Status of the R& D Program at the Gun Test Facility

The Gun Test Facility (GTF) consists of a 1.6-cell S-band photocathode gun and a single SLAC 3-m accelerating structure (booster) followed by a beam dump. The beam components are housed in the SPEAR synchrotron injector vault in Building 140. Outside the vault are the two XK5 klystrons/modulators that provide the rf power, and the laser shack and control area. The laser shack contains a high-power low repetition rate Nd:glass laser system used to produce photoelectrons from the copper cathode of the gun. Using an earlier (borrowed) version of the laser system, first beams were produced in 1997. Completion of installation and commissioning took place in 1998, and the first experimental results were obtained. In 1999, the laser system was completely replaced with a SLAC-owned, nearly duplicate, system. The purpose of the GTF from the start was to demonstrate and characterize the high-brightness beam required for the LCLS. The nominal LCLS beam at the booster exit is 1 nC of charge, 100 A, with an energy spread of {le}0.2% and a normalized rms emittance of 1 x 10{sup -6} m. To achieve this emittance, the nominal plan is to use a charge distribution at the cathode that is spatially and temporallymore » uniform, with 2-mm and 10-ps FWHM diameter and length respectively. The current LCLS R&D program was funded beginning in mid-FY99. From the start it was determined by the LCLS Project leaders that the GTF was the appropriate facility for conducting the injector R&D.« less