The performance of LED calibration system for Cherenkov telescope of LHAASO
2019 July 22
Each SiPM based Cherenkov telescope of LHAASO has an array of 32*32SiPMs. SiPM-based camera can be run in the moon night and achieve about 30% of duty cycle. The gain of the SiPM varies with the intensity of the sky background light. A UV-LED system is mounted at the center of the mirror to monitor and calibrate the gain of the SiPM-based camera. The LED is also used to monitor the temperature and high voltage compensation loop which is used to keep the SiPM gain stable in the case of environmental temperature changes. LED is working in the constant temperature system. The change of LED luminous intensity with ambient temperature is less than 0.8%. The first two SiPM based Cherenkov telescopes were successfully run in the first half of 2019. The design and performance of LED calibration system, which is a very important tool to monitor the gain stability of the SiPM-based camera, are presented in the paper.