Superconducting RF Photo Injectors for Future Light Sources

Future accelerator based radiation sources need high-brightness electron beams with high average currents and pulse repetition rates in the megahertz rage. Electron guns which can provide beams with these properties are still under development. The most promising candidate is the superconducting photo electron injector (SRF gun). The SRF gun operation basic principle is the direct production of short electron pulses by laser pulse irradiation of a photocathode which is placed in radio frequency resonator. The RF field ensures an instantaneous and strong acceleration of the electron bunches. The superconducting RF resonator has an extremely high quality factor of about 1010 and thus very low thermal losses which allows for a continuous operation. The SRF gun has highest gradient and acceleration voltages combination of all CW electron guns. Due to the low RF power losses, nearly all of the RF power is consumed for beam acceleration. The SRF gun vacuum is ideal with an enormous cryopumping speed to provide best lifetime for sensitive photo cathodes.

Recently a collaboration network has been formed by the four German Institutes DESY, FZD, HZB, and MBI, called SRF gun cluster, with the aim to commonly work in the research and development of SRF guns. The guns are needed for accelerator projects in Germany as the extension of the ELBE accelerator as a part of the high-intensity radiation center at FZD, the construction of compact energy recovery linac at HZB, and the continuous wave upgrade of the European XFEL at DESY. The involved institutes has longstanding experiences, know-how and capacities in the fields of superconducting radio frequency, electron gun and photo cathode development, cryogenics, electron beam diagnostics, and UV laser development. Specific common activities which have been started are focused on the SRF gun cavity development and test with a superconducting lead cathode, the cryomodule development for SRF guns, and on the semiconductor photo cathode preparation and characterization.