Light-Trap · A SiPM upgrade for VHE Astronomy and beyond

A SiPM upgrade for VHE Astronomy and beyond

"Ground-based gamma-ray astronomy in the Very High Energy (VHE, E>100 GeV) regime has fast become one of the most interesting and productive sub-fields of astrophysics today. Also known as VHE Astronomy, it utilizes the Imaging Atmospheric Cherenkov Technique (IACT) to detect Cherenkov radiation (UV/Blue dominated) that has been emitted by Extensive Air Showers produced by gamma-ray photons interacting in the upper atmosphere. Research and development of new and improved technology for increasing the light-collection efficiency and field-of-view (FOV) of the camera systems used in VHE astronomy is always on going. These improvements can also allow for the consideration of an increase in the number of telescopes used in an array, if the cost of the cameras could be significantly reduced. The primary path to these goals is to replace Photomultiplier Tubes (PMTs) with Silicon-PMs (SiPMs) that have substantially larger collection area than those currently on the market. These large-area SiPMs would also find multi-disciplinary uses e.g. in fluorescence telescopes for detection of Ultra High Energy Cosmic Rays and medical physics. This project was targeted at increasing the physical area and sensitivity of SiPMs by attaching one to a “Light-Trap” disk. This Light-Trap disk will need to collect light over an area much larger than the SiPM itself, be sensitive to wavelengths where signal dominates over background and be much cheaper than the SiPM. Here we propose a novel method to build relatively low-cost SiPM-based pixels utilizing wavelength-shifting (WLS) material (through a scintillating PMMA disk). We optimized the design of such a pixel, integrated them in an actual 7-pixel cluster that was installed into a camera on one of the MAGIC VHE telescopes and tested during real observations. The device boosted the sensitivity of a commercially available SiPM to UV light, while being essentially blind to longer wavelengths, and performed excellently under real-world conditions. With some future improvements to the proof-of-concept design, it is feasible that large-scale cameras with UV-sensitive ""Light-Trap"" pixels could be produced, reducing camera costs while increasing FOV and maintaining scientific performance. "

Data: CORDIS, © European Union