Short Overview of Superconducting Photo Injectors

The success of most of the proposed ERL based electron accelerator projects for future storage ring replacements (SRR) and high power IR-FELs is contingent upon the development of an appropriate source. Electron beams with an unprecedented combination of high brightness, low emittance and high average current (hundreds of mA) are required to meet future FEL specifications.
An elegant way to create such an unique beam is to combine the high beam quality of a normal conducting RF photo guns with the superconducting technology. Such superconducting RF photo injectors (SRF gun) based on different approaches are under investigation at a growing number of institutes and companies (AES, Beijing University, BESSY, BNL, DESY, FZD, TJNAF, Niowave, NPS, Wisconsin University). Lot of progress could be achieved during the last years and first long term operation was demonstrated at the FZD.