• P. Chu, J. Wu
  SLAC, Menlo Park, California
• J. Qiang
  LBNL, Berkeley, California
• G.B. Shen
  BNL, Upton, Long Island, New York

There are many simulation codes for accelerator modeling. Each one has some strength but not all. Collaboration is formed for the effort of providing a platform to host multiple modeling tools. In order to achieve such a platform, a set of common physics data structure has to be set. Application Programming Interface (API) for physics applications should also be defined within a model data provider. A preliminary platform design and prototype will be presented.

• P. Chu, S. Chevtsov, J. Wu
  SLAC, Menlo Park, California
• G.B. Shen
  BNL, Upton, Long Island, New York

High level applications often suffer from poor performance and reliability due to lengthy initialization, heavy computation and rapid graphical update. Service oriented architecture (SOA) is trying to separate the initialization and computation from applications to distributed service providers. Heavy computation such as beam tracking will be done periodically on a dedicated server and data will be available to client applications at all time. Industrial standard service architecture can help to improve the reliability and maintainability of the service providers. Robustness will also be improved by reducing the complexity of individual client applications.

• G.B. Shen
  BNL, Upton, Long Island, New York
• P. Chu, J. Wu
  SLAC, Menlo Park, California
• M.R. Kraimer
  ANL, Argonne

A modular environment for beam commissioning and operation is under development, which is based on the client/server model. The service oriented architecture consists of a server for each supported service. At NSLS-II, a so-called "virtual accelerator" has been developed, which wraps simulator engines such as Tracy and Elegant onto an EPICS system. However, with the current solution, access to data is not flexible. We are designing a new online simulator server using structured data to provide a flexible method for accessing the simulation data. This paper describes recent results of the simulator server development.

• 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.

• F.-J. Decker, R. Akre, A. Brachmann, J. Craft, Y.T. Ding, D. Dowell, P. Emma, J.C. Frisch, Z. Huang, R.H. Iverson, A. Krasnykh, H. Loos, H.-D. Nuhn, D.F. Ratner, T.J. Smith, J.L. Turner, J.J. Welch, W.E. White, J. Wu
  SLAC, Menlo Park, California

The Linac Coherent Light Source (LCLS) at SLAC is an x-ray Free Electron Laser with wavelengths of 0.15 nm to 1.5 nm. The electron beam stability is important for good lasing. While the transverse jitter of the beam is about 10-20% of the rms beam sizes, the jitter in the longitudinal phase space is a multiple of the energy spread and bunch length. At the lower energy of 4.3 GeV (corresponding to the longest wavelength of 1.5 nm) the relative energy jitter can be 0.125%, while the rms energy spread is with 0.025% five times smaller. An even bigger ratio exists for the arrival time jitter of 50 fs and the bunch duration of about 5 fs (rms) in the low charge (20 pC) operating mode. Although the impact to the experiments is reduced by providing pulse-by-pulse data of the measured energy and arrival time, it would be nice to understand and mitigate the root causes of this jitter. The thyratron of the high power supply of the RF klystrons is one of the main contributors. Another suspect is the multi-pacting in the RF loads. Phase measurements down to 0.01 degree (equals 10 fs) along the RF pulse were achieved, giving hints to the impact of the different sources.