Thermal deformations in a high flux beam position monitor

Beam position monitors in three of the X-ray beam lines at the National Synchrotron Light Source employ a pair of metal blades at predetermined gaps. The thin blades intercept the fringes of the photon beam and generate an electrical signal which determines the relative beam position. The beam power deposited on the blades is removed by heat pipes to a heat exchanger outside the vacuum vessel. In this paper, we present results from nonlinear finite element analyses to describe temperature and deformation fields in a position monitor blade subassembly designed for a high flux soft X-ray beam line. These analyses show that, for the worst case of beam exposure, one of the blades would be subjected to high temperature gradients. The resulting thermal stresses can then exceed the temperature-dependent yield stress of the blade material, causing substantial plastic deformations. We compare the analysis results for two different blade materials, namely, tungsten, and a molybdenum alloy (TZM). (orig.)