Physical Review Special Topics. Accelerators and Beams (Oct 2014)

Design and application of multimegawatt X-band deflectors for femtosecond electron beam diagnostics

  • Valery A. Dolgashev,
  • Gordon Bowden,
  • Yuantao Ding,
  • Paul Emma,
  • Patrick Krejcik,
  • James Lewandowski,
  • Cecile Limborg,
  • Michael Litos,
  • Juwen Wang,
  • Dao Xiang

DOI
https://doi.org/10.1103/PhysRevSTAB.17.102801
Journal volume & issue
Vol. 17, no. 10
p. 102801

Abstract

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Performance of the x-ray free electron laser Linac Coherent Light Source (LCLS) and the Facility for Advanced Accelerator Experimental Tests (FACET) is determined by the properties of their extremely short electron bunches. Multi-GeV electron bunches in both LCLS and FACET are less than 100 fs long. Optimization of beam properties and understanding of free-electron laser operation require electron beam diagnostics with time resolution of about 10 fs. We designed, built and commissioned a set of high frequency X-band deflectors which can measure the beam longitudinal space charge distribution and slice energy spread to better than 10 fs resolution at full LCLS energy (14 GeV), and with 70 fs resolution at full FACET energy (20 GeV). Use of high frequency and high gradient in these devices allows them to reach unprecedented performance. We report on the physics motivation, design considerations, operational configuration, cold tests, and typical results of the X-band deflector systems currently in use at SLAC.