The superconducting RF photoelectron source for the ELBE accelerator at Rossendorf

Most of the proposed electron accelerator projects for future FELs, ERLs, or 4th generation light sources require electron beams with an unprecedented combination of high-brightness, low emittance and high average current. The ideal candidate for it is the superconducting RF photogun (SRF gun) which can be easily operated in CW like a DC photogun and may reach the beam quality of a normal conducting RF photogun. Challenges are the design of the superconducting cavity, the choice of the photocathode type, its life time, a possible cavity contamination, the difficulty of coupling high-average power into the gun and finally the risk of beam excitation of higher order cavity modes. At the FZ Dresden-Rossendorf a SRF gun has been developed and installed at the ELBE superconducting linac. The SRF gun is designed for an average current of 1 mA and an maximum electron energy of 9 MeV. The 1.3 GHz cavity consists of three full cells with TESLA geometry, a specially designed half-cell where the photocathode is placed. The photocathode with a Cs2Te photoemission layer is normal-conducting and cooled by liquid nitrogen. In the talk an overview of the technical concept, the RF properties, the photo cathode development, and beam parameter measurements will be given.