• D. Dowell, F. King, R.E. Kirby, J.F. Schmerge
  SLAC, Menlo Park, California

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

Improving and maintaining the quantum efficiency (qe) of a metal photocathode in an s-band RF gun requires a process for cleaning the surface. In this type of gun, the cathode is typically installed and the system is vacuum baked to ~200°C. If the qe is too low, the cathode is cleaned with the UV-drive laser. While laser cleaning does increase the cathode qe, it requires fluences close to the damage threshold and rastering the small diameter beam, both of which can produce non-uniform electron emission and potentially damage the cathode. This paper investigates the efficacy of a low-energy hydrogen ion beam to produce high-qe metal cathodes. Measurements of the qe vs. wavelength, surface contaminants using x-ray photoelectron spectroscopy and surface roughness were performed on copper samples, and the results showed a significant increase in qe after cleaning with a 1keV hydrogen ion beam. The H-ion beam cleans an area approximately 1cm in diameter and has no effect on the surface roughness while significantly increasing the qe. These results and a comparison with theory as well as a scheme for installing a H-ion cleaner on an s-band gun are presented.

• H. Loos, J. Castro, D. Dowell, S.M. Gierman, J.F. Schmerge
  SLAC, Menlo Park, California

Funding: Work supported by DOE contract DE-AC02-76SF00515

Understanding and optimizing the beam dynamics in high brightness electron accelerators not only requires the measurement of the 6-D beam ellipse, but also the details of the phase space distribution. By combining longitudinal and transverse phase space tomography in a dipole spectrometer the four-dimensional distribution can be resolved. We report on experiments at the Gun Test Facility (GTF) at SLAC where we measure the energy resolved horizontal beam distribution while simultaneously varying the longitudinal time-energy correlation and the horizontal phase advance to reconstruct the horizontal-longitudinal phase space distribution.

• H. Loos, P.R. Bolton, J.E. Clendenin, D. Dowell, S.M. Gierman, C. Limborg-Deprey, J.F. Schmerge
  SLAC, Menlo Park, California

Funding: Work supported by DOE contracts DE-AC02-76SF00515

The Gun Test Facility (GTF) at SLAC serves as a test bed for electron gun and high brightness photoinjector developement for future short wavelength light sources as well as new or improved diagnostics techniques. We report on measurements of longitudinal and projected as well as time-resolved transverse electron beam properies over a wide range of charge from 15 to 600 pC. The transverse and longitudinal phase space distributions are compared with simulation results.

• H. Loos, D. Dowell
  SLAC, Menlo Park, California
• M. Boscolo, M. Ferrario, C. Vicario
  INFN/LNF, Frascati (Roma)
• M. Petrarca
  INFN-Roma, Roma
• L. Serafini
  INFN-Milano, Milano
• B. Sheehy, Y. Shen, T. Tsang, X.J. Wang
  BNL, Upton, Long Island, New York

Funding: Work supported by DOE contracts DE-AC02-76SF00515 and DE-AC02-98CH10886

The photoinjectors for future short wavelength high brightness accelerator driven light sources need to produce an electron beam with ultra-low emittance. At the DUV-FEL facility at BNL, we studied the effect of longitudinally shaping the photocathode laser pulses on the electron beam dynamics. We report on measurements of transverse and longitudinal electron beam emittance and comparisons of the experimental results with simulations.