• A. Brachmann, F.-J. Decker, Y.T. Ding, D. Dowell, P. Emma, J.C. Frisch, A. Gilevich, G.R. Hays, P. Hering, Z. Huang, R.H. Iverson, H. Loos, A. Miahnahri, D. Nordlund, H.-D. Nuhn, P.A. Pianetta, J.L. Turner, J.J. Welch, W.E. White, J. Wu, D. Xiang
  SLAC, Menlo Park, California

Surface characterization of the LCLS RF gun cathode A. Brachmann On behalf of the LCLS commissioning team The first copper cathode installed in the LCLS RF gun was used during LCLS commissioning for more than a year. However, after high charge operation (~ 500 pC), the cathode showed a decline of quantum efficiency due to surface contamination caused by residual ionized gas species present in the vacuum system. We report results of SEM, XPS and XAS studies that were carried out on this cathode after it was removed from the gun. X-ray absorption and X-ray photoelectron spectroscopy reveal surface contamination by various hydrocarbon compounds. In addition we report on the performance of the second installed cathode with emphasis on the spatial distribution of electron emission.

• J.C. Frisch, C. Bostedt, J.D. Bozek, A. Brachmann, R.N. Coffee, F.-J. Decker, Y.T. Ding, D. Dowell, P. Emma, A. Gilevich, G. Haller, G.R. Hays, P. Hering, B.L. Hill, Z. Huang, R.H. Iverson, E.P. Kanter, B. Kraessig, H. Loos, A. Miahnahri, H.-D. Nuhn, A. Perazzo, M. Petree, D.F. Ratner, T.J. Smith, S.H. Southworth, J.L. Turner, J.J. Welch, W.E. White, J. Wu, L. Young
  SLAC, Menlo Park, California
• R.B. Wilcox
  LBNL, Berkeley, California

In addition to its normal operation at 250pC, the LCLS has operated with 20pC bunches delivering X-ray beams to users with energies between 800eV and 2 keV and with bunch lengths below 10 fs FWHM. A bunch arrival time monitor and timing transmission system provide users with sub 100 fs synchronization between a laser and the X-rays for pump / probe experiments. We describe the performance and operational experience of the LCLS for short bunch experiments.