Monte Carlo Simulation And Performance Optimization Studies For HERD TRD

The astronomical research indicates that the existence of dark matter has been confirmed through the measurements such as galaxy rotation curves,gravitational lensing,and the anisotropy of the cosmic microwave background.However,its fundametal properties are still unclear.In recent years,space cosmic ray experiments have detected the anomalies in the cosmic ray positron/electron spectra in the Te V energy region from HESS,Fermi-LAT,DAMPE and CALET.However,it is difficult to prove that the anomaly is a dark matter signal,due to the systematic uncertainty of each experiment.The main scientific goal of the High Energy cosmic-Radiation Detection（HERD）facility is the high-precision hunting for dark matter signals.The Transition Radiation Detector（TRD）is used for energy cross-calibration in the Te V energy region to improve the energy measurement accuracy.Based on the energy calibration of HERD-TRD,this paper conducts a detailed study of the performance of TRD.First,the structural design of the TRD prototype is described,and the performance of the prototype is tested at DESY using the electron beam with momenta from 1.0 to 5.6 Ge V/c.Measurement results show that the Transition Radiation（TR）response of TRD exhibits a good linear increase with electron momentum in the range of 1-3Ge V/c,and tends to saturate above 4 Ge V/c.In the saturation region,the number of detectable TR-photons of the TRD prototype is 0.608_-0⁺⁰..₀₀₆⁰⁰⁸per event,with a maximum relative uncertainty of 1.56%.Secondly,in order to study the energy calibration performance of TRD in-orbit,a Monte Carlo（MC）model for the THick Gas Electron Multiplier（THGEM）TRD was established by taking advantage of GEANT4 toolkit,based on the beam test results.The MC model takes into account the transverse diffusion coefficient of electron in the drift region,the gain coefficient and energy resolution of THGEM,and the response of electronics readout.The simulation results are in good agreement with the beam test data.Finally,in order to improve the in-orbit energy calibration accuracy of TRD,the structural parameters of the TRD were optimized using the established MC model,including the parameters of the regular radiator and gas detector,as well as the thickness of the non-sensitive region.The number of detectable TR-photons of the optimized detector is 1.96 per event at above the saturation region,which is three times as many as prototype.