The high-energy cosmic radiation detection facility (HERD) is a part of the Chinese Cosmic Lighthouse Program in China space station (CSS), which is planned for launch in 2027. The HERD is expected to operate for ten years in orbit, and it will be able to indirectly detect dark matter, measure cosmic rays, and observe high-energy gamma rays. As a subdetector of the HERD, a transition radiation detector (TRD) has the main scientific goal of calibrating the electromagnetic calorimeter (CALO) at the TeV energy range, improving the measurement accuracy of the CALO, and detecting astronomical phenomena of high-energy gamma rays. In this work, we designed the front-end electronics (FEEs) as a standard readout unit for the TRD prototype in the HERD. The FEE uses four SAMPA application-specific integrated circuits (ASICs) for 128 detector signal readouts, realizing a high-speed, low-power, and high-reliability data acquisition system. The FEE receives trigger signals and serial commands from the back-end electronics (BEEs) using the universal asynchronous receiver transmitter (UART) protocol via an RS-422 bus and replies to the BEE, providing appropriate remote environmental and field-programmable gate array (FPGA) status parameters. In addition, the FEE sends detector scientific data and clock signals via a low-voltage differential signaling (LVDS) bus at 80 Mb/s with a dual-channel hot backup. According to the results of the electrical tests on the electronics, the channel's root mean square (rms) noise is less than 1.7 fC, and the linearity is better than 0.2%. In addition, a beam test is performed on the super proton synchrotron (SPS) and proton synchrotron (PS) terminals of the European Organization for Nuclear Research (CERN) to verify the electronic performance of the proposed system. The results show that the proposed FEE can meet the readout requirements of the TRD prototype and can accurately obtain the energy spectrum of muons and electrons.

This study aims to enhance the energy resolution of the Topmetal-II- pixel detector, which is pivotal for capturing soft X-ray signals and accurately measuring X-ray polarization. To achieve this, we used convolutional neural networks (CNNs) and curve-fitting techniques. The CNNs were trained on energy data from the Topmetal-II- detector to predict the peak voltage of waveforms at different amplitudes. In addition, we employed curve-fitting methods to develop a response model for the detector. We collected energy data from the Topmetal-II- using high-precision oscilloscopes, with data sampled at equidistant intervals to simulate a 40-MHz sampling rate analog-to-digital converter (ADC). Our findings indicate that a denoising autoencoder (DAE) with five encoding layers and five decoding layers, combined with a two-layer regression network, significantly improved performance. The energy deviation was reduced from 15.4 to 0.41 mY, and the energy resolution was enhanced from 24.26 to 5.09 mY, representing an approximate 4.77-fold improvement. In contrast, the curve-fitting increases the energy peak from 27.04 to 32.05 mY at an input of 350 mY, resulting in a slightly improved energy resolution. These results demonstrate substantial advancements in soft X-ray detection technology, underscoring the potential for more precise and reliable measurements in low-energy X-ray polarization detector (LPD) experiments.

The transition radiation detector (TRD) of the high-energy cosmic radiation detection (HERD) facility uses the relationship between high-energy charged particle transition radiation (TR) and the Lorentz factor to calibrate the energy of TeV-band protons in HERD calorimeters. It can also independently conduct X-ray observation and monitor gamma-ray bursts (GRBs). The TRD consists of detector units, front-end electronics (FEE), and a data acquisition (DAQ) system. The DAQ system is responsible for the overall power management of the TRD, communication, and triggering between the TRD and HERD, data processing of the detector units, control of multiple modules within the TRD, and in-orbit operation of the whole TRD. Here, we report a DAQ system of the TRD prototype, which connects six front-end circuit boards, six high-voltage (HV) circuit boards, a turntable device, an HERD trigger system, and HERD electronics. It adopts a structure with separate data and electrical components. The power sections of the FEE, HV, turntable device, and DAQ system are designed as a power circuit board, while the FEE data transmission and telemetry, triggering, main controller, storage, and communication are designed as a data circuit board. We tested the DAQ system at the European Organization for Nuclear Research (CERN), and the results show that the system can meet the requirements of the TRD prototype in terms of power, communication, data processing, and overall control. In addition, we demonstrate that the DAQ system has been redundantly designed to enhance adaptability.

The low-energy X-ray polarization detector (LPD) is a large-area and wide-field-of-view (FoV) X-ray polarimeter planned to be installed on the China Space Station. The LPD is designed to measure the polarization of gamma bursts and their early X-ray afterglows, facilitating studies of celestial bodies and radiation mechanisms at the centers of gamma bursts. The LPD consists of 15 detection units with identical structure and function. A detection unit prototype was developed, featuring six pixel detectors compactly placed on a bonding and front-end electronics (BFE) board with an effective detection area of 27.36 cm(2). Each pixel detector has 16 analog output channels, after which data are amplified, digitized, and transmitted via the board-to-board (BTB) connector to the data acquisition (DAQ) board for processing. The prototype also includes an internal high-voltage circuit with up to -4-kV voltages. The test results indicate that the detection unit prototype can simultaneously read data from 96 channels of pixel detectors with an equivalent charge noise of 49.49 e(-). It features comprehensive power management, offers configurable data compression, storage, and encoding, and meets all functional requirements of the detection unit.

POLAR-2 is a gamma-ray burst (GRB) polarimeter that is designed to study the polarization in GRB radiation emissions, aiming to improve our knowledge of related mechanisms. POLAR-2 is expected to utilize an on-board polarimeter that is sensitive to soft X-rays (2–10 keV), called low-energy polarization detector. We have developed a new soft X-ray polarization detector prototype based on gas microchannel plates (GMCPs) and pixel chips (Topmetal). The GMCPs have bulk resistance, which prevents charging-up effects and ensures gain stability during operation. The detector is composed of low outgassing materials and is gas-sealed using a laser welding technique, ensuring long-term stability. A modulation factor of 41.28

The Topmetal detector, utilized in this investigation, is a direct-type CMOS pixel sensor known for its distinctive feature of employing exposed metal at the top of each pixel to directly capture external charged particles. This method generates electrical signals through the induction of charge. At present, it is mainly used in gas pixel detector(GPD) and particle beam monitoring. In this paper, we present a new front-end design aimed at enhancing the capabilities of the Topmetal pixel detector. The focus is on incorporating a Time-Digital Conversion (TDC) ASIC into the front-end, with the objective of achieving high-precision time measurement in addition to superior position resolution. The function of the TDC is achieved by the two reverse delay chains, 11 edge acquisition circuits Time-to-Amplitude Converter (TAC), analog gate, weight count module, and Wilkinson Analog-to-Digital Converter (ADC). Coarse time measurement is implemented based on a counter with a working frequency of 500 MHz, and fine time measurement is implemented by the combination of TAC and ADC. The design prototype was taped out with the GSMCR130 nm technology. Test results show that this circuit can handle up to 11 consecutive cases, with the minimum time interval of adjacent cases being 500 ps and the bin size up to 2 ps. The time measurement precision is better than 50.3 ps RMS and the PVT(Process Voltage Temperature) robustness of the input delay chain circuit is validated, showing the stable performance of the design.

The Gas Microchannel plate Pixel Detector (GMPD) is purposefully designed and manufactured for astrophysical X-ray polarization detection, slated for use in various space missions such as the Cosmic X-ray Polarization Detector (CXPD) CubeSat, Low Energy Polarimeter Detector (LPD/POLAR-2), and the Chasing All Transients Constellation Hunters (CATCH). Past research has explored the polarization and spectral performance of GMPD. This study, for the first time, experimentally investigates its imaging characteristics to validate its imaging capabilities. Utilizing a deconvolution method, we measured the position resolution of GMPD, revealing distinctions in the detector's imaging capabilities for X-rays of varying energies and in orthogonal directions. These research findings will provide targeted insights for optimizing the photoelectron track reconstruction algorithm and correcting systematic effects in polarization measurements for future applications of GMPD.

This study presents an electronics system for cosmic X-ray polarization detection (CXPD). The CXPD was designed as a high-sensitivity soft X-ray polarimeter with a measurement energy range of 2–10 keV carried by a CubeSat. A stable and functionally complete electronics system under power and space constraints is a key challenge. The complete CXPD electronics system (CXPDES) comprises hardware and firmware. CXPDES adopts a three-layer electronic board structure based on functionality and available space. Two gas pixel detectors (GPDs) were placed on the top layer board, and CXPDES provided the GPDs with voltages up to - 4000 V. Each GPD signal was digitized, compressed, encoded, and stored before being transmitted to the ground. The CXPDES provided stable and high-speed communication based on a scheme that separated command and data transmission, and it supports the CXPDES in-orbit upgrade. In addition, environmental monitors, silicon photomultiplier (SiPM) triggers, power management, GPDs configuration, and mode switches were included in the overall operating logic of the CXPDES. The results obtained by testing the CXPDES showed that it satisfied all the requirements of CXPD. The CXPDES provides design experience and technological readiness for future large-area X-ray polarimetry missions.

This article presents the design and implementation of a soft X-ray polarized calibration platform based on Bragg’s Law and Fresnel’s Law, which is used to calibrate low-energy polarization detector(LPD/POLAR-2) that has potential deployment onboard the China Space Station. The platform is equipped with versatile equipment that can generate both completely and partially polarized X-ray beams, and provides precise control over the diffraction angle, achieving the desired polarization degree. It covers the 3–8 keV energy band, with a high fraction of monochromatic light (>93

The low-energy polarization detector (LPD), a payload of the POLAR-2 mission, is a soft X-ray polarization detector with a wide field of view and a large array aimed at measuring X-ray transients. These transients exhibit rapid intensity changes of several orders of magnitude, making it crucial for polarization detectors to have front-end electronics with low dead time, fast readout capabilities, high time resolution, and good energy resolution. In this article, we present the design of the front-end electronics, which consist of a rolling shutter CMOS pixel charge sensor (Topmetal- $II^{-}$ ) and a gas microchannel plate (GMCP) bottom amplifier circuit. Topmetal- $II^{-}$ 's rolling shutter readout provides fast scanning of large pixel arrays without dead time and acquires 2-D images of photoelectron tracks. Meanwhile, the GMCP's bottom amplifier circuit measures the energy and time of the X-ray. The front-end electronics are employed by the CubeSat cosmic X-ray polarization detector (CXPD), a proto-flight model of the LPD, achieving a timing resolution of 19 ns, and an energy resolution of 16.5% for linearly polarized X-rays at 8 keV.

X射线偏振探测立方星载荷(China Space X-Ray Polarization Detection System,CXPD)致力于检测空间X射线偏振度、能谱等信息,用于理解天体物理现象.为满足安全性强、功耗低、成本低的小型卫星载荷存储需求,本工作选择具有错误检查和纠正、掉电保存、坏块管理等功能的内嵌式多媒体存储卡作为存储介质.针对卫星载荷在太空特殊环境下的上电操作和星载设备的数据吞吐量需求,结合eMMC5.0协议,研究了基于现场可编程门阵列(FPGA)控制的星上存储系统.该系统在高低温试验测试、振动测试和长时间alpha源照射测试中均能稳定运行.