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Thermal, structural, and diffraction analysis of a gallium-cooled x-ray monochromator

The next generation of synchrotron radiation sources will produce very high power and power density x-ray beams. For example, the Advanced Photon Source (APS) under construction at Argonne National Laboratory will produce beams containing up to 5 kW of power and peak normal power densities in excess of 150 W/mm2. Normally, the first optical component to intercept the x-ray beam is a crystal monochromator. This device typically uses a single crystal of silicon or germanium as a band-pass filter according to Braggs' law of diffraction. Under the severe heat loading of modern synchrotron beams, the performance of the monochromator is degraded by reducing the photon throughput and increasing the beam divergence. This paper describes the methods used to calculate the thermally induced deformations in standardly configured monochromator crystals using finite element analysis. The results of these analyses are compared to recent experiments conducted at the Cornell High Energy Synchrotron Source (CHESS) using a high-performance, gallium-cooled crystal. Computer simulations can be used to evaluate the performance of high-heat-load x-ray optics for future synchrotron sources.