Development of an X-ray Modulation Characterization System for HXI Payload Onboard ASO-S Mission

The Advanced Space-based Solar Observatory (ASO-S) was sent to space on 9 October 2022. As the first comprehensive satellite for solar concentrated observations of China, the ASO-S carries three payloads: the Hard X-ray Imager (HXI), the Full-disk solar vector MagnetoGraph (FMG) and the Lyman-alpha Solar Telescope (LST), respectively. The ASO-S dedicates to measuring the solar magnetic field, and observing CMEs and solar flares. As a key instrument onboard, HXI aims at imaging solar flares in hard X-rays from 30 to 200 keV with angular resolution up to 3.2", field of view of 40.3', energy resolution better than 24% at 32 keV and time cadence up to 0.125 s. Spatial modulation technique similar to YOHKOH/HXT of Japan is adopted as equipping 91 Fourier units, or tungsten grid pairs in the front and rear plates of collimator of HXI at 1190 mm distance. It is of great value to characterize modulating parameters by beam calibration before launch due to X-ray modulation relation of grid pairs are the basis of modulation imaging. For a long time, the lack of appropriate laboratory conditions has made it difficult to perform such kind of calibration test in the development of similar instrument abroad. However, we developed a practical and efficient set of X-ray Modulation Characterization System (XMCS) for the test of HXI. Firstly, the basic principle and design of HXI is introduced briefly. Secondly, ground calibration facility as well as modulation calibration requirements of HXI are presented. Detailed design and integration of XMCS were descripted subsequently. The modulation characterization test of the flight model of HXI has been successfully carried out to directly calibrate the modulation relation on the XMCS. Only part of the excellent calibration results are discussed here to verify the performance of XMCS, which shows great value and potential for the upcoming similar X-ray payloads calibration on ground.