Large-area Kapton x-ray windows

Some X-ray instruments require the utilization of large-area windows to provide vacuum barriers. The necessary attributes of the window material include transparency to X-rays, low scattering, and possession of suitable mechanical properties for reliable long-term performance. Kapton is one such material except that it is a polymer and a large window made from Kapton with a pressure differential of one atmosphere across it can undergo substantial deformation at room temperature. In this paper, we report on the mechanical testing of Kapton samples including creep measurements, and comparison with published data. We use of these data together with analytical / numerical models to predict the changes in the profile of Kapton vacuum windows over time, and show good agreement with experimental measurements.