Cheng Xianchao, Zhang Lin, Morawe Christian, Sanchez Del Rio Manuel
European Synchrotron Radiation Facility, 71 avenue des Martyrs, 38000 Grenoble, France.
J Synchrotron Radiat. 2015 Mar;22(2):317-27. doi: 10.1107/S1600577514026009. Epub 2015 Jan 28.
Multilayer optics for X-rays typically consist of hundreds of periods of two types of alternating sub-layers which are coated on a silicon substrate. The thickness of the coating is well below 1 µm (tens or hundreds of nanometers). The high aspect ratio (∼10(7)) between the size of the optics and the thickness of the multilayer can lead to a huge number of elements (∼10(16)) for the numerical simulation (by finite-element analysis using ANSYS code). In this work, the finite-element model for thermal-structural analysis of multilayer optics has been implemented using the ANSYS layer-functioned elements. The number of meshed elements is considerably reduced and the number of sub-layers feasible for the present computers is increased significantly. Based on this technique, single-layer coated mirrors and multilayer monochromators cooled by water or liquid nitrogen are studied with typical parameters of heat-load, cooling and geometry. The effects of cooling-down of the optics and heating of the X-ray beam are described. It is shown that the influences from the coating on temperature and deformation are negligible. However, large stresses are induced in the layers due to the different thermal expansion coefficients between the layer and the substrate materials, which is the critical issue for the survival of the optics. This is particularly true for the liquid-nitrogen cooling condition. The material properties of thin multilayer films are applied in the simulation to predict the layer thermal stresses with more precision.
用于X射线的多层光学器件通常由数百个周期的两种交替子层组成，这些子层涂覆在硅衬底上。涂层厚度远低于1微米（几十或几百纳米）。光学器件尺寸与多层膜厚度之间的高纵横比（约10(7)）会导致数值模拟（使用ANSYS代码进行有限元分析）的元素数量巨大（约10(16)）。在这项工作中，使用ANSYS层功能单元实现了多层光学器件热结构分析的有限元模型。网格单元数量大幅减少，当前计算机可行的子层数显著增加。基于该技术，研究了用水或液氮冷却的单层镀膜镜和多层单色仪，给出了热负载、冷却和几何形状的典型参数。描述了光学器件冷却和X射线束加热的影响。结果表明，涂层对温度和变形的影响可忽略不计。然而，由于层与衬底材料之间不同的热膨胀系数，层中会产生较大应力，这是光学器件能否存活的关键问题。在液氮冷却条件下尤其如此。在模拟中应用了多层薄膜的材料特性，以更精确地预测层热应力。
