X-ray telescope mirror mounting and deformation reduction using ThermoYield actuators and mirror geometry changes

Recently, the X-ray optics community has been developing technology for high angular resolution, large collecting area X-ray telescopes such as the Lynx mission concept. To meet the high collecting area requirements of such telescope concepts, research is being conducted on thin, segmented optics. The precision mounting posts that fixture and align segmented optics must be the correct length to sub-micron accuracy to satisfy the angular resolution goals of such a concept. Mirror distortion caused by adhesive shrinkage at mount points on the mirror surface also needs to be controlled to micron-radian tolerances. We report on two solutions to these problems. Set-and-forget adjustable length optical mounting posts have been developed to control mirror spacer length. The actuator consists of a metal cylinder with a cylindrical neck cut halfway along the length. To change the length of this actuator, an axial force is applied and the neck is momentarily heated to the plastic deformation temperature via resistive heating. All of the plastic deformation that occurs becomes permanent after cooling. Both compression and expansion of these actuators has been demonstrated in steps ranging from 6 nm to several microns. This paper will describe an experimental setup, show, and discuss data. Additionally, a stress relief technique to reduce mirror distortion caused by shrinkage of the adhesive bond to the actuator is proposed and demonstrated by modelling.