The Large Area Detector (LAD) is the high-throughput, spectral-timing instrument designed for the eXTP (enhanced Xray Timing and Polarimetry) mission, a major project of the Chinese Academy of Sciences and China National Space Administration. The eXTP science case involves the study of matter under extreme conditions of gravity, density and magnetism. The eXTP mission is currently performing a phase B study, expected to be completed by the end of 2024. The target launch date is end-2029. Until recently, the eXTP scientific payload included four instruments (Spectroscopy Focusing Array, Polarimetry Focusing Array, Large Area Detector and Wide Field Monitor) offering unprecedented simultaneous wide-band X-ray timing and polarimetry sensitivity. The mission designed was however rescoped in early 2024 to meet the programmatic requirements of a final mission adoption in the context of the Chinese Academy of Sciences. Negotiations are still ongoing at agency level to assess the feasibility of a European participation to the payload implementation, by providing the LAD and WFM instruments, through a European Consortium composed of institutes from Italy, Spain, Austria, Czech Republic, Denmark, France, Germany, Netherlands, Poland, Switzerland and Turkey. At the time of writing, the LAD instrument is thus a scientific payload proposed for inclusion on eXTP. The LAD instrument for eXTP is based on the design originally proposed for the LOFT mission within the ESA-M3 context. The eXTP/LAD envisages a deployed >3 m2 effective area in the 2-30 keV energy range, achieved through the technology of the large-area Silicon Drift Detectors - offering a spectral resolution of up to 200 eV FWHM at 6 keV - and of capillary plate collimators - limiting the field of view to about 1 degree. In this paper we provide an overview of the LAD instrument design and the status of its maturity when approaching nearly the end of its phase B study.
This paper reports a highly reliable piezoelectric Micro Electro Mechanical System (MEMS) Fast Steering Mirror (FSM) with large optical aperture (10 mm), which utilizes two-level-construction comprising a mirror plate and a actuator hidden beneath the mirror plate, achieving a high resonant frequency (⪆900 Hz) and a large quasi-static scanning range (4 mrad). The leverage structure is adopted not only to amplify the quasi-static deflection angle, but also to achieve a high fill factor (⪆50%). Moreover, compliant flexural structures are optimized to balance the stress to strengthen mechanical robustness. AlScN piezoelectric film is used as actuating material for high piezoelectric coefficient, high linearity and long-term stability. Through experimental verifications, the mirror has been proven to have high mechanical and thermal robustness, namely, withstands mechanical vibration (14.34 g), shock (500g@2ms) and temperature cycling (-40° to 80°) without performance degradation. Meanwhile, the on/off at equal stress experiment further demonstrates the lifetime of the mirror to be more than 12.0E9 cycles.
To achieve accurate detection of different space x-ray sources, three types of filters are designed for the follow-up x-ray telescope onboard the Einstein probe (EP). Two of them are supported by PI mesh and Ni stiffener, which are studied in this paper. Since visible light blocking performance of these filters is important for x-ray detection, the transmittance and visible light irradiation damage performance of them are measured and presented. With a self-built double-beam laser system, the detection sensitivity of transmittance at 532 nm is increased to 10 − 9 compared with 10 − 5 for the spectrophotometer. Moreover, the tests of visible light irradiation damage performance under vacuum and air conditions have been carried out using this system, which proves that the filters have good reliability. Finally, the topography of these filters is studied and described with a microscope.
The enhanced x-ray timing and polarimetry mission (eXTP) is a flagship observatory for x-ray timing, spectroscopy and polarimetry developed by an international consortium. Thanks to its very large collecting area, good spectral resolution and unprecedented polarimetry capabilities, eXTP will explore the properties of matter and the propagation of light in the most extreme conditions found in the universe. eXTP will, in addition, be a powerful x-ray observatory. The mission will continuously monitor the x-ray sky, and will enable multi-wavelength and multi-messenger studies. The mission is currently in phase B, which will be completed in the middle of 2022.
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