Brumund Philipp, Reyes-Herrera Juan, Detlefs Carsten, Morawe Christian, Sanchez Del Rio Manuel, Chumakov Aleksandr I
ESRF - The European Synchrotron, 38043 Grenoble Cedex 9, France.
J Synchrotron Radiat. 2021 Jan 1;28(Pt 1):91-103. doi: 10.1107/S1600577520014009.
The performance of a liquid-nitrogen-cooled high-heat-load monochromator with a horizontal scattering plane has been analysed, aiming to preserve the high quality of the X-ray beam in the vertical plane for downstream optics. Using finite-element analysis, height profiles of the crystal surface for various heat loads and the corresponding slope errors in the meridional and sagittal planes were calculated. Then the angular distortions of the reflected beam in both meridional and sagittal planes were calculated analytically and also modelled by ray tracing, revealing a good agreement of the two approaches. The results show that with increasing heat load in the crystal the slope errors of the crystal surface reach their smallest values first in the sagittal and then in the meridional plane. For the considered case of interest at a photon energy of 14.412 keV and the Si(111) reflection with a Bragg angle of 7.88°, the angular distortions of the reflected beam in the sagittal plane are an order of magnitude smaller than in the meridional one. Furthermore, they are smaller than the typical angular size of the beam source at the monochromator position. For a high-heat-load monochromator operating in the horizontal scattering plane, the sagittal angular distortions of the reflected beam appear in the vertical plane. Thus, such an instrument perfectly preserves the high quality of the X-ray beam in the vertical plane for downstream optics. Compared with vertical scattering, the throughput of the monochromatic beam with the horizontal scattering plane is reduced by only 3.3% for the new EBS source, instead of 34.3% for the old ESRF-1 machine. This identifies the horizontal-scattering high-heat-load monochromator as a device essentially free of the heat-load effects in the vertical plane and without significant loss in terms of throughput.
对具有水平散射平面的液氮冷却高热负荷单色仪的性能进行了分析，目的是为下游光学元件保持垂直平面内X射线束的高质量。使用有限元分析，计算了各种热负荷下晶体表面的高度轮廓以及子午面和弧矢面中的相应斜率误差。然后通过解析计算并利用光线追迹对子午面和弧矢面中反射光束的角度畸变进行了建模，结果表明两种方法吻合良好。结果表明，随着晶体热负荷的增加，晶体表面的斜率误差首先在弧矢面达到最小值，然后在子午面达到最小值。对于所考虑的感兴趣的情况，在光子能量为14.412 keV且布拉格角为7.88°的Si(111)反射时，反射光束在弧矢面的角度畸变比在子午面小一个数量级。此外，它们比单色仪位置处光束源的典型角度尺寸小。对于在水平散射平面中运行的高热负荷单色仪，反射光束的弧矢角畸变出现在垂直平面中。因此，这种仪器能完美地为下游光学元件保持垂直平面内X射线束的高质量。与垂直散射相比，对于新的EBS源，具有水平散射平面的单色光束的通量仅降低3.3%，而对于旧的ESRF-1机器则为34.3%。这表明水平散射高热负荷单色仪是一种在垂直平面内基本不受热负荷影响且通量无显著损失的装置。
