Device for source position stabilization and beam parameter monitoring at inverse Compton X-ray sources.

Benedikt Günther,Franz Pfeiffer,Martin Dierolf,Klaus Achterhold

doi:10.1107/s1600577519006453

Benedikt Günther, Franz Pfeiffer + Show 2 more

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https://doi.org/10.1107/s1600577519006453

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Abstract

Compact X-ray sources based on inverse Compton scattering provide brilliant and partially coherent X-rays in a laboratory environment. The cross section for inverse Compton scattering is very small, requiring high-power laser systems as well as small laser and electron beam sizes at the interaction point to generate sufficient flux. Therefore, these systems are very sensitive to distortions which change the overlap between the two beams. In order to monitor X-ray source position, size and flux in parallel to experiments, the beam-position monitor proposed here comprises a small knife edge whose image is acquired with an X-ray camera specifically designed to intercept only a very small fraction of the X-ray beam. Based on the source position drift recorded with the monitor, a closed-loop feedback stabilizes the X-ray source position by adjusting the laser beam trajectory. A decrease of long-term source position drifts by more than one order of magnitude is demonstrated with this device. Consequently, such a closed-loop feedback system which enables stabilization of source position drifts and flux of inverse Compton sources in parallel to experiments has a significant impact on the performance of these sources.

Highlights

Based on the source position drift recorded with the monitor, a closed-loop feedback stabilizes the X-ray source position by adjusting the laser beam trajectory
In order to suppress this behavior, we developed a closed-loop X-ray beam-position monitor and stabilization system that is designed to work in parallel to experiments
It has been demonstrated here that a beam-position monitor consisting of a knife edge and a customized commercial CCD camera is

Summary

Introduction

High-brilliance X-rays generated in synchrotron facilities are necessary for a wide range of advanced methods in imaging, e.g. phase contrast imaging (Bonse & Hart, 1965; Snigirev et al, 1995; Cloetens et al, 1996; Momose et al, 2003; Weitkamp et al, 2005), real-time or high-speed imaging (Berg et al, 2013; Maire et al, 2016; Olbinado et al, 2017) as well as high-resolution imaging (Sakdinawat & Attwood, 2010), spectroscopy, e.g. extended X-ray absorption fine structure (Lee et al, 1981), or X-ray polarimetry, e.g. circular magnetic dichroism (Schutz et al, 1987; Chen et al, 1995). Steering of the laser beam can be compromised by thermally induced stress in optics, e.g. if those components are placed in close proximity to strong conventional magnets, especially during the magnets’ heat-up This changes electron beam and/or laser beam position and degrades overlap between these two beams, resulting in a reduced X-ray flux, as well as a shift of the source position. This resulted in stronger shifts of the X-ray source position leading to a degraded X-ray flux (cf. Fig. 4b), as discussed above

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