Author: Reiche, S.
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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.  
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TUP019 Time Locking Options for the Soft X-Ray Beamline of SwissFEL 388
  • E. Prat, S. Reiche
    PSI, Villigen PSI, Switzerland
  SwissFEL is an FEL facility presently under construction at the Paul Scherrer institute that will serve two beamlines: Aramis, a hard X-ray beamline which is in construction phase and will provide FEL radiation in 2017 with a wavelength between 0.1 and 0.7 nm; and Athos, a soft X-ray beamline which is in design phase and it is expected to offer FEL light in 2021 for radiation wavelengths between 0.7 and 7 nm. A passive synchronization of the FEL signal to a laser source is fundamental for key experiments at Athos, such as the time-resolved resonant inelastic X-ray scattering (RIXS) experiments. In this paper we explore different options to achieve this time synchronization by means of energy modulating the electron beam with an external laser.  
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TUP022 Measurement of Spatial Displacement of X-rays in Crystals for Self-Seeding Applications 405
  • A. Rodriguez-Fernandez, B. Pedrini, S. Reiche
    PSI, Villigen PSI, Switzerland
  • K. Finkelstein
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  Free-electron laser (FEL) radiation arises from shot noise in the electron bunch, which is amplified along the undulator section and results in X-ray pulses consisting of many longitudinal modes [1]. The output bandwidth of FELs can be decreased by seeding the FEL process with longitudinally coherent radiation. In the hard x-ray region, there are no suitable external sources. This obstacle can be overcome by self-seeding. The X-ray beam is separated from the electrons using a magnetic chicane, and then monochromatized. The monochromatized X-rays serve as a narrowband seed, after recombination with the electron bunch, along the downstream undulators. This scheme generates longitudinally coherent FEL pulses.[2] have proposed monochromatization based on Forward Bragg Diffraction (FBD), which introduces a delay of the narrowband X-rays pulse of the order of femtoseconds that can be matched to the delay of the electron bunch due to the chicane. Unfortunately, the FBD process produces a small transverse displacement of the X-ray beam, which results in the loss of efficiency of the seeding process [3]. Preliminary results from an experiment performed at Cornell High Energy Synchrotron Source seem to confirm the predicted transverse displacement, which is therefore to be taken into account in the design of self-seeding infrastructure for optimizing the FEL performance.
[1] J.S. Wark et al., J. Apply. Crystallogr. 32, 692 (1999)
[2] G. Geloni et al., DESY report 10-053 (2010).
[3] Y. Shvyd'ko et al., Phys. Rev. ST Accel. Beams 15, 100702 (2012)
poster icon Poster TUP022 [5.503 MB]  
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