Research On Counting Rate Test System Of LHAASO-KM2A And Performance Of Power Supply

The Large High Altitude Air Shower Observatory(LHAASO),located in Haizi Mountain,Daocheng City,Sichuan Province,is one of the major scientific and technological projects during the 12 th Five-Year Plan period of China.Its core scientific goal is to explore the origin of high-energy cosmic rays.The 1 square kilometer detector array(KM2A)contains 5195 electromagnetic particle detectors,and the power supplies maintain good performance in high altitude environments is the basic guarantee for the normal operation of the detectors.For this reason,a program-controlled power supply specially designed for detectors has been produced,which has the advantages of small size and low noise and can meet the requirements of the experiment.In the early stage of the project,many power supplies with good test results of conventional parameters were sent to the Daocheng experimental site,but the actual operation of the power supply was not ideal.Therefore,the performance index of ED was studied--counting rate,which can reflect noise level and performance stability of detector.The author's team developed the counting rate test system and examined power supplies.The power supply which can guarantee the test result is qualified runs well in the observation station.At present,5,381 power supplies with good test results have been running normally in the observation station.The ED can work normally,which provides the important guarantee for the smooth implementation of project.It has important scientific significance.The counting rate test system consists of photomultiplier tubes,readout electronics,White Rabbit switches and data acquisition system.In order to make the system stable operation under low threshold,a large number of experiments have implemented to find the influencing factors of counting rate,such as the distance between the components,then constantly upgrading,12 channel parallel test system have been developed.It can test twelve power supplies at the same time.The system can run stably for a long time.The development and experimental exploration of counting rate testing system is one of the innovation points of this thesis,it has good practical value and practical significance.For observatory station,electromagnetic particle detector counting rate rise at low temperature,the power supply noise characteristics and the low temperature readout electronics threshold effect are studied.It found that low temperature will send up the power supply noise amplitude increases and spatial noise radiation enhancement,resulting in higher detector counting rate.In order to solve the influence of high power supply noise on the counting rate of detector in low temperature environment,according to the experimental fitting formula in this thesis,the threshold required to eliminate the noise of the power supply can be calculated to make the counting rate stable.However,the threshold adjustment amplitude of this scheme is too large,which will increase the detector threshold energy and lead to the reduction of the signal-to-noise ratio.Therefore,the solution proposed in this thesis is to take insulation measures for the power supply to curb the increase of space noise radiation and improve the performance and stability of the detector.The solution is verified by test,and it is proved to be feasible.This is one of the emphases and innovations of this thesis.According to the solution proposed in this thesis,it can reduce the interference of power supply noise to the ED counting rate and solve the problem of the ED counting rate instability at low temperature.It has certain practical value and scientific significance.In addition,the effective threshold of readout electronics can be compensated according to the experimental method in this thesis,so that the detector can work at the optimal signal-to-noise ratio.In the end,the main content and innovation of the thesis are summarized.The research work is discussed,and the future work is prospected.