The Optimization Study Of HERD's Transition Radiation Detector

The High Energy cosmic Radiation Detection Facility(HERD)is one of the scientific payloads planned for the Chinese space station in the future.Its scientific objectives are to detect dark matter with unprecedented sensitivity,accurately measure the energy spectrum and composition of cosmic rays in the Milky Way,and carry out related observations on high-energy gamma ray surveys.Aiming at the above scientific goals,HERD puts forward a number of innovative designs,one of which is to calibrate calorimeter in the TeV energy range by means of transition radiation detector(TRD).The TRD is the payload of the HERD.It can achieve HERD's ability for searching dark matter with wide-energy range and high-precision by calibrating calorimeter.The significant TR signal is the prerequisite in calibrating the calorimeter precisely with TRD.In order to improve the Signal-to-Noise Ratio(SNR)of TR as much as possible,the parameters affecting TR-spectrum in the radiator,such as the type of material,the foil and gap thickness and the layer number,were studied in depth.The detection gas,sensitive thickness,THick Gas Electron Multiplier(THGEM)and electronic readout system in the detector were designed in detail.Then a new prototype of TRD called Side-On TRD was proposed to distinguish TR signals significantly from ionization energy loss background.Considering the simulation and optimization results,experimental test results,HERD's design requirements and cost,the optimal parameters of radiator are as follows:20-?m polypropylene foils,500-?m air gaps,with the number of layers being 300.The detection gas are 90%Ne+10%CO₂,with sensitive thickness being 5 cm and divided into 64 parts.The layer of THGEM is 2.The side-on TRD prototype has been tested at CERN,further we process the data from five electronic channels of TR signal completely deposited,and found that the experimental results are consistent with the GEANT4 simulation with a significant TR signal,and the signal significance of TR is 6.16?.This verification result shows that the TRD's simulation and optimization work carried out in this study is correct and reliable,and also lays the foundation for the later engineering design of TRD and in-orbit energy calibration of the calorimeter in HERD project.