Surface Treatment Experience of the All Superconducting Gun Cavities

The performance of superconducting cavities depends extremely on the material and surface properties. In the last decades processes have been developed for the successful serial production of accelerating cavities for large scale facilities like the European XFEL. A main feature of these cavities are relatively large diameter beam ports on both sides which can be used for the surface treatment processes. In contrast, superconducting gun cavities have only one beam port and a half-cell with a back-wall acting as mirror plate with some small hole for the cathode in the center. Being apparently only a small feature, it turned out to require special attention for the surface treatment. This is in particular the case, when the target gradients are as high as gradients for the accelerating cavities. In our contribution we present the experience made within the last years and how we finally achieved high gradients