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.
For cosmic microwave background (CMB) telescopes, high-density polyethylene (HDPE) is widely used as reimaging lens material on account of its extremely low loss and excellent mechanical properties. The impedance mismatch between free space and lens can cause non-negligible reflection loss and low image quality. An anti-reflection (AR) coating is essential to reduce such effect. Single or multiple layers porous polytetrafluoroethylene (PTFE) membranes are glued to the HDPE lens surface as AR coatings in many previous CMB experiments. However, it is difficult to get a uniform bonding across a curvature surface for a large-aperture CMB telescope. Due to the mismatch of the thermal expansion of the lens and AR coating materials, the AR coatings have delamination or separation problem during cryogenic cycling. Simulated dielectric AR (SDAR) coatings based on the theory of meta-surface are suitable for low frequency and large aperture CMB telescopes. The effective refractive index of SDAR coating is tunable by cutting holes or grooves into the lens material to form sub-wavelength structure. The SDAR coating is made directly from lens bulk material, which can naturally solve the thermal expansion mismatch problem. In this paper, we present the SDAR coating prototype machined on a 30 mm thick HDPE plate. The measurement results show that the SDAR coating can effectively eliminate standing waves with the performance improvement about -10 dB to -20 dB. And the transmittance exceeds 98% in the 30 GHz to 50 GHz band, which is about 10% higher than that without AR coating.
The Medium Energy X-ray Telescope (ME), covering 5-30 keV, is one of the three main payloads of the Hard X-ray Modulation Telescope (HXMT). ME adopts an array of Si-PIN detectors. The detection area of one pixel is 56.25 mm2 , and the total detection area is 952 cm2 . The ME has a large active area while the pixel size is smaller. So the front-end electronics and forming electronics are realized by Application Specific Integrated Circuit (ASIC) chips. In this paper, we will describe the matching design of ME Si-PIN detector and ASIC, and the performance of the design. The energy response, temperature response, and dead time of a Two-Pixels Si-PIN detectors with the simplest readout electronics which is similar with ME, were tested on the Max Planck Institute for Extraterrestrial Physics PANTER X-ray test facility at Neuried by Munchen (Germany). The overall performance is quite similar to what was expected.
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