SiPM-Based Camera Design and Development for the Image Air Cherenkov Telescope of LHAASO

Abstract

Wide Field of View Cherenkov Telescope Array (WFCTA) has 16 image air Cherenkov telescopes and is one of the main detectors of LHAASO. The main scientific goal of WFCTA is to measure the ultra-high energy cosmic ray energy spectrum and composition from 30 TeV to a couple of EeV. Each Cherenkov telescope has an array of 32 $\times$ 32 SiPM and covers a field of view $14^{\circ }\times 16^{\circ }$ with a pixel size of $0.5^{\circ }$. Because SiPM cannot be aging under strong light exposure, SiPM-based camera can be operated in the moon night and achieve a longer duty cycle than PMT-based camera, e.g. the duty cycle of SiPM-based camera is about 30%, while the PMT-based camera is about 10%. A square SiPM with photosensitive area of 15 mm $\times$ 15 mm and Geiger-APD size of 25 $\upmu$m is used in the SiPM-based camera. Each SiPM has 360,000 APDs, which can meet the required dynamic range from 10 photoelectrons (pes) to 32000 pes of WFCTA. SiPM has higher photon detection efficiency than quantum efficiency $\times$ collection efficiency of PMT, so SiPM-based camera has the same signal to noise ratio with PMT-based camera, although SiPM has higher dark count rate.