The Research On The Readout Electronics For The Calorimeter Detector Of The Dark Matter Exploration Satellite

In recent years, more and more?astronomical observation results show that only a tiny part of the universe is made of baryonic matter which can be explained by the Standard Model, while others are dark matter and dark energy which we have few knowledge about, except their gravitational effects. The study and detection of dark matter will probably lead to new revolution of existing physics theory.Searching the high energy baryonic particles, such as high energy gamma rays, electrons, positrons, anti-proton, etc, which may be produced by annihilation of dark matter particles, is an important method of dark matter detection and a hot topic in the international scientific community. Many countries have carried their space-based dark matter detection experiments, such as the ATIC Antarctica Balloon experiment and the Fermi satellite proposed by the United Sates, the PAMELA satellite of Italy. There are also experiments in progress, such as AMS02 experiment proposed by American, and the CALET detector supported by Japanese government.In China, a scientific satellite devoted to the study of dark matter particles has been proposed mainly by the Purple Mountain Observatory of CAS, and its physics goal is to find the existence evidence of dark matter particles by investigate the composition and energy spectra of primary cosmic rays, especially for electrons, positrons and gamma rays, over the dynamic range from 5 GeV to 10 TeV. The major part of the satellite payload, which is a critical sub-detector for measuring the energy of cosmic particles, will be a calorimeter composed of a stack of BGO (Bismuth Germanate) crystals. To achieve the energy dynamic range up to 10 TeV, the read out electronics system of the calorimeter should have 1728 PMT channels, with a dynamic range of nearly one thousand in each channel. Also some other strict requirements for the readout system are needed, due to the special environment of spacecraft, such as ultra-high reliability, ultra-low power consumption, etc. This dissertation mainly discusses the readout electronics system of this calorimeter, including the technology of charge measurement, the interconnection of electronics modules. Then the implementation details of a prototype readout system used for the ground-based small-system cosmic ray test are introduced, and finally a preliminary consideration of the reliability of the future electronics system in space application is also concerned. In the first two chapters, the project background is introduced, including the basic knowledge of dark matter, the plan of the dark matter detection satellite, and the design concept of the calorimeter detector.The calorimeter will consist of 576 BGO crystals, each with a R5611 PMT for signal output. According to the design goals, each crystal, together with its PMT and electronics channels, have to cover a deposited energy range from 11.5 MeV (0.5 MIP) to 1.7 TeV. Thus the PMT bleeder string base incorporates a three dynode pickoff to enlarge the dynamic range of charge measurement. In Chapter 3, the details of charge measurement circuit will be discussed, such as the pre-amplifier, the analog-process methods and the digitization of analog signals. Finally three basic types of charge measurement method are introduced: the charge-to-voltage conversion method, the charge-to-time conversion method and the waveform sampling method. ASIC chips based on the traditional charge-to-voltage conversion method, is considered as the most suitable choice for this electronics system, because of its low power dissipation, high integrity level, and high reliability features.Chapter 4 is mainly about the VA32HDR14.2 ASIC adopted in the current design, and about the charge measurement scheme based on this chip. In order to check the feasibility of this scheme, a conception electronics module was designed, and the test results using signal generator and detector signals are introduced as well.From Chapter 5 to Chapter 7, a prototype readout system for the ground-based cosmic ray experiment is discussed. Based on the work introduced in the former chapter, we successfully designed 6 Front End Electronics (FEE) modules, 2 Data-Acquisition (Sub-DAQ) modules and a DAQ software running on PC, to form a readout system for the prototype detector. The FEE Module is assigned to the charge measurement of 96 PMT signals, using 3 ASIC chip, and can satisfy the requirements of high integrity and low-power. The Sub-DAQ module is used to to generate trigger signals, to readout event data from FEEs, and to send the data to PC. In these three chapters, the implementation of hardware modules, the interconnection buses, and the DAQ software are detailedly introduced.Chapter 8 discusses the error analysis and test results of the prototype readout system. The process of tests includes two steps: the electronics stand-alone tests, and joint tests of the detector-electronics system. For the former step, we use a signal generator and the calibration circuit on FEE modules as signal sources, to test the readout ability, the linearity, the statistic error, the stability and the crosstalk of the readout system. The latter step includes tests using the crystal-test platform, and the formal prototype detector for ground-based cosmic ray experiment. Test results show that the performance of the prototype readout electronics can basically meet the requirements of the ground-based prototype detector.Considering that reliability is the most crucial specification of the satellite payload, the basic issues on the reliability of aerospace electronics are discussed in Chapter 9. And a draft plan of electronics radiation tests is proposed, for the future prototype phase and the flight model phase of this project.