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Description
Cavity-based x-ray free-electron lasers (CBXFEL) will allow use of
optical cavity feedback to support generation of fully coherent x-rays
of high brilliance and stability by electrons in undulators. CBXFEL
optical cavities comprise Bragg-reflecting flat crystal mirrors, which
ensure x-rays circulation on a closed orbit, and x-ray refractive
lenses, which stabilize the orbit and refocus the x-rays back on the
electrons in the undulator. Depending on the cavity design, there are
tens of degrees of freedom of the optical elements, which can never be
perfectly aligned. Here [1], we study signatures of misalignment of the
optical components and of the undulator source with the purposes of
understanding the effects of misalignment on x-ray beam dynamics,
understanding misalignment tolerances, and developing cavity alignment
procedures. Betatron oscillations of the x-ray beam trajectory are
one of the characteristic signatures of cavity misalignment. The
oscillation period is in the general case a non-integer number of
round-trip passes of x-rays in the cavity. This period (unlike the
amplitude and offset of the oscillations) is independent of the type
of misalignment and is defined by cavity parameters. The studies are
performed on an example of a four-crystal rectangular cavity [2] using
analytical and numerical wave optics as well as ray-tracing
techniques.
References:
[1]. Peng Qi and Yuri Shvyd'ko, Phys. Rev. Accel. Beams, 25 (2022) 050701
[2]. G. Marcus, et al., CBXFEL R&D: A Joint Argonne National Laboratory and SLAC National Laboratory Collaboration, FEL2019, doi:10.18429/JACoW-FEL2019-TUD04
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