Status of 500kV Low Emittance Electron Gun Test Facility for a Compact X-ray Free Electron Laser at Paul Scherrer Institute

The Paul Scherrer Institute (PSI) is developing an X-ray free electron laser (XFEL) [1] which relies on photo-assisted field emission and high gradient acceleration in a low emittance electron gun (LEG). The first phase of the LEG design incorporates a sub-microsecond 500 kV pulser, a high gradient acceleration diode structure and a diagnostic electron beam line. An air core (Tesla) transformer, in critically coupled mode [2], is generating 250 ns FWHM voltage pulse to give a high gradient between the mirror finished surfaces of the cathode and anode. The emitted electron beam passes to the diagnostic beam line through a 1.5 mm hole in the anode. The measured results are compared with numeric simulations. The timing and the amplitude stability of the pulser are discussed since they are sensitive parameters for this application.