Test of the photocathode cooling system of the 3½ cell SRF gun

This paper presents results of the photocathode cooling system test of the 3½ cell SRF gun at the Forschungszentrum Rossendorf. The SRF gun will produce short electron pulses with high bunch charges and low transverse emittance. The requirement for the superconducting electron linear accelerator in Rossendorf (ELBE) is to provide a low emittance electron beam up to 1mA current and 9.5 MeV energy. Additionally, it will easily operate in continuous wave (cw) mode because of the low RF power losses in the superconducting material. Therefore, the normal conducting copper cathode must be cooled by liquid nitrogen in order to preserve the temperature of the cavity at 2.2 K. The estimated power input from the RF field into the cathode could be more than 10 W [1]. First results of temperature measurements of the photo cathode respectively from the cooling system at a heat load up to 30 W are presented.