The Performance Analysis Of Low Energy Telescope Detector

In modern space astronomy research, X-ray astronomy research holds an important position. In order to develop our national X-ray astronomy research, Chinese scholars indigenous designed an advanced space X-ray observation device—Hard X-ray Modulation Telescope (HXMT).HXMT mission was put forward in 1993. Since 2000, the Pre-researching work of HXMT was supported by the Major State Basic Research Development Program of China (973 Program), the Knowledge Innovation Project's Major Directional Program of Chinese Academy of Sciences and the 985 Program of Tsinghua University. The Pre-researching work of HXMT has completed the development of Payload's test setup. At present, the HXMT mission is in the later period of Pre-researching work. One of the major scientific objective of HXMT mission is carrying out the high sensitivity and high resolution Hard X-ray sky survey, discovering large quantities of super massive black holes and unknown types of celestial bodies which are masked by space dust, analyzing and confirming the sources of space Hard X-ray background radiation; The other major objective is analyzing the dynamics and high energy radiation process of compact objects and black hole gravity field, carrying out high accurate fixed-point observation to high energy celestial bodies such as black holes, neutron stars, active galactic nucleus and so on, analyzing the Light Variability, spectrum and high energy particles'accelerating mechanism of high energy celestial bodies.HXMT will complete the X-ray sky survey among 1~250keV, in which the X-ray among 1~15keV will be surveyed by a subsystem—Low Energy Telescope (LE).According to the functional task of LE, LE chooses a new-style semiconductor detector—Swept Charge Device—as the soft X-ray detector.On the basis of Swept Charge Device's working principles, this paper deeply researched the detector's performance.This paper researched the damage mechanism of LE detector caused by space radiation effects, believed that ionization effect and displacement effect are the major damage effects to Swept Charge Devices. In addition, the electronic system of the detector would also be damaged by space radiation effects. This paper gave the following radiation protection measures for LE.In order to relieve the radiation damage, almost all of the space missions adopted protective layer to shield the space radiation. Aerospace equipments usually select aluminum or tantalum as the protecting materials. For the materials which have the same thickness, the atomic number is bigger and the shielding effectiveness is always better, but the atomic number is bigger, the secondary radiation induced by material is more. In the situation of limiting the thickness and ignoring the weight, tantalum is the most ideal protecting material; If the space mission needs to consider the weights of the load and the secondary radiation induced by material, aluminum is the most ideal protecting material. This paper suggested that choose aluminum as the protecting material for LE.The damages to detector's integrated circuit and external electronic system caused by space radiation should not be neglected, this paper suggested that the external electronic system should choose high grade integrated circuit and components, and quantitative evaluation of electronic system's radiation resistance should be carried out.This paper suggested that when HXMT run across the South Atlantic Anomaly, it should adjust the Satellite Attitude to make the axial direction of LE's collimator perpendicular to the radiating direction of high energy particles, because the Swept Charge Device's sensitive chip is very thin, this way will reduce the accepted radiation dose.This paper's main content is the performance analysis of detector in chapter 4. The performance test was accomplished on the testing system which had been developed by LE research group. The performance test includes temperature's influence, operating voltage's influence and the energy linearity of the detector.The test discovered that temperature has large influence on the performance of the detector and conforms to the theoretical prediction. The detector already has good energy resolution (175eV@5.9keV) and very low total noises (about 12 electrons) when at -10 centigrade, which has fulfilled the LE's energy resolution demand (450eV@5.9keV). The operating voltages also have large influence on the performance of the detector, the driving clock's voltage (IΦ) influences the performance (energy resolution, total noises, fraction of split events, signal amplitude) in a certain degree; the substrate voltage (Vss) influences the performance of the detector associated with IΦ; the output source follower voltage (Vod) just influences the signal amplitude in a certain degree associated with Vss; the voltage of charge collection (Vog) just influences the signal amplitude in a certain degree. This paper gave the reasonable explanation to why some performance parameters were influenced by temperature and operating voltages, but the mechanism of some individual performance parameters influenced by temperature and operating voltages remains unclear, we hope for the further researching.By the experiment analysis, we found that the detector's energy linearity is very good, which could satisfy LE's need for detecting the energy spectrum of soft X-ray.In addition, this paper analyzed the parameters'influencing degree to the performances of the detector, and determined the best working conditions for the detector.Finally, depending on the conclusions of the performance analysis, this paper gave several opinions to the Swept Charge Device's readout circuit designing, including optimizing the signal amplification circuit and simplifying the circuit, reducing the power consumption (avoid the noise introduced by high power consumption); further studying should be carried out for signal amplitude's variation (expect to make the signal amplitude stable by circuit designing); further studying should be carried out for the fraction of split events'changing; further optimizing the temperature monitoring circuit to acquire more accurate, more stable temperature data from the detector.