectroscopy is applied to gain insights into the reaction pathway of antimony with alkali metals, and to optimize the growth process of CsK2Sb on Mo. It has been found that the average stoichiometry of the samples is similar after both procedures. The study also presents the behavior of the photocurrent at cryogenic temperatures, the influence of cooling and warmup cycles on the photocathode lifetime and our experience with storage and transport. This work demonstrates that our codeposition growth procedure reproducibly delivers high quantum efficiency photocathodes, and that their quantum efficiency, when excited with green photons, is not influenced by cryogenic temperatures.
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