Investigation of dark current in a S-Dalinac superconducting cavity

During the operation of the S-DALINAC, light emission associated with field emission on the surface from a 20 cell 3 GHz superconducting niobium rf cavity has been observed. The optical spectrum of the light spots has been measured by a photomultiplier using a set of filters. The obtained spectral density distribution is close to a black body radiation spectrum. In order to determine the minimum energy of the dark current electrons, measurements of bremsstrahlung spectra at the beam line exit of the accelerator have been canied out. For the interpretation of these data electron trajectory simulations based on field distributions calculated by MAFIA have been performed. Additionally, the behavior of dark current has been investigated for different ti frequencies by means of numerical calculations for TESLA and S-DALINAC cavities.