• C. H. Rivetta, R. Akre, P. Cutino, J. C. Frisch, K. D. Kotturi
  SLAC, Menlo Park, California

The LCLC RF gun requires a water cooling thermal system to tune the resonance frequency of the cavity to 2856.03MHz. The RF system operates in pulsed mode with bursts of 2.5usec at a repetition rate of 30-120Hz. The thermal system operates in combination with the low-level RF system to set the operation point of the cavity. The Low-Level RF system controls the magnitude and phase of the cavity voltage and define slow signals to the thermal system. The thermal system operates by pre-heating / pre-cooling the water and mixing both channels to achieve the optimal temperature to control the cavity resonant frequency. The tune control of the RF gun include two systems with different dynamics. The dynamics of the thermal system is slow while the RF system is fast. Additionally, different actuators in the system present limits that introduce non-linearities to be taking into account during the start up process . Combining these characteristics, a controller is designed for the resulting hybrid system that allows convergence in large for all the operation conditions and achieve the performance in the magnitude and phase of the cavity voltage required around the operation point.

• T. Mastorides, J. D. Fox, C. H. Rivetta, D. Teytelman, D. Van Winkle
  SLAC, Menlo Park, California

PEP-II operations will increase the beam currents to 4A for LER and 2.2A for HER to achieve the final goal in luminosity. These magnitudes are challenging in part because they will push toward the limit the longitudinal low-order mode (LOM) beam stability due to beam loading. To analyze the behavior of both rings at high currents and understand the limits in the longitudinal feedback systems a simulation tool has been developed at SLAC. This tool is based on a reduced model of the longitudinal LOM dynamics of the beam interacting with the effective impedance presented by RF station. Simulations and measurements of the longitudinal beam behavior in both rings have been performed to understand the ultimate limit of the system. These studies have defined the impact of control loop parameters in the longitudinal beam dynamics, identified the poor performance of RF devices affecting the optimal performance of the RF stations and quantified the behavior of the longitudinal LOM beam dynamics. Results of sensitivity to parameter variations in the beam dynamics and limits in the maximum current that LER/HER can achieve based on the longitudinal beam stability are reported in this paper.

• J. D. Fox, T. Mastorides, C. H. Rivetta, D. Van Winkle
  SLAC, Menlo Park, California

Several high-current accelerators use feedback techniques in the accelerating RF systems to control the impedances seen by the circulating beam. These Direct and Comb Loop architectures put the high power klystron and LLRF signal processing components inside feedback loops, and the ultimate behavior of the systems depends on the individual sub-component properties. Imperfections and non-idealities in the signal processing leads to reduced effectiveness in the impedance controlled loops. In the PEP-II LLRF systems non-linear effects have been shown to reduce the achievable beam currents, increase low-mode longitudinal growth rates and reduce the margins and stability of the LLRF control loops. We present measurements of the driver amplifiers used in the PEP-II systems, and present measurement techniques needed to quantify the small-signal gain, linearity, transient response and image frequency generation of these amplifiers. Results are presented from measurements of 5 different types of amplifiers, and the trade-offs in selecting between them highlighted.

• P. Emma, R. Akre, J. Castro, Y. T. Ding, D. Dowell, J. C. Frisch, A. Gilevich, G. R. Hays, P. Hering, Z. Huang, R. H. Iverson, P. Krejcik, C. Limborg-Deprey, H. Loos, A. Miahnahri, C. H. Rivetta, M. E. Saleski, J. F. Schmerge, D. C. Schultz, J. L. Turner, J. J. Welch, W. E. White, J. Wu
  SLAC, Menlo Park, California
• L. Froehlich, T. Limberg, E. Prat
  DESY, Hamburg

The Linac Coherent Light Source (LCLS) is a SASE x-ray Free-Electron Laser (FEL) project presently under construction at SLAC. The injector section, from drive-laser and RF photocathode gun through the first bunch compressor chicane, was installed during the Fall of 2006. Initial system commissioning with an electron beam takes place in the Spring and Summer of 2007. The second phase of construction, including the second bunch compressor and the FEL undulator, will begin later, in the Fall of 2007. We report here on experience gained during the first phase of machine commissioning, including RF photocathode gun, linac booster section, energy spectrometers, S-band and X-band RF systems, the first bunch compressor stage, and the various beam diagnostics.