Abstract
In fundamental research, gas detectors of single photons are a must in the field of Cherenkov imaging techniques (RICH counters) for particle identification in large momentum ranges and with wide coverage of the phase space domain. These counters, already extensively used, are foreseen in the setups of future experiments in a large variety of fields in nuclear and particle physics. The quest of novel gaseous photon detector is dictated by the fact that the present generation of detectors has unique characteristics concerning operation in magnetic field, low material budget and cost, but it suffers of severe limitations in effective efficiency, rates, life time and stability, discouraging their use in high precision and high rate experiments. We are developing large size THick GEM (THGEM)-based detector of single photons. The R&D program includes the complete characterization of the THGEM electron multipliers, the study of the aspects related to the detection of single photons and the engineering towards large size detector prototype. Our most recent achievements include: dedicated studies concerning the ion back-flow to the photo-cathode; relevant progress in the engineering aspects, in particular related to the production of large-size THGEMs, where the strict correlation between the local gain-value and the local thickness-value has been demonstrated the operation of a 300 mm × 300 mm2 active area detector at the CERN PS T10 test beam; the introduction of a new hybrid detector architecture offering promising indication, which is formed by a THGEM layer which acts as CsI support and pre-amplification device followed by a MICROMEGAS multiplication stage. The general status of the R&D program and the recent progress are reported
Highlights
Within the RD51 collaboration, which aims to the development of Micro Pattern Gaseous Detector technologies, in 2009 we have started an intense R&D activity aiming to pin out the best candidate to improve COMPASS RICH-1 detector capabilities by replacing the MWPC based photon detector system with a new technology
It is clear that the critical issue of the photon feedback can find a potential solution in the use of a closed geometry structure, where the photo converting layer can not be reached by the photons generated in the multiplication process, in addition with a multilayer structure of electron multipliers a good fraction of the ions can be trapped by the intermediate layers provided the proper choice of the electric fields; the possibility to use several multiplication stages allows for high gain operation
The possibility to produce large size devices at affordable cost despite the few millions holes per square meter, their intrinsic mechanical stiffness, their robustness against damages produced by electrical discharges and the possibility to operate them in magnetic field thanks to the reduced gaps between each multiplier stage, are the appealing features that persuaded us to their use as single photon detector candidates for the RICH-1 upgrade
Summary
Within the RD51 collaboration, which aims to the development of Micro Pattern Gaseous Detector technologies, in 2009 we have started an intense R&D activity aiming to pin out the best candidate to improve COMPASS RICH-1 detector capabilities by replacing the MWPC based photon detector system with a new technology. A THGEM based photon detector does not suffer from photon feedback while the ions generated in the multiplication process can reach the photocathode surface following back the electric field lines. Comparing the two extreme configurations: completely aligned and completely misaligned holes of THGEM2, for the same biasing electrode voltage the effective gain is reduced by 40% [15]. This gain loss can be recovered increasing the voltage across the last THGEM multiplier stage
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