• O.A. Shevchenko, N. Vinokurov
  BINP SB RAS, Novosibirsk

The new approach for the SASE radiation properties calculation was proposed recently. It is based on the use of BBGKY chain of equations, adapted for FEL. In fact, it is the only known logically correct way to describe the SASE phenomenon. The two-time correlation function is necessary for calculation of averaged SASE spectrum. The solution of the correlation function equation for linear stage of SASE process is obtained.

• N. Mahdizadeh
  Islamic Azad University, Sabzevar Branch, Sabzevar
• F.M. Aghamir
  University of Tehran, Tehran
• A. Raghavi
  pnum, Mashhad
• S. Saviz
  PPRC, Tehran

The effects of temperature on the growth rate of a two-stream free electron laser (TSFEL) with planar wiggler magnetic pump have been investigated. The dispersion equation has been derived through the use of continuity, momentum transfer, and Maxwell's equations. In the analysis, only the longitudinal component of the pressure tensor is considered in the electron equation of motion. The characteristics of the dispersion relation along with the growth rate are analyzed numerically. The results show that the growth rate in this system (TSFEL) is relatively higher than the conventional FEL; finally, we compare our results with other cases, like without beam temperature, and conventional FEL.

• W. Seidel, S. Winnerl
  FZD, Dresden

In order to decrease the average radiation power of the Rossendorf free-electron laser FELBE, as required for certain experiments (high pulse energies but moderate or low average power), the FEL repetition rate can be reduced from 13 MHz to 1 kHz. To this end, plasma switching of FEL radiation pulses was demonstrated for cw operation. The plasma switch is based on the principle of photo-induced reflectivity by an optically excited electron-hole plasma. Germanium or silicon serves as semiconductor material for the switch. The semiconductor was illuminated by a Nd:YAG laser amplifier system (1 kHz, wavelength {10}64 nm, pulse duration16 ps, 1Watt), generating an electron-hole plasma on the front surface of the semiconductor. To integrate this plasma-switch into the existing experimental set-up we build an additional by-pass to the Germanium or Silicon slab which is under Brewster’s angle. To get a high contrast in the switched beam we adjust the polarization plane of the incoming beam to the right direction by using an additional polarization rotator. We will report on first results at different wavelength. Submitted as a poster to the FEL 2010 conference.

• P. Stoltz, C. Nieter, C. Roark
  Tech-X, Boulder, Colorado
• J.D.A. Smith
  TXUK, Warrington

Multipacting is a potential limit on the power one can deliver to different components of an FEL source, including the power couplers and the electron source cathode. Simulation is a main tool in helping to understand and mitigate multipacting. We present recent work on benchmarking multipacting simulation, including comparison with other codes and with rectangular waveguide experiment.

• A. Marinelli, J.B. Rosenzweig
  UCLA, Los Angeles, California

Longitudinal space-charge forces can be a major source of micro-bunching instability. We will discuss a three-dimensional theoretical model for the high frequency limit of space-charge interactions leading to density modulation at the optical scale. Particular emphasis will be given to the effect of transverse thermal motion on the angular distribution of micro-bunching and to its connection to the physics of Landau damping in longitudinal plasma oscillations. A comparison with the results of high resolution molecular dynamics simulations will also be discussed.