Author: Fell, B.D.
Paper Title Page
THP059 The Laser Heater System of SwissFEL 871
  • M. Pedrozzi, M. Calvi, R. Ischebeck, S. Reiche, C. Vicario
    PSI, Villigen PSI, Switzerland
  • B.D. Fell, N. Thompson
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  Short wavelength FELs are generally driven by high-brilliance photo-cathode RF-guns which generate electron beams with an uncorrelated energy spread on the order of 1 keV or less. These extremely cold beams can easily develop micro-bunching instabilities caused by longitudinal space charge forces after the compression process. This can result in a blow up of the energy spread and emittance beyond the tolerable level for SASE emission. It has been demonstrated theoretically and experimentally [1] that a controlled increase of the uncorrelated energy spread to typically a few keV is sufficient to strongly reduce the instability growth. In the laser heater system, one achieves a controlled increase of the beam energy spread by a resonant interaction of the electron beam with a transversally polarized laser beam inside of an undulator magnet. The momentum modulation resulting from the energy exchange within the undulator is consequently smeared out in the transmission line downstream of the laser heater system. In SwissFEL, the laser heater system is located after the first two S-band accelerating structures at a beam energy of 150 MeV. This paper describes the layout and the sub-components of this system.
[1] Z. Huang, et al, Phys. Rev. Special Topics – Accelerator and beams 13, 020703 (2010)