The Readout Electronics Research Of MWPC Based The Center Of Gravity Method

China Spallation Neutron Source is the advanced neutron source based advanced accelerator technology,it mainly consists of a negative hydrogen linear accelerator of 80MeV,a fast circulation proton synchronization accelerator of 1.6GeV,a target station,three neutron spectrometers and the corresponding matched facilities.Three spectrometers contain multi-function reflected spectrometer,small angle scattered spectrometer and high throughput powder diffracted spectrometer.As the first spallation neutron source of developing country,it will constitutes the four largest pulsed spallation neutron source of the world with the running neutron source in USA,Japan and UK when it is completed,it will greatly enhance the basic research and high technology of China and shortening the gap of thirty years between our country and the frontier of the world.The paper researched the two dimensional position of particles and design and implementation of readout electronics system according to the MWPC used in the multi function reflected spectrometer.When the neutron entering the MWPC that is full of 3He,it will react with them and generation the secondary particles such as electrons and positive ions,the positive ions cloud avalanched from electrons near the anode wire and drift to cathode,so the induced charge will be generated on the two cathode surface,the value of the charge of each channel is related to the position of electronics that original ionization produced,it only needs to measure the value of the charge in each channel,and then using the center of gravity method could estimate the two dimensional position of the electrons that avalanched.This design contains a total of 150 channels,while fifty channels in the direction of X and one hundred channels of Y.The system in the circuit board uses FPGA as the core of data processing,and contains analog signal input module,analog digital conversion module and network output module.The analog signal input stage uses charge sensitive preamplifier,and integral the weak current signal from detector,after filtering molding processing then to be quasi Gauss wave,and control the right magnification,at this moment the output is a voltage signal that proportional to the amount of charge,and content to the input requirements of ADC.In ADC,signal converted to digital through sampling the analog signal,searching the peak and it is the charge.In order to improve the data processing ability,the design uses two FPGA,using the structure of daughter-mother board,FPGA on the daughter board uses to search the peak and the other on mother board uses to number the data and packing,through the TCPIP network protocol and the data is sent to the PC for next step.The signal is very weak from the detector,for the convenience of signal processing,the signal must be amplified.The design uses a charge sensitive preamplifier can preliminary amplify and integration the signal effectively,using eight channels input ADC,not only satisfied the design requirements,but also reduced the design cost,and the design of two FPGA could reduce hardware load in order to improve the reliability of the design.Comparing to the traditional readout electronics system of MWPC which need judge whether over the threshold only,this design requires to accurate readout the charge value,it's more complex but a higher accuracy.The design has a very important theoretical and practical significance and laid a good foundation for the future's engineering practice.