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Nuhn, H.-D.

Paper Title Page
RPPT035 Optimization of the LCLS X-Rray FEL Output Performance in the Presence of Strong Undulator Wakefields 2396
 
  • S. Reiche
    UCLA, Los Angeles, California
  • K.L.F. Bane, P. Emma, Z. Huang, H.-D. Nuhn, G.V. Stupakov
    SLAC, Menlo Park, California
  • W.M. Fawley
    LBNL, Berkeley, California
  
  Funding: The work was supported by the DOE Contract No. DE-AC02-76SF00515.

The Linac Coherent Light Source (LCLS) Free-Electron Laser will operate in the wavelength range of 1.5 to 15 Angstroms. Energy loss due to wakefields within the long undulator can degrade the FEL process by detuning the resonant FEL frequency. The wakefields arise from the vacuum chamber wall resistivity, its surface roughness, and abrupt changes in its aperture. For LCLS parameters, the resistive component is the most critical and depends upon the chamber material (e.g. Cu) and its radius. To study the expected performance in the presence of these wakefields, we make a series of "start-to-end" simulations with tracking codes PARMELA and ELEGANT and time-dependent FEL simulation codes Genesis 1.3 and Ginger. We discuss the impact of the wakefield on output energy, spectral bandwidth, and temporal envelope of the output FEL pulse, as well as the benefits of a partial compensation obtained with a slight z dependent taper in the undulator field. We compare these results to those obtained by decreasing the bunch charge or increasing the vacuum chamber radius. We also compare our results to those predicted in concurrent analytical work.