The paper presents the results of a study of the thermal loads of materials used in the production of x-ray optics. The development of new types of x-ray studies and the transition to the fourth generation of synchrotron radiation sources, which is realized by reducing the emittance of undulator sections, requires advanced studies of the thermal stability of the first components of the optical line of the beam. An increase in the radiation power density is a critical problem for the design of the optical elements of the undulator section; this is especially important for crystalline monochromators with relatively high angles of incidence. However, other optical elements — windows, lenses, slits, and zoom — are exposed to thermal loads. Therefore, it is important to consider the effect of thermal loads on materials of adaptive x-ray optics to predict not only cooling modes, but also thermal deformations. To this end, studies have been conducted on the interaction of X-rays with the main materials used in the production of X-ray optics - aluminum, beryllium, diamond and UHMW (ultra high molecular weight polyethylene).
The occurrence of thermal gradients occurs due to the absorption of X-rays by the surface of the material (radiant heat transfer) and volume absorption (according to the Burer-Lambert law). The problem was solved numerically by the finite element method in the ANSYS Workbench software package. In the framework of the task, the heat flux arising from the interaction of X-ray radiation with the surface of the substance was set as the boundary condition of heat transfer of the second kind. The shape of the heat spot was chosen in the form of a circle with a Gaussian character distribution of the density of thermal radiation. The interaction of X-rays with a plate of finite size and thickness was considered. As part of the problem statement, 3 loading modes with a characteristic X-ray wavelength were selected: 1, 0.5, and 0.25 angstroms.
The results of the calculations showed that the use of UHMW as a material for x-ray optics requires a very careful selection of operating modes, preference should be given to modes with a very low power density of the radiation load. The main heat load is associated with the surface absorption capacity of the material, combined with low thermal conductivity, leading to the appearance of a surface heat source that can literally burn through the material.
The best calculated thermal stability results were shown by diamond plates. In addition to excellent thermal conductivity, diamond has a low coefficient of volume attenuation of intensity, leading to low temperature gradients of the established temperature regime.
This research was supported by the by Russian Science Foundation (Project No. 19-72-30009) and the Russian Academic Excellence Project at the Immanuel Kant Baltic Federal University