LUX - a recirculating linac-based facility for ultrafast X-ray science
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Open Access Publications from the University of California

LUX - a recirculating linac-based facility for ultrafast X-ray science

  • Author(s): Corlett, J.N.
  • Barletta, W.A.
  • DeSantis, S.
  • Doolittle, L.
  • Fawley, W.M.
  • Heimann, P.
  • Leone, S.
  • Lidia, S.
  • Li, D.
  • Penn, G.
  • Ratti, A.
  • Reinsch, M.
  • Schoenlein, R.
  • Staples, J.
  • Stover, G.
  • Virostek, S.
  • Wan, W.
  • Wells, R.
  • Wilcox, R.
  • Wolski, A.
  • Wurtele, J.
  • Zholents, A.
  • et al.

We present recent developments in design concepts for LUX - a source of ultra-short synchrotron radiation pulses based on a recirculating superconducting linac. The source produces high-flux x-ray pulses with duration of 100 fs or less at a 10 kHz repetition rate, optimized for the study of ultra-fast dynamics across many fields of science [1]. Cascaded harmonic generation in free-electron lasers (FEL's) produces coherent radiation in the VUV-soft x-ray regime, and a specialized technique is used to compress spontaneous emission for ultra-short-pulse photon production in the 1-10 keV range. High-brightness electron bunches of 2-3 mm-mrad emittance at 1 nC charge in 30 ps duration are produced in an rf photocathode gun and compressed to 3 ps duration following an injector linac, and recirculated three times through a 1 GeV main linac. In each return path, independently tunable harmonic cascades are inserted to produce seeded FEL radiation in selected photon energy ranges from approximately 20 eV with a single stage of harmonic generation, to 1 keV with a four-stage cascade. The lattice is designed to minimize emittance growth from effects such as coherent synchrotron radiation (CSR), and resistive wall wakefields. Timing jitter between pump lasers and x-ray pulses is minimized by use of a stable optical master oscillator, distributing timing signals over actively stabilized fiber-optic, phase-locking all lasers to the master oscillator, and generating all rf signals from the master oscillator. We describe technical developments including techniques for minimizing power dissipation in a high repetition rate rf photocathode gun, beam dynamics in two injector configurations, independently tunable beamlines for VUV and soft x-ray production by cascaded harmonic generation, a fast kicker design, timing systems for providing synchronization between experimental pump lasers and the x-ray pulse, and beamline design for maintaining nm-scale density modulation.

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