Author: Thompson, N.
Paper Title Page
MOP061 Electron Beam Delays for Improved Temporal Coherence and Short Pulse Generation at SwissFEL 181
  • N. Thompson
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  • S. Reiche
    PSI, Villigen PSI, Switzerland
  Proposals have been made for the introduction of magnetic electron beam delays in between the undulator modules of a long sectional FEL undulator - these can be used for the generation of trains of FEL pulses which can individually be shorter than the FEL cooperation time [*] or to greatly improve the temporal coherence of the FEL output compared to the nominal SASE configuration [**,***,***]. This paper comprises a feasibility study of the application of these techniques to the SwissFEL hard X-Ray beamline. Three-dimensional simulations are used to investigate the potential photon output.
[*] N.R. Thompson and B.W.J. McNeil, PRL 100:203901, 2008.
[**] N.R. Thompson et al. In Proc IPAC2010, pages 2257–2259, 2010
[***] J. Wu, A. Marinelli, and C. Pellegrini. Proc FEL2012, 2012.
TUB01 Review of Coherent SASE Schemes 327
  • B.W.J. MᶜNeil, L.T. Campbell, J. Henderson
    USTRAT/SUPA, Glasgow, United Kingdom
  • D.J. Dunning, N. Thompson
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  Funding: We acknowledge STFC Agreement No. 4163192; ARCHIE-WeSt HPC, EPSRC grant EP/K000586/1; John von Neumann Institute for Computing (NIC) on JUROPA at Julich Supercomputing Centre (JSC), project HHH20
A review is presented of some of the methods and their origins that have recently been proposed to improve the temporal coherence of SASE output. These methods do not require any external laser seed field, or the use of the so-called self-seeding methods, where the SASE radiation is optically filtered and improved at an early stage of the interaction before re-injection and amplification to saturation. By using methods that introduce an additional relative propagation between the electron beam and the radiation field, the localised collective interaction, which leads to the formation of the ‘spiking’ associated with normal SASE output, is removed. The result is output pulses which are close to the fourier transform limit without the need for any external seeds or intermediate optics.
slides icon Slides TUB01 [6.256 MB]  
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)