• P. Emma, R.F. Boyce, A. Brachmann, R. Carr, F.-J. Decker, Y.T. Ding, D. Dowell, S.A. Edstrom, J.C. Frisch, A. Gilevich, G.R. Hays, P. Hering, Z. Huang, R.H. Iverson, Yu.I. Levashov, H. Loos, A. Miahnahri, H.-D. Nuhn, B.D. Poling, D.F. Ratner, J.L. Turner, J.J. Welch, W.E. White, Z.R. Wolf, J. Wu
  SLAC, Menlo Park, California
• S. Spampinati
  ELETTRA, Basovizza

Funding: Work supported by the U.S. Dept. of Energy contract #DE-AC02-76SF00515.

The Linac Coherent Light Source (LCLS) is an x-ray Free-Electron Laser (FEL) project presently in a commissioning phase at SLAC. The very bright electron beam required for the FEL is also susceptible to a micro-bunching instability* in the magnetic bunch compressors, prior to the FEL undulator. The uncorrelated electron energy spread can be increased by an order of magnitude to provide strong Landau damping against the instability without degrading the free-electron laser performance. To this end, a ‘laser-heater’ system has been installed in the LCLS injector, which modulates the energy of a 135-MeV electron bunch with an IR laser beam in a short undulator, enclosed within a four-dipole chicane. The last half of the chicane time-smears the energy modulation leaving an effective thermal energy spread increase. We present the first commissioning results of this system, its operational issues, and its impact on the micro-bunching instability.

*Z. Huang et. al., Phys. Rev. ST Accel. Beams 7, 074401 (2004).

• J. Wu, R. Akre, A. Brachmann, P. Chu, F.-J. Decker, Y.T. Ding, D. Dowell, S.A. Edstrom, P. Emma, D. Fairley, J.C. Frisch, A. Gilevich, G.R. Hays, P. Hering, Z. Huang, R.H. Iverson, H. Loos, A. Miahnahri, H.-D. Nuhn, D.F. Ratner, J.L. Turner, J.J. Welch, W.E. White, D. Xiang
  SLAC, Menlo Park, California
• E. Meier
  ASCo, Clayton, Victoria

Funding: Work supported by Department of Energy contract DE-AC02-76SF00515. This work was performed in support of the LCLS project at SLAC

The Linac Coherent Light Source is an x-ray Free-Electron Laser (FEL) project being commissioned at SLAC. The very bright electron beam required for the FEL is subjected to various sources of jitter along the accelerator. The peak current, centroid energy, and trajectory of the electron bunch are controlled precisely at the highest repetition rate possible with feedback systems. We report commissioning experience for these systems. In particular, there is high frequency content in the electron bunch current spectrum, and we report its impact on the systems. Due to the coupling of the betatron motion and the dispersion component of the electron trajectory, a fast in-line model* is incorporated. For the longitudinal feedback, we report the performance of two different configurations: one with RF system as direct actuators, which are nonlinear, and the other with artificially formed linear energy and energy-chirp actuators. Since the electron bunch is compressed to a final peak current of 2 to 3 kA, coherent synchrotron radiation and other wakefields are included for precise control of the electron bunch parameters. Machine performance is compared to start-to-end simulations.

*P. Chu et al., these PAC09 proceedings