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The design of a Ring Imaging CHerenkov (RICH) detector for the identification of high momentum particles at the future Electron Ion Collider (EIC) is extremely challenging by using current technology. Compact collider setups impose to construct RICH with short radiator length, hence limiting the number of generated photons. The number of detected photons can be increased by selecting the far UV region. As standard fused-silica windows is opaque below 165 nm, a windowless RICH can be a possible approach. CsI is widely used photocathode (PC) for photon detection in the far UV range. Due to its hygroscopic nature it is very delicate to handle. In addition, its Quantum Efficiency (QE) degrades in high intensity ion fluxes. These are the key reasons to quest for novel PC with sensitivity in the far UV region. Recent development of layers of hydrogenated nanodiamond powders as an alternative PC material and their performance, when coupled to the THick Gaseous Electron Multipliers (THGEM)-based detectors, are the objects of an ongoing R\&D. We report here some preliminary results on the initial phase of these studies., 6 pages, 5 figures, MPGD-2019 La Rochelle, Proceeding

The RICH detector of the COMPASS Experiment at CERN SPS is undergoing an important upgrade: the central MWPC-based photon detectors have been replaced with novel Micropattern detectors, to cope with the challenging efficiency and stability requirements of the new COMPASS measurements. The new hybrid MPGD detector consists of two layers of ThickGEMs and a capacitive bulk Micromegas. Photoconversion takes place on the CsI layer deposited onto the first ThickGEM, while position information and signals are read out from the pad-segmented anode via capacitive coupling by analog front-end electronics based on APV25 chips. The paper focuses on the main issues of production, detailed quality assessment technique, and the commissioning status of the first in-experiment MPGD-based photon detectors for RICH application.

In the context of a project to upgrade the gas photon detectors of COMPASS RICH-1, we have performed an R&D programme aimed to develop photon detectors based on multi-layer arrangements of thick GEM electron multipliers coupled to a CsI photoconverter. For this purpose, thick GEMs have been characterised in detail including the gain performance, its dependance on the geometrical parameters and its time-evolution, a feature exhibited by the gas detectors with open insulator surfaces. The variation due to this evolution drammatically depends on the parameters themselves. In the present article we summarise the outcomes of the studies dedicated to the thick GEM gain and its evolution versus time. We also include a qualitative model which accounts for the peculiar details of the observed thick GEM gain time-evolution.

Photon detectors based on micropattern gas detectors represent a new generation of gaseous photon detectors. In the context of a project to upgrade the gas photon detectors of COMPASS RICH-1, we are performing an R&D programme aimed both to establish the principles and to develop the engineering aspects of photon detectors based on multi-layer arrangements of thick GEMs electron multipliers coupled to a CsI photoconverter. In this context, a reduced rate of the backflow of the positive ions generated in the multiplication process is required to overcome the critical issues related to the bombardment of the CsI photoconverter by ions. Our studies devoted to develop detector architectures able to provide reduced ion backflow rates are reported.

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.

The development of a large size gaseous detector of single photons, able to stably operate at high gain and high rate, and to provide good time resolution and insensitivity to magnetic field would be beneficial to future Cherenkov Imaging Counters. The detector could be based on the use of a multilayer architecture of THGEM electron multipliers coupled to a solid state CsI photocathode. A systematic study of the response of THGEM-based counters versus the geometrical parameters has been performed and the main results will be presented. Small photon detector prototypes have been built and preliminary data obtained detecting single photoelectrons are presented as well. The key aspect of photoelectron extraction from the photocathode is illustrated presenting both simulation and dedicated measurement results. © 2010 IOP Publishing Ltd and SISSA