Physical Review Accelerators and Beams (Mar 2024)

Microbunch rotation in an x-ray free-electron laser using a first-order achromatic bend

  • Rachel A. Margraf,
  • James P. MacArthur,
  • Gabriel Marcus,
  • Heinz-Dieter Nuhn,
  • Alberto Lutman,
  • Aliaksei Halavanau,
  • Zhen Zhang,
  • Zhirong Huang

DOI
https://doi.org/10.1103/PhysRevAccelBeams.27.030702
Journal volume & issue
Vol. 27, no. 3
p. 030702

Abstract

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Electrons in an x-ray free electron laser (XFEL) develop periodic density fluctuations, known as microbunches, which enable the exponential gain of x-ray power in an XFEL. When an electron beam microbunched at a hard x-ray wavelength is kicked, microbunches are often washed out due to the dispersion and R_{56} of the bend. An achromatic (dispersion-free) bend with a small R_{56}, however, can preserve microbunches, which rotate to follow the new trajectory of the electron bunch. Rotated microbunches can subsequently interact in a repointed undulator to produce a new beam of off-axis x rays. In this work, we demonstrate hard x-ray multiplexing in the Linac Coherent Light Source hard x-ray undulator line using microbunch rotation through a 10 μrad first-order-achromatic bend created by transversely offsetting quadrupole magnets in the FODO lattice. Quadrupole offsets are determined analytically from beam-matrix theory. We also discuss the application of microbunch rotation to out-coupling a cavity-based XFEL.