OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 3 2024 detail. In [20] the dispersive crystal arrangement corresponding to Fig. 11 b is used. Work [21] presents a configuration similar to the scheme corresponding to Fig. 11 d. Asymmetric reflection of rays takes place in both cases. Devices providing more than two reflections on the crystals can be used to improve the monochromaticity of the radiation. In [21–23] monochromators with two and three pairs of crystals (four and six reflections), each of which emits a certain spectral band, are presented. Devices of this type, having improved monochromaticity indices, make it possible to preserve the beamaxis from the entrance to themonochromator to its exit. In some cases, the fulfillment of this condition is important in designing synchrotron radiation stations [24, 25]. Most monochromators installed on SRS are equipped with two-crystal nodes [26]. One of the most common designs of crystal monochromators involves using channel-cut crystals. In this case, both plates of the monochromator belong to the same monocrystalline block. In the Russian-language literature, the structures made according to this scheme (Fig. 12) are called “butterfly” [27]; in the English version these are called channel-cut monochromator (CCM). Fig. 12. The working element of the channel-cut monochromator. Two faces of the crystal, on which the beam reflection occurs, belong to a single monocrystal [28] In contrast to two-crystal monochromators, when using the channel-cut monochromator scheme, the crystal is cut out of the monoblock in such a way that its reflecting surfaces are located on the inner sides of the channel (Fig. 12) [28–29]. The main advantage of such a technical solution is the possibility of ensuring perfect parallelism of the reflecting surfaces at the stage of crystal formation. A significant violation of parallelism of the working surfaces of the channel-cut monochromator due to thermal deformation of the material is observed at high radiation energies (over 20 keV [3, p. 152]). When using monochromators with independent crystals that have several degrees of freedom difficulties in parallelism of its working surfaces are possible [28]. Fig. 13 b [30] presents one of the varieties of dispersive monochromators with channel-cut, providing fourfold reflection of X-rays [21, 22, 30, 31]. In [32] a scheme of a channel-cut monocrystal with three diffracting faces as working surfaces is demonstrated (Fig. 14). a b Fig. 13. Monochromator with channel-cut: β – angle of inclination of the facet [30]
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