Author: Craievich, P.
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.  
RF Design of a C-Band Transverse Deflecting Structure for Femtosecond Scale Phase Space Measurements  
  • J.-Y. Raguin, P. Craievich
    PSI, Villigen PSI, Switzerland
  The RF design of a two-meter long C-band travelling-wave transverse deflecting structure for the bunch length and slice emittance diagnostics of electron bunches with an energy of several GeV is presented. The structure is of the constant-impedance type with cup-like cells, each of which incorporates two azimuthally symmetric caved-in walls to stabilize the polarized dipolar HEM11 modes. It operates with a 2π/3 phase advance per cell on the lowest first backward space harmonic of one of these HEM11 modes, the two lowest passbands of which are well separated in frequency to avoid mode mixing. With a 14 mm diameter iris aperture and a transverse impedance of the structure of around 43 MΩ/m, an integrated deflecting voltage of 35 MV is guaranteed with an input power lower than 25 MW. The topology of the identical input and output single-feed RF couplers is such that peak field values are well below the safe limit. Two structures with such a design meet the SwissFEL high-energy beam diagnostic requirements.