• K. Honkavaara
  Uni HH, Hamburg

The VUV-FEL being commissioned at DESY Hamburg is a user facility for SASE FEL radiation in the VUV wavelength range. The quality of the high brightness electron beam driving the VUV-FEL plays an important role for the performance of the facility. Prior to installation, the electron photo-injector of the VUV-FEL has been fully tested and characterized at the PITZ photo injector test facility at DESY Zeuthen, dedicated to develop high brightness electron sources for FEL projects like the VUV-FEL and the XFEL. We summarize the results on transverse emittance optimization at PITZ and report on the upgrade of the PITZ facility presently under construction. Results on transverse emittance optimization and measurements at the VUV-FEL are presented. Projected emittances around 1.4 mm mrad for 90% of a 1 nC bunch have been regularly measured. In addition, recent measurements of the longitudinal bunch profile after compression using a transverse deflecting cavity are presented.

• C.K. Sinclair
  Cornell University, Department of Physics, Ithaca, New York

Funding: Work supported by Cornell University, and the National Science Foundation under contract PHY-0131508

Cornell University is constructing a 100 mA average current, high brightness electron injector for a planned Energy Recovery Linac (ERL) hard X-ray synchrotron radiation source. This injector will employ a very high voltage DC gun with a negative electron affinity photoemission cathode. Relatively long duration electron pulses from the photocathode will be drift bunched, and accelerated to 5-15 MeV with five two-cell, 1300 MHz superconducting cavities. The total beam power will be limited to 575 kW by the DC and RF power sources. A genetic algorithm based computational optimization of this injector has resulted in simulated rms normalized emittances of 0.1 mm-mrad at 80 pC/bunch, and 0.7 mm-mrad at 1 nC/bunch. The many technical issues and their design solutions will be discussed. Construction of the gun and the SRF cavities is well underway. The schedule for completion, and the planned measurements, will be presented.

• O.J. Luiten, M.J. Van der Wiel
  TUE, Eindhoven

Funding: Foundation for Fundamental Research on Matter (FOM), The Netherlands

Ideal "waterbag" electron bunches - uniformly filled, hard-edged ellipsoids of charge - can be realized in practice by photoemission with properly shaped fs laser pulses [1]. The linear self-fields of such objects enable thermal-emittance-limited beams and bunch compression to the kA level. The thermal emittance may be lowered to below 0.1 micron by extracting the electrons from an ultra-cold plasma, created by photo-ionization of a cloud of laser-cooled atoms. We will present GPT simulations of the application of waterbags and cold atoms in realistic settings, based on established technology. The status of experiments will be reported.

[1] O.J. Luiten, S.B. van der Geer, M.J. de Loos, F.B. Kiewiet, and M.J. van der Wiel, Phys. Rev. Lett. 93, 094802 (2004).

• C. Limborg-Deprey
  SLAC, Menlo Park, California

Funding: SLAC is operated by Stanford University for the Department of Energy under contract number DE-AC02-76SF00515

If the laser pulse driving photoinjectors could be arbitrarily shaped, the emittance growth induced by space charge effects could be totally compensated for. In particular, for normal conducting RF guns the photo-electron distribution should approach a 3D-ellipsoidal shape. The emittance at the end of the injector would reduce to the combination of cathode emittance and RF emittance. We explore how the emittance and the brightness can be optimized for normal conducting photocathode RF gun depending on the peak current requirements. Techniques available to produce those ideal laser pulse shapes are also discussed.