Design Of High-speed Multi-channel Data Acqusition System For GEM Detector

As a new kind of position sensitive detector,GEM detector is widely used in high energy particle physics experiments and low energy X-ray imaging.Data acquisition system as an important part of the GEM detector,responsible for the detector output signal acquisition and analysis of the task,the GEM detector has an important impact on the overall performance.In this paper,regard the backend data acquisition and processing of GEM detector as the research task,and adopt FPGA logic control technology,general computer technology and information processing technology to design a multi-channel data acquisition system to implement the detector output charge signal real-time acquisition and particle imaging.Specific research as follows:(1)On the basis of understanding the functions and demand analysis of GEM detector,complete the design of system scheme.According to the working principle of the GEM detector and the readout mode of GEM detector,the charge signal is collected by selecting the Pads array readout method and the charge signal is read and converted to digital electricity by the CIPix-board chip in combination with the user's requirement of indicators,and then into the FPGA chip for digital signal processing and analysis.Finally,send the output data of FPGA into the PC for parsing and storage through the Gigabit Ethernet.(2)Completed the design of charge signal readout board.Because the effective detecting area of entrance window of the detector is 50 mm × 50 mm,the effective detecting area of the signal readout plate is 50 mm × 50 mm,the size of pixel of the each signal collecting electrode is 1.56 mm × 1.56 mm.Finally,completed the design of 32 × 32 arrays of charge signal readout board based on GEM detector.(3)Completed the design of host control circuit board.The CIPix-board is used as the front end of signal acquisition to realize 64 channels high-speed charge information acquisition,filter forming,threshold gating and multi-channel digital signal gating output,and convert the charge signal into level signal.Select the high-performance field programmable logic processor as the main controller,the design of hardware control system to achieve digital level signal read,cache,signal processing and other functions,and the signal data transmission by the Gigabit Ethernet.(4)Completed the software design of data acquisition system.In the ISE14.7 software development environment,use the Verilog HDL language to complete the design of FPGA logic program,including real-time data acquisition,data cache,data upload and downlink command parsing.Select the Windows platform,use the QT development tools to complete host computer design,implement some functions that read data from the FPGA data acquisition board,data processing and analysis,data storage,particle image display and send control instructions to FPGA data acquisition board.After completing design of the GEM detector data acquisition system,the modules are assembled and debugged.The beam velocity measurement and position imaging test are carried out by X-ray machine.The experimental results show that the DAQ system can display the two-dimensional position distribution of X-ray beam spot in real time,and the maximum event counting rate of the beam spot is more than 1M / s.With the CF-252 neutron signal source for position imaging test,and then analysis data by off-line processing method.The experimental results show that the DAQ system can clearly detect the positional information of the neutron signal scattered on the entrance window of the detector.