Author: Ferrari, E.
Paper Title Page
Characterization of the Polarization of the First and Second Stage of FERMI FEL-2  
  • E. Roussel, E. Allaria, C. Callegari, M. Coreno, R. Cucini, S. Di Mitri, B. Diviacco, E. Ferrari, P. Finetti, D. Gauthier, L. Giannessi, G. Penco, L. Raimondi, C. Svetina, M. Zangrando
    Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
  • A. Beckmann
    XFEL. EU, Hamburg, Germany
  • L. Giannessi
    ENEA C.R. Frascati, Frascati (Roma), Italy
  • L. Glaser, G. Hartmann, F. Scholz, J. Seltmann, I. Shevchuk, J. Viefhaus
    DESY, Hamburg, Germany
  • M. Zangrando
    IOM-CNR, Trieste, Italy
  The FERMI free-electron laser (FEL) is nowadays the only user facility equipped with Apple-II type undulators that permit to produce either elliptical, circular or linearly polarized light within the extreme ultraviolet and soft x-ray wavelength range. The FERMI FEL-2 line is based on a two-stage "fresh-bunch" high-gain harmonic generation (HGHG) scheme, where the light emitted by a first HGHG stage seeds a fresh portion of the electron bunch in a second FEL stage. Both FEL lights, from the first and second stages, can be tuned separately to linear horizontal, vertical or circular left and right polarization. We report on a systematic characterization of the polarization state of the two stages of FERMI FEL-2 by using an electron Time-Of-Flight based polarimeter. Our results show a good independent control of the polarization of the two stages, with a high degree of polarization typically higher than 95%*
* E. Roussel et al., Polarization Characterization of Soft X-Ray Radiation at FERMI FEL-2. Photonics 2017, 4, 29.
TUP053 The ACHIP Experimental Chambers at PSI 1
  • E. Ferrari, M. Bednarzik, S. Bettoni, S. Borrelli, H.-H. Braun, M. Calvi, Ch. David, M.M. Dehler, F. Frei, T. Garvey, V. Guzenko, N. Hiller, R. Ischebeck, C. Ozkan Loch, E. Prat, J. Raabe, S. Reiche, L. Rivkin, A. Romann, B. Sarafinov, V. Schlott, S. Susmita
    PSI, Villigen PSI, Switzerland
  • E. Ferrari, L. Rivkin
    EPFL, Lausanne, Switzerland
  • P. Hommelhoff
    University of Erlangen-Nuremberg, Erlangen, Germany
  • J.C. McNeur
    Friedrich-Alexander Universität Erlangen-Nuernberg, University Erlangen-Nuernberg LFTE, Erlangen, Germany
  Funding: Gordon and Betty Moore Foundation
The Accelerator on a Chip International Program (ACHIP) is an international collaboration, funded by the Gordon and Betty Moore Foundation, whose goal is to demonstrate that a laser-driven accelerator on a chip can be integrated to fully build an accelerator based on dielectric structures. PSI will provide access to the high brightness electron beam of SwissFEL to test structures, approaches and methods towards achieving the final goal of the project. In this contribution, we will describe the two interaction chambers installed on SwissFEL to perform the proof-of-principle experiments. In particular, we will present the positioning system for the samples, the magnets needed to focus the beam to sub-micrometer dimensions and the diagnostics to measure beam properties at the interaction point.
Using the Optical-Klystron Effect to Increase and Measure the Intrinsic Beam Energy Spread in Free-Electron Laser Facilities  
  • E. Prat, S. Reiche, T. Schietinger
    PSI, Villigen PSI, Switzerland
  • E. Ferrari
    EPFL, Lausanne, Switzerland
  We present a setup based on the optical klystron concept consisting of two undulator modules separated by a magnetic chicane, that addresses two issues in free-electron laser (FEL) facilities. On the one hand, it allows an increase of the intrinsic energy spread of the beam at the source, which is useful to counteract the harmful microbunching instability. This represents an alternative method to the more conventional laser heater with the main advantage that no laser system is required. On the other hand, the setup can be used to reconstruct the initial beam energy spread, whose typical values in FEL injectors around 1 keV are very difficult to measure with standard procedures.  
High Energy Tunable THz Source Based on Wakefield Excitation  
  • S. Bettoni, P. Craievich, E. Ferrari, R. Ischebeck, F. Marcellini, C. Ozkan Loch, M. Pedrozzi, S. Reiche, V. Schlott
    PSI, Villigen PSI, Switzerland
  We plan to use the interaction of a beam optimized for the generation of FEL radiation with a dielectric waveguide as a pump source for pump and probe experiments in FEL facilities. This scheme provides several advantages to fulfill the user requirements for a radiation source, in particular synchronization with the hard x-ray pulses, tunability throughout the THz frequency range of interest and energy level. We present the optimization of this scheme for SwissFEL, where optimized beam optics matches into a small aperture dielectric waveguide allowing for the highest THz radiation energy. We also propose a method to further increase the THz radiation energy at higher frequencies by shaping the electron bunch.
Paper soon submittedto a journal
Passive Linearization of the Magnetic Bunch Compression Using Self-Induced Field and Without Any Active Higher Harmonic RF Structure  
  • G. Penco, E. Allaria, I. Cudin, S. Di Mitri, D. Gauthier, L. Giannessi, E. Roussel, S. Spampinati, M. Trovò
    Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
  • S. Bettoni, P. Craievich, E. Ferrari
    PSI, Villigen PSI, Switzerland
  • L. Giannessi
    ENEA C.R. Frascati, Frascati (Roma), Italy
  • E. Roussel
    SOLEIL, Gif-sur-Yvette, France
  In linac-driven free-electron lasers, colliders and energy recovery linacs, a common way to compress the electron bunch to kA level is based upon the implementation of a magnetic dispersive element that converts the bunch energy deviation in path-length difference. The non-linearities of such a process are usually compensated by enabling a high harmonic rf structure properly tuned in amplitude and phase. This approach is however not straightforward for foreseen C and X-band linacs. In this work we report the experiment performed on the FERMI linac that has demonstrated the possibility to exploit the longitudinal self-induced field excited by the electron beam itself to passively linearize the compression process without any active higher harmonic rf structure. In this novel configuration, the FERMI electron bunch was compressed up to 700 A as in the nominal case and driven along the FERMI FEL-1 undulators, generating intense extreme-ultraviolet pulses that were provided to users for experiments.  
Sub-Micrometer Resolution, Nanotechnology Based Wire Scanners for Beam Profile Measurements at SwissFEL  
  • S. Borrelli, M. Bednarzik, Ch. David, E. Ferrari, A. Gobbo, V. Guzenko, N. Hiller, R. Ischebeck, G.L. Orlandi, C. Ozkan Loch, B. Rippstein, V. Schlott
    PSI, Villigen PSI, Switzerland
  SwissFEL Wire scanners (WSCs) measure electron beam transverse profile and emittance with high-resolution in a minimally-invasive way. They consist of a wire fork equipped with two 5 micrometer W wires, for high-resolution measurements, and two 12.5 micrometer Al(99):Si(1) wires, to measure the beam profile during FEL operation. Although the SwissFEL WSCs resolution is sufficient for many purposes, for some machine operations and experimental applications it is necessary to improve it under micrometer scale. The WSC spatial resolution is limited by the wire width which is constrained to few micrometers by the conventional manufacturing technique of stretching a metallic wire onto a wire-fork. In this work, we propose to overcome this limitation using the nanofabrication of sub-micrometer metallic stripes on a membrane by means of e-beam lithography. This presentation focuses in the design, construction and characterization of a high-resolution WSC prototype consisting of a silicon nitride membrane onto which two gold or nickel wires, widths ranging from 2 micrometers to 0.4 micrometers, are electroplated. We will also present the preliminary electron beam tests of our prototype.  
Saturation of Scintillators in Profile Monitors  
  • R. Ischebeck, E. Ferrari, F. Frei, N. Hiller, G.L. Orlandi, C. Ozkan Loch, V. Schlott
    PSI, Villigen PSI, Switzerland
  SwissFEL uses scintillating screens to measure the transverse profile of the electron beam. These screens, in combination with quadrupole magnets and a transverse deflecting RF structure, are used to measure projected and slice emittance, as well as bunch length. Scintillating screens have been chosen over optical transition radiators because of the coherent transition radiation emitted by the compressed bunches. It is therefore instrumental to characterize the linearity of these monitors in order to ensure reliable measurements. We are presenting here a measurement of saturation effects due to the high charge density in SwissFEL, and describe the results with a numerical model of the process.