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McNeil, B.W.J.

Paper Title Page
TUPE049 Optimisation of an HHG-Seeded Harmonic Cascade FEL Design for the NLS Project 2254
 
  • D.J. Dunning, N. Thompson
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
  • R. Bartolini
    JAI, Oxford
  • H. Geng, Z. Huang
    SLAC, Menlo Park, California
  • B.W.J. McNeil
    USTRAT/SUPA, Glasgow
  
 

Optimisation studies of an HHG-seeded harmonic cascade FEL design for the UK's proposed New Light Source (NLS) facility are presented. Three separate FELs are planned to meet the requirements for continuous coverage of the photon energy range 50-1000 eV with variable polarisation, 20 fs pulse widths and good temporal coherence. The design uses an HHG seed source tuneable from 50-100 eV to provide direct FEL seeding in this range, and one or two stage harmonic cascades to reach the higher photon energies. Studies have been carried out to optimise a harmonic cascade FEL operating at 1 keV; topics investigated include modulator configuration, seed power level and effects of the HHG seed structure. FEL simulations using realistic electron beam distributions are presented and tolerance to increased emittance has been considered.

  
TUPE050 Improved Temporal Coherence in SASE FELs 2257
 
  • N. Thompson, D.J. Dunning
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
  • B.W.J. McNeil
    USTRAT/SUPA, Glasgow
  • N. Thompson
    Cockcroft Institute, Warrington, Cheshire
  
 

A scheme for the generation of attosecond pulse trains in FEL amplifiers was recently proposed*. The method uses repeated equal temporal delays between the electron bunch and co-propagating radiation to generate a modal structure in the radiation field. The modes may be phase-locked via an energy modulation in the electron beam. As a consequence of the radiation /electron delays, the relative radiation /electron slippage during the interaction is increased and leads to a longer cooperation length with the effect of improving the temporal coherence. In this paper we present simulations demonstrating this effect. In particular, we show that the average spacing between the temporal spikes in a SASE FEL is increased in proportion to the increase in the cooperation length. It may therefore be possible to operate a SASE FEL in single-spike mode with longer, higher charge, electron bunches than previously thought possible.


* Physical Review Letters 100, (203901) 2008.