The Wide Field Imager (WFI) is one of two focal plane instruments of the Advanced Telescope for High-Energy Astrophysics (Athena), ESA’s next large x-ray observatory, planned for launch in the early 2030s. The current baseline halo orbit is around L2, and the second Lagrangian point of the Sun-Earth system L1 is under consideration. For both potential halo orbits, the radiation environment, solar and cosmic protons, electrons, and He-ions will affect the performance of the instruments. A further critical contribution to the instrument background arises from the unfocused cosmic hard x-ray background. It is important to understand and estimate the expected instrumental background and to investigate measures, such as design modifications or analysis methods, which could improve the expected background level to achieve the challenging scientific requirement (<5 × 10 − 3 counts / cm2 / keV / s at 2 to 7 keV). Previous WFI background simulations done in Geant4 have been improved by taking into account new information about the proton flux at L2. In addition, the simulation model of the WFI instrument and its surroundings employed in Geant4 simulations has been refined to follow the technological development of the WFI camera.
KEYWORDS: Structural design, Space operations, Imaging systems, High energy astrophysics, Galaxy groups and clusters, X-ray imaging, Imaging spectroscopy, Spectroscopes, Cameras, Interfaces
The WFI instrument is designed for high-resolution X-ray imaging and spectroscopy with a large field of view. A movable mirror focuses the X-rays onto the focal plane detectors of the WFI. For design development of the instrument, structural analysis is performed from early project phases. The WFI project has entered phase B and the preliminary design is evolving towards a more detailed design including interface definitions. The focal plane of WFI consists of two detectors: Large Detector Array (LDA) and Fast Detector (FD). The LDA assembly is used for main observation modes, whereas FD is for very bright point sources. The complexity of the LDA design is due to the fact that it has to be compliant to contradictory requirements. Its sensors have to be thermally decoupled from the structure, but with a high stiffness to avoid relative displacement and deformation of sensitive components, e.g. bond wires. The LDA has an active area that is as large as ≈14x14 cm2 but the thermal gradient across it shall be below 2.5-3K. The LDA is optimized with respect to mechanical requirements for launch loads and operational conditions in space. In order to minimize mass while withstanding thermo-mechanical, static and dynamic loads, various design studies have been carried out. With the aim to develop a design, which meets all structural and functional requirements, various structural analyses are performed. In this paper, the structural design studies and the preliminary analysis results of the WFI Large Detector Array are presented.
The Wide Field Imager (WFI) is one of two focal plane instruments of the Advanced Telescope for High-Energy Astrophysics (Athena), ESA’s next large X-ray observatory, planned for launch in the early 2030’s. The current baseline halo orbit is around L2, the first Lagrangian point of the Sun-Earth system, L1 is under consideration. For both potential halo orbits the radiation environment, solar and cosmic protons, electrons and He-ions will affect the performance of the instruments. A further critical contribution to the instrument background arises from the unfocused cosmic hard X-ray background. It is important to understand and estimate the expected instrumental background and to investigate measures, like design modifications or analysis methods, which could improve the expected background level in order to achieve the challenging scientific requirement (< 5 × 10−3 cts/cm2/keV/s at 2 - 7 keV). Previous WFI background simulations1 done in Geant4 have been improved by taking into account new information about the proton flux at L2. In addition, the simulation model of the WFI instrument and its surroundings employed in GEANT4 simulations has been refined to follow the technological development of the WFI camera.
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