Author: Bettoni, S.
Paper Title Page
Low Slice Emittance Preservation in Bunch Compressors  
  • S. Bettoni, M. Aiba, M. Pedrozzi, E. Prat, S. Reiche, T. Schietinger
    PSI, Villigen PSI, Switzerland
  • B. Beutner
    DESY, Hamburg, Germany
  Minimize the dilution of the beam emittance is crucial for accelerators, and in particular for Free Electron Lasers, where the length of the machine and the finally the efficiency of the lasing process depend on it. At the SwissFEL Injector Test Facility we measured unexpected slice emittance increase after compressing the bunch also for moderate compression factors. We experimentally characterized the dependency of this phenomenon on the beam and machine parameters relevant for the compression. In order to qualitatively reproduce all the measurements outcomes it was necessary to use a 3D beam dynamic model along the bunch compressor including coherent synchrotron radiation. After excluding space charge forces, spurious dispersion and microbunching instability as possible sources for the observed emittance dilution, we identified the coherent synchrotron radiation and its interaction with the electron beam as the main responsible of the phenomenon. We also studied both experimentally and with simulations the contribution of the mismatch along the bunch to the longitudinal variations of the slice emittance. These experimental and theoretical investigations allowed a re-optimization of the injector. Typically with 150 A peak current, 200 pC charge it was possible to reach less than 200 nm.rad for the central slice with a moderate increase up to less than 300 nm.rad on the tails.  
slides icon Slides TUC03 [1.395 MB]  
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