OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 3 2024 optical elements is the ability to dissipate the thermal load caused by the local impact of the “white” SR beam on the surface of the product (Fig. 5). In addition, the material should be resistant to radiation damage [3, 5] and meet radiation bandwidth requirements. Section “Monochromators based on multilayer structures” describes the materials used for producing X-ray mirrors of multilayer monochromators. When manufacturing crystalline monochromators, silicon and germanium crystals with the necessary thermal conductivity are most often used as elements providing diffraction of X-ray radiation [50]. This function can also be performed by diamonds. Diamond crystals are used at sources with high radiation flux characterized by increased thermal load. Nevertheless, in comparison with silicon and germanium, diamond, having excellent thermal conductivity, is characterized by lower values of the reflection coefficient [51], which limits the practical application of this material. The optical element (monochromator crystal, X-ray mirror) that perceives the main thermal load is subject to deformation accompanied by changes in its shape. To maintain parallelism of working surfaces of crystal pairs (and X-ray mirrors), and, consequently, to ensure the functionality of the device, forced cooling of heat-loaded elements is used. Depending on the amount of heat released per unit volume of material, the type of cooling is selected (water or cryogenic), as well as the method of cooling (direct or indirect). Problems related to crystal cooling are among the most important when designing monochromators [5]. The peculiarities of the technical solutions used by the developers determine the accuracy of the devices. Several variants of monochromators with different approaches to the problem of cooling of optical elements are given below. One of them consists of using cooling channels (Fig. 26) laid directly in the monochromator crystals [52]. Fig. 26. Schematic of the crystal with direct cooling. According to [52] Fig. 25. Configuration of mirrors of the focusing monochromator. According to [48]
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