• R.B. Fiorito, M. Cornacchia, A.G. Shkvarunets, J.C.T. Thangaraj
  UMD, College Park, Maryland
• S. Di Mitri, M. Veronese
  ELETTRA, Basovizza
• H. Loos, J. Wu
  SLAC, Menlo Park, California

Recent observations of coherent optical transition radiation (COTR) at LCLS and other laboratories have been recognized as a signature of theμbunching instability, which affects the longitudinal phase space of the electron beam and ultimately the performance of the Free Electron Laser. In addition, the COTR emission limits the utility of OTR screens as beam profiling diagnostics. In an effort to understand and predict the extent of COTR emission and to help specify required instrumentation for new FELs, we have developed codes at UMD and SLAC-LCLS that use the output from the ELEGANT particle tracking code to predict the emission of COTR at specific wavelengths or within a band width. The COTR codes provides plots of the intensity patterns in the transverse plane, simulating a virtual OTR screen. Both incoherent and coherent intensities are produced thus providing an estimate of theμbunching gain at the observed wavelengths. Since the ELEGANT simulation of microbunching strongly depends on the number of particles, efforts have been carried out to speed up the COTR code analysis. The results of these codes applied to the LCLS and FERMI@elettra linac FELs are presented.

• G. De Ninno
  University of Nova Gorica, Nova Gorica
• E. Allaria, M. Cornacchia, G. De Ninno, S. Di Mitri, B. Diviacco, G. Penco, C. Spezzani, M. Trovò
  ELETTRA, Basovizza

The commissioning of the first stage of FERMI@Elettra will start during the summer 2009. During the first year of operation, efforts will concentrate on the optimization of the gun performance, as well as of the electron-beam acceleration and transport through the LINAC. By fall 2010, it is our aim to generate out of the LINAC an electron beam as similar as possible to the one needed for obtaining the nominal (i.e., user-required) FEL performance [see, e.g., S. Di Mitri et al., this Conference]. Such a beam will be then injected into the undulator chain and used to get the first FEL light. In this paper, we present our strategy for the commissioning of the FEL process, both in SASE and seeded configurations. On the basis of start-to-end simulations, we also discuss the expected FEL performance for day-one operation.