Design and on-site test of the portable calibration system of WFCTA for LHAASO

Purpose The wide field of view Cherenkov telescope array (WFCTA) consists of 18 Cherenkov telescopes used for measuring and analyzing cosmic ray energy spectra. In order to calibrate WFCTA in measuring energy, the horizontal attenuation length and phase function of atmospheric aerosols need to be precisely measured. A portable calibration system was designed to study aerosols in the field of view of WFCTA by emitting laser at a sufficient distance.
Methods A portable calibration system, a component of WFCTA, is designed to surround by an aluminum frame. As the core of the system, an Nd:YAG laser and a rotating part to control the laser shot pointing to the field of view of WFCTA, are built up as well as multiple subsystems. In addition, it also has damping components that provide protection for equipment and light paths during transportation and operation. It was assembled and debugged in the laboratory of Southwest Jiaotong University.
Results and conclusion During the on-site testing, the laser beams emitted by the system passing through the field of view of the telescope according to the predetermined trajectory, present clear images with an maximum deviation of 0.94° on elevation and 0.11° on azimuth and with the pointing stability less than 0.1°, which verify the reliability of the system.