Research On The Data Filtering Method Of GEM Neutron Monitor

The intensity of the neutron beam produced by a spallation neutron source has irregular characteristics over time,and the flux and energy of the neutron beam need to be monitored before it is injected into the sample.The GEM gas detector has the advantages of high count rate and good spatial position resolution,which is applied by CSNS to monitor the neutron beam.The GEM neutron monitor uses the neutron time of flight method to calculate time of flight and plot the corresponding spectra,which requires the proton hitting cycle T0 signal as the starting time of flight.But in fact the GEM neutron monitor electronics system must be operationally logically related only to the hitting moment of the neutron instance,not to be tied to the T0 signal.To uncouple the tight relationship of the GEM neutron monitor electronics system with the T0 signal,a method is proposed to filter the neutron data of the GEM neutron monitor using the T0 signal time data of the proton beam intensity monitor.In thesis,the following work is studied for the GEM neutron monitor data filtering method:(1)The WR clock synchronization technology used in the CSNS high-precision timing system is studied,including the technology principle of PTP,Sync E,and DDMTD.Based on the simplified WR clock synchronization link model,the calibration methods of hardware delays,fiber propagation delays and bitslide value are studied to ensure the accuracy of time stamps of marker signals of monitors and other devices.(2)The offline filtering method of GEM neutron monitor data is studied.An offline filtering algorithm based on group searching algorithm is proposed to achieve the purpose of filtering neutron data from GEM neutron monitor using the T0 signal time data of the proton beam intensity monitor,as well as calculating neutron time of flight,counting neutron flux and plotting time of flight spectra based on the filtered reorganized data package.(3)The real-time filtering method of GEM neutron monitor data is studied.Based on the dichotomous searching algorithm and multi-threading techniques,the functions of receiving,analysing and filtering time data in real-time during the experiment and uploading the calculated neutron time of flight to My SQL database are realized,and finally the Grafana platform is used to interface with the database to realize the real-time monitoring of neutron data.(4)The content of the relevant method validation is studied.Using the WR clock synchronization system built in the laboratory,the correctness of the time delay parameters calibration method and the performance of the WR clock synchronization network were tested,which can make the clock synchronization accuracy stable at the sub-nanosecond level and meet the timing performance required by CSNS;the feasibility of the GEM neutron monitor data filtering method was verified,and the tight relationship of the GEM neutron monitor electronics system and the T0 signal was uncoupled to achieve monitoring of neutron flux and time-of-flight distribution;the program performance of the real-time filtering method for GEM neutron monitor data was tested and satisfied the engineering requirements.