Abstract
Crystal monochromators are often the primary optics in hard X-ray synchrotron beamlines. Management of power load is central to their design. Strict requirements on stability and deformation are to be met, as new-generation synchrotron sources deliver brighter beams of X-rays. This article sets out to illustrate an overall picture of the deformation caused by heat load in a cryo-cooled Si crystal monochromator using first principles. A theoretical model has been developed to predict the temperature distribution and surface deformation by applying intrinsic properties of Si material and the cooling system parameters. The model explains the universal behaviour of crystal slope error versus absorbed power; it has been benchmarked against experimental data and used to interpret finite-element analysis of cryogenically cooled crystals.
Highlights
Cryo-cooled silicon crystals have been used for decades as monochromators in hard X-ray synchrotron beamlines
Considerable increase of incident power P and power density Pd on monochromators is currently observed on some hard X-ray beamlines at Diamond Light Source (DLS), equipped with new higher-magnetic-field undulators
As the model has so far provided accuracy of order 10% to 20%, compared with Finite-element analysis (FEA) or experimental data at DLS, the final monochromator design should rely on FEA
Summary
Cryo-cooled silicon crystals have been used for decades as monochromators in hard X-ray synchrotron beamlines. Well designed cryo-cooling systems successfully minimize the surface deformation even under high power load from intense undulator sources. Ongoing upgrades of synchrotron photon sources require further improvements of optical components. The aim is to conserve the natural collimation and brightness of synchrotron beams in lower-emittance machines (Huang et al, 2014; Brumund et al, 2021; Zhang et al, 2013). Considerable increase of incident power P and power density Pd on monochromators is currently observed on some hard X-ray beamlines at Diamond Light Source (DLS), equipped with new higher-magnetic-field undulators. An optimized crystal cooling design will reduce optics deformations, prevent changes in diffracted beam wavefront and improve focusing
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