• C.P. Hauri, R. Ganter
  PSI, Villigen

The SwissFEL requires an emittance in the range from 0.18 to 0.43 mm mrad. To achieve this ambitious goal we are developing a wavelength-tunable laser system providing powerful UV pulses with arbitrary temporal shape in the range of 3-10 ps. The system should allow exact matching of the photon energy to the work function of the cathode material and consequently the reduction of the thermal emittance. Transverse and longitudinal laser pulse shaping is foreseen to minimize nonlinear space charge forces in the electron bunch to maintain lowest emittance during acceleration. In this paper we present the design and concept of this novel laser system and show first experimental results.

• R. Ganter, B. Beutner, S. Binder, H.-H. Braun, M. Broennimann, M. Dach, T. Garvey, C.H. Gough, C.P. Hauri, M. Heiniger, R. Ischebeck, S. Ivkovic, Y. Kim, E. Kirk, F. Le Pimpec, K.B. Li, R. Luescher, P. Ming, A. Oppelt, M. Paraliev, M. Pedrozzi, J.-Y. Raguin, L. Rivkin, T. Schietinger, T. Schilcher, B. Steffen, S. Tsujino, A.F. Wrulich
  PSI, Villigen

In the frame of the SwissFEL project, an electron gun based on diode acceleration followed by a two cell RF cavity is under test at PSI. The diode consists of a photocathode / anode assembly and is driven with a voltage pulse of 500 kV maximum in 200 ns FWHM . The metal photocathode is illuminated by a Nd:YLF laser operating at 262 nm wavelength with a pulselength of 10 to 35 ps (FWHM) producing electron bunches of up to 200 pC. The distance from cathode to anode can be varied from 0 to 30 millimeters with a typical cathode field of 50 MV/m during the commissioning phase. Electrons leave the diode through an anode aperture and enter a two cells RF Cavity (1.5 GHz), which accelerates the beam to a maximum energy of 5 MeV. Beam characteristic measurements are presented and compared with simulations.