Author: Pedrozzi, M.
Paper Title Page
Temporal Profile Reconstruction Based on a Passive Streaker  
  • S. Bettoni, P. Craievich, M. Pedrozzi
    PSI, Villigen PSI, Switzerland
  A time resolved measurement of the beam is important to optimize the final performances of an accelerator and in particular it is crucial for Free Electron Lasers. A transverse deflecting cavity, as an iris loaded wave guide or multi cell-standing wave structures, is conventionally used to image the longitudinal profile of a streaked beam on a downstream screen. In this paper we present an alternative method to passively deflect the electron bunch by using the dipole wakefield excited by the electron bunch passing off-axis through a dielectric-lined or a corrugated pipe. Measurements of a proof-of-principle experiment performed at the SwissFEL Injector Test Facility compared with the simulations are also discussed here.  
THP049 High Power RF Test and Analysis of Dark Current in the SwissFEL-gun 843
  • P. Craievich, S. Bettoni, M. Bopp, A. Citterio, C. Ozkan, M. Pedrozzi, J.-Y. Raguin, M. Schaer, A. Scherer, T. Schietinger, L. Stingelin
    PSI, Villigen PSI, Switzerland
  To fulfill the beam quality and operational requirements of the SwissFEL project, currently under construction at the Paul Scherrer Institut, a new RF photocathode gun for the electron source was designed and manufactured in house. A 2.6 cell S-band gun operating with near-perfect rotationally symmetric RF field was designed to operate with a 100MV/m cathode field at a repetition rate of 100Hz with average power dissipation of 0.9kW with pulse duration of 1us. The first SwissFEL-gun is now fabricated and installed in the SwissFEL Injector Test Facility (SITF). The frequency spectrum and field balance, through bead-pulling, have been directly verified in-situ and then the gun has been operated with high-power RF. The results of bead-pull measurements and high-power tests are presented and discussed. In addition the emitted dark current was also measured during the high-power tests and the charge within the RF pulse was measured as a function of the peak cathode field at different pulse durations. Faraday cup data were taken for cathode peak RF fields up to 100MV/m for the case of a diamond-turned polycrystalline copper cathode.  
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)