Speaker
Description
The Large Size Telescope (LST) is the largest telescope of the Cherenkov Telescope Array project, with a diameter of 23m and a focal plane instrumentation of 4 square meters. In the current design, it comprises cameras equipped with arrays of 1855 photomultiplier tubes (PMTs). Each PMT has a light concentrator in front to reduce the stray light as well as to reduce the dead space between PMTs. These cameras are built to detect the nanosecond flashes of Cherenkov light from atmospheric air showers generated by gamma rays entering the atmosphere. Thanks to rapid development, silicon photomultipliers (SiPMs) are becoming valid and economical alternatives to PMTs in several fields, due to their lower operating voltage, larger photon efficiency, reduced ageing and insensitivity to magnetic fields. These properties make SiPMs suitable for gamma-ray astronomy and for imaging atmospheric Cherenkov telescopes. Here we discuss a minimal-effort scenario for an upgrade of an LST PMT-based camera to a SiPM-based camera, in which most of the hardware is maintained. Thanks to a ray-tracing software, we show that the minimal valid solution consists of replacing each PMT by several SiPMs. In particular, the existing light funnel in front of each pixel does not have to be exchanged considering the angular distribution of light at the SiPM surface and its angular response. We briefly discuss the effect on the sensitivity of the instrument of an upgrade to SiPMs.
