No abstract

Since 2019 a collaboration between researchers from various institutes and experiments (i.e. ATLAS, CMS, ALICE, LHCb/SHiP and the CERN EP-DT group), has been operating several RPCs with diverse electronics, gas gap thicknesses and detector layouts at the CERN Gamma Irradiation Facility (GIF++). The studies aim at assessing the performance of RPCs when filled with new eco-friendly gas mixtures in avalanche mode and in view of evaluating possible ageing effects after long high background irradiation periods, e.g. High-Luminosity LHC phase. This challenging research is also part of a task of the European AidaInnova project. A promising eco-friendly gas identified for RPC operation is the tetrafluoruropropene (C3H2F4, commercially known as HFO-1234ze) that has been studied at the CERN GIF++ in combination with different percentages of CO2. Between the end of 2021 and 2022 several beam tests have been carried out to establish the performance of RPCs operated with such mixtures before starting the irradiation campaign for the ageing study. Results of these tests for different RPCs layouts and different gas mixtures, under increasing background rates are presented here, together with the preliminary outcome of the detector ageing tests.

Resistive Plate Chamber (RPC) detectors are widely used at the CERN LHC experiments as muon trigger thanks to their excellent time resolution. They are operated with a gas mixture containing C2H2F4 and SF6, both greenhouse gases with a very high global warming potential. The search of new environmentally friendly gas mixtures is advised to reduce GHG emissions and costs as well as to optimize RPC performance. Several recently available gases with low GWP have been identified as possible replacements for C2H2F4 and SF6. In particular, HFO-1234ze has been studied as a possible replacement for C2H2F4 and several gases like Novec fluoroketones, C4F8O and CF3I were tested as a replacements of both C2H2F4 and SF6. The RPC detectors have been tested in laboratory conditions and few selected mixtures were tested at the CERN Gamma Irradiation Facility, which provides a high energy muon beam combined with an intense gamma source allowing to simulate the background expected at HL-LHC . The performance of RPCs was studied at different gamma rates in a presence of muon beam by measuring efficiency, streamer probability, rate capability, induced charge and cluster size. The studies are being carried on by operating RPCs under gas recirculation with the selected gas mixture and exposed to the intense gamma radiation of GIF++ for evaluating possible long-term aging effects, gas damage due to radiation and compatibility of LHC gas system with new gases.

A wide range of gas mixtures is used for the operation of the gaseous detectors at the CERN LHC experiments. Some gases, as C2H2F4, CF4, C4F10 and SF6, are greenhouse gases (GHG) with high global warming potential and therefore subject to a phase down policy. The reduction of GHG emissions is of paramount importance for CERN, which has identified four different strategies. The first strategy is based on the optimization of the gas mixture recirculation plants already in use. The second approach is the recuperation of used gas mixtures followed by separation of the GHG for its re-use. Several R&D are ongoing to evaluate this possibility and prepare the design of final systems. A third approach is making use of industrially available solutions for disposal of GHGs. Finally, the search of new eco-friendly gases is object of many R&D programs by the detector communities. The four strategies will be compared by considering investment required, return benefit and technological readiness.

Resistive Plate Chamber (RPC) detectors are widely used thanks to their excellent time resolution and low production cost. At the CERN LHC experiments, the large RPC systems are operated in avalanche mode thanks to a Freon-based gas mixture containing C 2 H 2 F 4 and SF 6 , both greenhouse gases with a very high global warming potential (GWP). The search of new environmentally friendly gas mixtures is advisable for reducing greenhouse gas emissions, costs as well as to optimize RPC performance and possible detector aging issues. Several hydrofluorocarbons, hydrofluoroolefins (HFOs) and innovative industrial alternative to SF 6 gases with very low GWP have been identified as possible replacements of C 2 H 2 F 4 and SF 6 . More than 60 environmentally friendly gas mixtures have been investigated on 2 mm single-gap RPCs. The RPC detectors have been tested in laboratory conditions and at the CERN Gamma Irradiation Facility (GIF++), which provides a high energy muon beam combined with an intense gamma source allowing to simulate the background expected at HL-LHC. RPCs performance have been studied at different gamma rates with the new environmentally friendly gases by measuring efficiency, streamer probability, rate capability, induced charge, cluster size and time resolution. Encouraging results of RPC operation in avalanche mode have been obtained with 4 and 5 components gas mixtures. To finalize the studies, the RPCs are now operated under gas recirculation with the selected new gas mixture and exposed to the intense gamma radiation at the CERN GIF++ facility for evaluating possible long-term aging effects, gas damage due to radiation and compatibility of LHC gas system with new gases.