The Study On Temperature Dependence Of LHAASO Electromagnetic Particle Detector

It has been more than 100 years since Hess discovered cosmic rays in 1912.With the continuous development of detection technology,people have more and more profound understanding of cosmic rays.High-energy gamma rays have always been associated with relativistic particles and detection of high-energy gamma rays has become an important means to explore the origin of cosmic rays.In the past two decades,thanks to the rapid development of space and ground-based gamma-ray telescopes,such as satellites,high-altitude balloons,ground-based Cherenkov array and EAS array,more and more gamma-ray sources have been discovered.However,at the high energy end(>10Te V),the origin of cosmic rays is still not answered due to the limitation of detector sensitivity.In 2008,Chinese scientists proposed the construction of the Large High Altitude Air Shower Observation(LHAASO),a major scientific and technological infrastructure.The physical goal is to search for the origin of high-energy cosmic rays,accurately measure the cosmic ray energy spectrum in the knee region,carry out the scanning of gamma rays above very high energy in the all-sky region and detect dark matter.LHAASO,located in Daocheng,Sichuan province,is currently the world's highest and largest cosmic ray detection device,which was fully completed and put into operation in July 2021.LHAASO consists of three sub-arrays: Square-Kilometer Array(KM2A),Water Cherenkov Detector Array(WCDA)and Wide Field Cherenkov Telescope Array(WFCTA),which can realize the coincidence measurement of multiple types of detector arrays with strong observation capability.As one of the main detectors of LHAASO-KM2 A,the electromagnetic particle detector(ED)is used to accurately measure the arrival time and particle number density of EAS's secondary particles,so as to reconstruct the energy and direction information of the original cosmic ray to achieve the observation purpose.A total of5216 EDs,a large number,complex internal structure,and the requirements of the altitude of 4410 meters,ultraviolet strong humidity,the maximum daily temperature difference is up to 30? in the field environment for more than 20 years.The stability study of ED performance is of great significance for understanding its performance and improving data quality.The temperature change has different effects on sensitive luminescent materials and electronic devices in the detector,and the modulation effect of temperature is the most significant.In this paper,the contribution of each component and the characteristics of temperature coefficient in the temperature effect of the ED is studied in detail,and the attenuation variation of the detector's long time performance is obtained by correcting the temperature modulation effect,and its long time variation characteristics are given.The paper is mainly divided into the following parts:Chapter one briefly introduces the history and status of cosmic ray research,the development of detection methods and detectors,and introduces LHAASO experiment and KM2 A array.The second chapter mainly introduces the structure,the performance index and detection principle of the ED.And introduces the scintillation and wavelength shift optical fiber testing that I participated in to ensure the detector's performance.In chapter 3,the influence of temperature on the performance of on-line ED is introduced.Firstly,the temperature effect analysis method and temperature coefficient of a single detector are introduced.The average temperature coefficient of 5,038 detectors is-0.35%/?.Then the temperature effect of each component in the detector is introduced.Among them,through the experimental exploration of temperature effect of wavelength shift fiber in ED.The temperature coefficient of optical fiber is obtained through analysis about-0.094 ±0.007 %/?.The temperature coefficient is derived from optical yield and attenuation length.It is found that the temperature coefficient increases with the increase of optical fiber length.It is found that the temperature coefficient of optical fiber increases with the increase of optical fiber length.Finally,by deducting the temperature coefficient of each component,the possible explanation is given for the source of the remaining-0.2%/? temperature coefficient.In chapter 4,the application of long term stability and the temperature coefficient of EDs to charge calibration is studied.In this work,the temperature coefficient analysis method of a single detector is applied to the long-term temperature coefficient study of a full array detector.The temperature coefficient is used to correct the charge quantity of the detector,and the long-term trend of charge quantity after modification is given.In chapter 5,the sources of the remaining temperature coefficient of the detector and how to improve the quality of data analysis are prospected.