Research On Readout Methods And Prototype System For VLAST Calorimeter

The search for and study of dark matter has become a frontier of physics,and the observation of cosmic rays and gamma rays provides an effective means of indirectly detecting dark matter particles.Gamma rays,in particular,offer a unique window into observing extreme astrophysical phenomena in the universe and serve as an important probe for studying the origin of cosmic rays,the composition of the universe,and the evolution of stars.The DArk Matter Particle Explorer(DAMPE)was successfully launched in 2015 and has made significant progress in direct detecting cosmic rays and gamma rays.However,the size of the DAMPE detector limits its acceptance for gamma rays.Therefore,the Very Large Area gamma-ray Space Telescope(VLAST)has been proposed by scientists from the DAMPE collaboration to develop a world-leading space-based detector for gamma rays.The VLAST is designed to observe gamma rays in the energy range of MeV～TeV with unprecedented acceptance,and is expected to achieve breakthroughs in dark matter,astrophysics,and cosmic ray detection.For the preliminary design,the VLAST consists of three sub-detectors:the Anti Coincidence Detector(ACD),the Silicon Tracker and low Energy gamma-ray Detector(STED),and the High Energy Imaging Calorimeter(HEIC).Among them,the HEIC not only measures the deposited energy of the incident particle,but also distinguishes particle based on the shower image in the calorimeter.The preliminary scheme of the VLAST calorimeter is a homogeneous calorimeter using long bismuth germanate(BGO)scintillation crystals as absorbers and detectors.The entire calorimeter is expected to measure high-energy electrons and gamma rays ranging from 0.1 GeV to 20 TeV.Through simulation,the energy deposited on a single crystal detector unit is approximately in the range of 0.1 to 2 × 105 MIPs.This necessitates the need for photodetector readout devices and readout electronics to reach a dynamic range of six orders of magnitude.The main focus of this thesis is to achieve a calorimeter readout scheme with high energy resolution and a large dynamic range by using a combination of Silicon PhotoMultiplier(SiPM)and multi-PhotoDiode(PD),and to design the corresponding readout electronics and detector prototype system.First,the calorimeter readout systems of some similar high energy detectors around the world are investigated.The readout methods and system architectures adopted in each experiment are summarized in this thesis.According to the design and demand of the VLAST calorimeter,a large dynamic range readout scheme based on semiconductor photodetector is proposed,which can achieve a wide dynamic range by splicing the ranges of multiple readout devices.As part of the research for the VLAST calorimeter,two front-end electronic circuits are realized,one using OPerational Amplifiers(OPAs)and the other using Application-Specific Integrated Circuits(ASICs).The dual-gain readout circuit,based on the OPAs and some discrete components,is mainly composed of charge sensitive amplifiers,filter amplifiers,peak detectors,and other modules.This circuit is mainly used for the research and testing of photoelectric readout devices,because its parameters can be adjusted flexibly.The ASICs based front-end electronics are characterized by high integration and scalability,and are mainly used in ground-based calorimeter prototype readout systems.In addition to the front-end electronics,the development of the corresponding trigger system and data acquisition system,including both hardware and software components,has also been undertaken.Consequently,a small calorimeter prototype system has been successfully assembled.Moreover,a series of tests has been conducted on the prototype system to validate its functionality and performance.The electronics tests mainly evaluates the readout function,linearity,noise,and other properties of the electronic system.The readout device test is performed to calibrate the gain of the photodetectors,using a Light Emitting Diode(LED)to generate light pulses.And the prototype system test is mainly based on ground-based cosmic rays experiments.The preliminary test results demonstrate that both front-end electronics of the two approaches are capable of achieving a large dynamic range readout.Within the linear dynamic range,the nonlinearity of the readout electronic channels is superior to 1%.When combined with the crystal detector unit,the measurement dynamic range of the readout system for both two schemes is essentially comparable.The noise level is below 0.1 MIPs,the highest energy that can be measured exceeds 1.6 × 105 MIPs,and the dynamic range is more than 106.In this work,a large dynamic range readout scheme is designed for the VLAST calorimeter,and the prototype of the detector is developed.The feasibility of the readout scheme is preliminarily demonstrated,which provides a technical reference for further research on the high energy imaging calorimeter.