Development of large size photon detectors based on THGEM and hybrid MPGD architectures

Recent progress in the development of THGEM-based photon detectors confirm the validity of this novel technology. Detectors made of THGEMs, arranged in a three layer architecture, with a CsI coating on the first layer (acting as a reflective photocathode), have been produced and operated in laboratory and during test beam runs: they provide a gain of 105 and a time resolution better than 10 ns. Improvements in the production of THGEMs with 300×300 mm² active area have recently been introduced leading to a uniform gain response and performance similar to that provided by the small area THGEMs. Promising results have been obtained by combining THGEM and Micromegas technologies to form a hybrid MPGD-based photon detector: the first prototype has proved to stably operate at large gain in a variety of gas mixtures, including pure CH₄ and to provide a low ion backflow rate. The RICH-1 detector of the COMPASS Experiment at CERN SPS will be equipped with a set of MPGD-based photon detectors replacing MWPC-based ones.