Status of 3½ Cell Superconducting RF Gun Project in Rossendorf

In the paper, we report on the status and progress of the superconducting RF gun project in Rossendorf. The gun is designed for cw operation mode with 1 mA current and 9.5 MeV electron energy, and it will be installed at the ELBE superconducting electron linear accelerator. The gun will have a 3½ cell niobium cavity operating at 1.3 GHz. The cavity consists of three cells with TESLA geometry and a specially designed half- cell in which the photocathode will be placed. The production of two Nb cavities, with RRR 300 and 40 respectively, has be finished at the beginning of 2005. After delivery, the RF tests will be performed and the preparation of the cavities will be started. At the same time, the design of the cryostat and the fabrication of its components are already finished. Further activities are the design of the diagnostic beam line, the testing of the new photocathode preparation system, and the upgrade of the 262 nm driver laser system. electron source with high average current and low emittance for the ELBE superconducting linear accelerator and to demonstrate the capability for the future applications in FEL light sources and energy recovery linacs. This new gun can generate short pulses and high-brightness electron beams, as known from the conventional photo-injectors. Moreover, the use of the superconducting cavity allows the cw-mode operation and thus high average currents. In the proof-of- principle experiment, the operation of such a photo- injector with a half-cell cavity was successfully demonstrated (1). During about 200 hour's operation, no phenomenon of quality factor depression was observed.