Flat-fielding of the Photomultiplier Camera of the Phase I HESS Cherenkov Telescopes

Abstract

This paper describes the calibration system which has been designed for the flat-fielding of the cameras of the Phase 1 H.E.S.S. telescopes. It employs a nitrogen laser with a pulse length of 4 ns which is used to energise a scintillator. This signal from the scintillator is then passed 50 m through multimode graded index optical fibre to the dish centre from where it illuminates uniformly the camera. Two system designs are considered. Each design would have a dish centre unit which provides a uniform light pulse for the camera calibration. The first design places the laser in the electronics hut at the telescope base, having four lasers for Phase 1, the second design has one laser in the system’s main control room with a beam-splitter and long fibre cables to guide the light to the DCUs of the Phase 1 telescopes.