CRYOMODULE AND TUNING SYSTEM OF THE SUPERCONDUCTING RF PHOTO-INJECTOR*

The designs and a report on the progress in construction and testing of the cryomodule and the tuning system for the SRF gun are presented. The SRF gun project, a collaboration of BESSY, DESY, MBI and FZR, aims at the installation of a CW photo injector at the ELBE linac. The cryostat consists of a stainless steel vacuum vessel, a warm magnetic shield, a liquid N cooled thermal shield, and a He tank with two-phase supply tube. A heater pot in the He input port will be used for He level control. The 10 kW power coupler is adopted from the ELBE module. A cooling and support system for the NC photo cathode has been developed and tested. It allows the adjustment of the cathode with respect to the cavity from outside. The cryomodule will be connected with the 220 W He refrigerator of ELBE and will operate at 1.8 to 2 K. The static thermal loss is expected to be less than 20 W. Two tuners will be installed for separate tuning of the three TESLA cells and the half-cell. The tuners are dual spindle-lever systems with step motors and low-vibration gears outside the cryostat. Functionality, tuning range and accuracy have been tested in cryogenic environment