Dark Current in Superconducting Rf Photoinjectors – Measurements and Mitigation

Unwanted beam can cause beam losses and may produce acute or chronic damages of the accelerator. Furthermore it can considerably disturb experiments or increase its back-ground. The operation of the superconducting RF photo gun at the ELBE accelerator has delivered the first experimental information on that topic for this gun type. It was found, that dark current is an important issue, similar to that of normal conducting RF photo injectors. In the presentation the measurement of dark current, its properties and analysis will be shown and we will discuss ways for mitigation, especially the construction of a dark current kicker.