${\mathrm{Cs}}_x{\mathrm{K}}_y\mathrm{Sb}$ photocathodes grown on GaAs and molybdenum substrates were evaluated using a $-300\mathrm{kV}$ dc high voltage photogun and diagnostic beam line. Photocathodes grown on GaAs substrates, with varying antimony layer thickness (estimated range from $<20\mathrm{nm}$ to $>1\mathrm{um}$), yielded similar thermal emittance per rms laser spot size values ($\sim 0.4\mathrm{mm}\mathrm{mrad}/\mathrm{mm}$) but very different operating lifetime. Similar thermal emittance was obtained for a photocathode grown on a molybdenum substrate but with markedly improved lifetime. For this photocathode, no decay in quantum efficiency was measured at 4.5 mA average current and with peak current 0.55 A at the photocathode.

• Received 1 July 2020
• Accepted 9 September 2020

DOI:https://doi.org/10.1103/PhysRevAccelBeams.23.103401

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

Published by the American Physical Society