Enhancing the Athena Telescope Performance Using X-Ray Mirror Coatings

Research output: Book/ReportPh.D. thesis

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Abstract

The Athena (Advanced Telescope for High Energy Astrophysics) mission is a next generation X- ray observatory selected by the European Space Agency. Expected for launch in the early 2030s, Athena will define the next era of X-ray astronomy with an unprecedented performance in the 0.1 − 12 keV range. The focusing optics of Athena is based on silicon pore optics (SPO) technology with mirror sur- faces coated with X-ray reflective thin films. DTU Space is leading the research and development on state-of-the-art thin film coatings suitable to achieve the Athena performance requirements. This thesis presents the investigation of a new candidate thin film bilayer coating comprised of iridium and silicon carbide. The thin films are characterized in terms of stability of performance, surface evolution and chemical composition. The silicon carbide overlayer is essential to achieve the required low-energy performance of Athena. However, the industrialization processes required to manufacture more than 100,000 SPO mirror plates for the flight optics, including chemical and thermal exposure, may challenge the integrity of the low-density overcoat. Demonstrating compatibility of the thin film with all process parameters is therefore critical to qualify the material combination. In this work, the iridium and silicon carbide bilayer coating design is demonstrated to be a suitable candidate for the Athena optics. Exposing the coatings to a chemical process step required for the SPO plate stacking emphasizes a critical issue since preliminary results indicate partial removal of the silicon carbide overcoat. Future studies should investigate the relevant process parameters in order to eliminate risks to the low-energy performance of Athena. Evaluating the uncertainty on structural parameters derived from X-ray reflectometry measure- ments is critical for the qualification of thin film modeling, as well as for later ground calibration of Athena. Methods for uncertainty estimation across different experimental facilities are pre- sented and fit parameter sensitivities are evaluated through a novel approach using subspace analysis. Ray tracing simulation is a valuable tool to evaluate the optics performance of future X-ray missions. A general ray tracing tool is built in the McXtrace software to simulate a wide field lobster eye optics telescope. The performance is emonstrated based on design parameters for the Soft X-ray Imager on board the mission candidate THESEUS (Transient High Energy Sky and Early Universe Surveyor. A finite element analysis is implemented to the ray tracer to evaluate the effect on the optics due to thermoelastic deformations based on estimated in-orbit thermal environments.
Original languageEnglish
Place of PublicationKgs. Lyngby
PublisherTechnical University of Denmark
Number of pages131
Publication statusPublished - 2020

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