Research On Digital Pulse Algorithm Of CsI(Tl) Detector Array At External Target Facility Of HIRFL-CSR

A full digital approach of data acquisition system was chosen to fulfill the upgrade work of CsI(Tl)array at External Target Facility(ETF)of Heavy Ion Research Facility in Lanzhou.The CsI(Tl)detector array consists of 1024 CsI(Tl)crystal detectors with high number of channels and high density of detection units,and the electronics and data acquisition system need to be highly integrated.Thus,the digital algorithms in Field Programmable Gate Array(FPGA)should be handled,and finally only physical quantities such as signal energy,time and particle identification parameters are output to achieve data compression.In order to select a suitable online digital pulse processing scheme for CsI(Tl)detector array and apply it to the beams experiment of ETF.In this paper,a test platform including CsI(Tl)crystal array unit and DAQ system is constructed,which is divided into waveform mode and algorithm mode.The original waveform is obtained by usingγandαradioactive sources and the algorithm is tested and verified.Secondly,various digital pulse processing algorithms are used for off-line analysis of waveform data,including the moving average filters(MAF)in filtering algorithms,averaging,median and iterative methods in baseline restoration algorithms,leading-edge discrimination(LED)and constant-fraction discrimination(CFD)in temporal information extraction algorithms,cusp filter,CR-RC~m filter and trapezoidal filter in energy information extraction algorithms,charge comparison method,rise time method and RPID algorithm in particle identification.After comparing and analyzing the energy resolution of different energy information extraction algorithms and the Figure-of-Merit of particle identification,a digital pulse processing algorithm for CsI(Tl)detector array is finally determined,which is aimed at detecting gamma rays and charged particles.Finally,the scheme,which includes 8-points moving average filter,average method in baseline restoration,leading-edge discrimination,moving window deconvolution,and digital charges comparison,is formed and implement into FPGA.The online algorithm was tested and verified by the test platform.The energy resolution of online MWD forming energy extraction was 5.243%@1.33Me V.The particle identification effect of digital constant fraction charge comparison method Fo M=4.995.All the algorithms have achieved good performance and the results are consistent with the off-line analysis,which indicates that this scheme of digital algorithms meets the demands.