High-rate tests on Resistive Plate Chambers operated with eco-friendly gas mixtures

Results obtained by the RPC ECOgas@GIF++ Collaboration, using Resistive Plate Chambers operated with new, eco-friendly gas mixtures, based on Tetrafluoropropene and carbon dioxide, are shown and discussed in this paper. Tests aimed to assess the performance of this kind of detectors in high-irradiation conditions, analogous to the ones foreseen for the coming years at the Large Hadron Collider experiments, were performed, and demonstrate a performance basically similar to the one obtained with the gas mixtures currently in use, based on Tetrafluoroethane, which is being progressively phased out for its possible contribution to the greenhouse effect. Long term aging tests are also being carried out, with the goal to demonstrate the possibility of using these eco-friendly gas mixtures during the whole High Luminosity phase of the Large Hadron Collider.Comment: Submitted to European Physical Journal C on October 24, 2023, 15 pages, 14 figure

Performance studies of RPC detectors with new environmentally friendly gas mixtures in presence of LHC-like radiation background

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 Freon-based gas mixture containing C$_2$H$_2$F$_4$ and SF$_6$ , both greenhouse gases (GHG) with a very high global warming potential (GWP). The search of new environmentally friendly gas mixtures is necessary 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 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. The performance of RPCs were 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. 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 of GIF++ for evaluating possible long-term aging effects, gas damage due to radiation and compatibility of LHC gas system with new gases

Characterization of RPC detectors with LHC-like background radiation and new eco-friendly gas mixtures

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 $C_{2}H_{2}F_{4}$ and $SF_{6}$, 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 $C_{2}H_{2}F_{4}$ and $SF_{6}$ . In particular, HFO-1234ze has been studied as a possible replacement for $C_{2}H_{2}F_{4}$ and several gases like Novec fluoroketones, $C_{4}F_{8}O$ and $CF_{3}I$ were tested as a replacements of both $C_{2}H_{2}F_{4}$ and $SF_{6}$. 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

Measurements of fluoride production in Resistive Plate Chambers

Resistive Plate Chambers (RPCs) are operated with a gas mixture made of C$_2$H$_2$F$_4$ , SF$_6$ and iC$_4$H$_{10}$. It is well known that under the effect of a high electric field and radiation, the C2H2F4 molecule breaks into several compounds and free fluoride ions, which can accumulate under gas recirculation and could be harmful for the long-term detector operation. Furthermore, if High Pressure Laminate (HPL) electrodes are employed, the gas mixture is humidified and, in presence of water, the free fluoride ions become hydrofluoric acid (HF), a very reactive compound. The F− production depends on several factors such as radiation rate, gas flow, detector current and gas mixture. In this study we developed and tested two different set-ups for the F− concentration measurements by using an Ion Selective Electrode (ISE) station. The measurement on the F− production were performed on 2 mm gas gap bakelite RPC detector irradiated at the CERN Gamma Irradiation Facility (GIF++) with different absorption factors. Several gas mixtures were tested to understand how the formation of HF is affected. The F− production of the standard gas mixture was compared with the one of the standard gas mixture with the addition of 30% CO2 at several gamma rates. Different concentrations of SF6 were also investigated to understand if and how the SF6 could affect the F− production. Finally, two gas mixtures containing HFO1234ze, C$_2$H$_2$F$_4$ and He or CO$_2$ were used to study the RPC F− production in presence of the HFO1234ze, which is less stable in atmosphere with respect to the C$_2$H$_2$F$_4

Gas R&D; on gas recirculation and recuperation for the Resistive Plate Chamber detectors

Resistive Plate Chamber (RPC) detectors at the Large Hadron Collider (LHC) experiments are operated with a gas mixture containing C2H2F4 (R134a) and SF6. These gases are used because they allow to achieve specific detector performance. However, due to their high Global Warming Potential (GWP) they are currently subject to a phase down policy that started to affect the market with price increase and it may cause a decrease in their long-term availability. To minimize these risks, four different strategies have been identified for optimizing their usage. As immediate actions and where possible, during the LHC Long Shutdown 2 (LS2) the RPC gas systems will be upgraded to cope with new detector requirements and, in parallel, extensive campaigns for fixing leaks at detector level will be performed. Since R134a dominates the greenhouse gas consumption, the development of a R134a gas recuperation plant is going to be the next step and it might have an important positive impact on the overall optimization process. Recently a prototype system was tested with encouraging results. For future long-term detector operation, R&D; studies are ongoing for finding “green” alternatives to the currently used gases. Unfortunately, new gases developed by industry as refrigerant fluids are not behaving as the R134a in particle detectors which makes the replacement for present experiments difficult. The last strategy consists in the possibility of using industrial plants for the disposal of greenhouse gases by decomposition in harmless compounds. This solution avoids the emission in the atmosphere but it does not optimize the gas usage and problems like gas availability and price for detector operation might become the challenge in the coming years due to the greenhouse phase down policy

Studies on alternative eco-friendly gas mixtures and development of gas recuperation plant for RPC detectors

Resistive Plate Chambers (RPCs) are widely used in particle physics applications, including the CERN LHC experiments. RPCs are often operated with a gas mixture containing C$_{2}$H$_{2}$F$_{4}$ and SF$_{6}$, both greenhouse gases (GHGs) with a high global warming potential (GWP). The reduction of GHG emissions and the search for eco-friendly alternatives are crucial for use of RPCs in future since F-gases are being phased out in Europe. The best way to immediately reduce GHG emissions is to use gas recirculation systems. In parallel, CERN gas team is developing a new recuperation system specifically conceived for  C$_{2}$H$_{2}$F$_{4}$ and SF$_{6}$, where good performance has been achieved. For long-term operation, low GWP gases are studied. Hydrofluoroolefins (HFO), chlorofluorocarbons and 3M Novec are identified as possible replacements for  C$_{2}$H$_{2}$F$_{4}$ and SF$_{6}$. Several eco-friendly gas mixtures were investigated on 2 mm gap RPCs, by measuring detector performance, i.e. efficiency, streamer probability, induced charge, cluster size and time resolution. Studies were done in laboratory and at the CERN Gamma Irradiation Facility (GIF++), which provides a muon beam combined with a gamma source. Comparative analyses were performed between RPC operated with standard mixture and mixtures containing HFO with the addition of He or CO$_{2}$ or mixtures with alternatives to SF$_{6}$

Studies on impurities and F-radicals production in gaseous detectors operated with Fluorinated gas mixtures at LHC Experiments

At the CERN LHC experiments several gaseous detectors are operated with gas mixtures based on Fluorinated gases. CF$_{4}$ is used for wire chambers and Gas Electron Multiplier (GEM) detectors while C$_{2}$H$_{2}$F$_{4}$ and SF$_{6}$ for Resistive Plate Chambers (RPCs). Under the effects of electric field and radiation, these gases undergo radiolytic dissociation producing new molecules and radicals, which could be detrimental to detector long term operation. During LHC Run 2 several gas analyses were performed on the gas mixtures of RPCs and GEMs operated in ALICE, CMS and LHCb experiments. It was observed that several impurities and F-radicals are created inside the detectors and their concentration depends on several factors. Systematic studies on F-production in RPC and GEM detectors have been performed at CERN GIF++ with high background radiation. Correlations between impurities, gas flow, integrated charge, rate and detector currents were established. A comprehensive overview of the obtained results is presented

Studies of C2_{2}H2_{2}F4_{4} and SF6_{6} alternative gas mixtures for HPL RPC detectors for High Energy Physics applications

International audienceThis research investigates the viability of replacing greenhouse gases C$_{2}$H$_{2}$F$_{4}$ and SF$_{6}$ with eco-friendly gas mixtures in Resistive Plate Chamber (RPC) detectors used at CERN LHC experiments. The study focuses on the addition of CO$_{2}$ as a substitute of C$_{2}$H$_{2}$F$_{4}$ to minimize greenhouse gas emissions and reduce operational costs. Initial performance studies with cosmic muons evaluate key parameters such as efficiency, current, streamer probability, prompt charge, cluster size, and time resolution of the detectors. Subsequent assessments take place at the CERN Gamma Irradiation Facility, emulating the LHC experiment background radiation. Furthermore, the study explores alternatives to SF$_{6}$, including 3M NOVEC$^{TM}$ 4710 and AMOLEA$^{TM}$ 1224yd, presenting perforances results about these gas alternatives in High Pressure Laminate RPCs

Optimization strategies for the greenhouse gas consumption of the resistive plate chamber detectors at the CERN LHC experiments

Resistive Plate Chamber (RPC) detectors at the Large Hadron Collider (LHC) experiments are operated with a gas mixture containing two greenhouse gases (GHG): C2H2F4 (R134a) and SF6. These gases are used because they allow to achieve specific detector performance. However, due to their high Global Warming Potential (GWP) they are currently subject to a phase down policy that affects price and availability. To reduce the GHG usage, different strategies have been identified. As immediate actions, during the LHC Long Shutdown 2 (LS2) the RPC gas systems was upgraded to cope with new detector requirements and, in parallel, extensive campaigns for fixing leaks at detector level were performed. Since R134a dominates the GHG consumption, the development of a R134a gas recuperation plant is ongoing. A first prototype system was tested with encouraging results. A second prototype is under construction and it will be ready by beginning of 2023. For future long-term detector operation, R&D studies are ongoing for finding “green” alternatives to the currently used gases. Unfortunately, new gases developed by industry as refrigerant fluids are not behaving as the R134a in particle detectors which makes the replacement for present experiments difficult

Eco-friendly gas mixtures for future RPC detectors

International audienceSince a few years a joint collaboration between ALICE, ATLAS, CMS, LHCb/SHiP and CERN EP-DT groups is in place with the goal to study the performance of RPCs operated with eco-friendly gas mixtures under different irradiation conditions at GIF++.The performance of several chambers with different layout and electronics has been studied during dedicated beam tests, with and without gamma irradiation at GIF++. The RPCs have been operated with different gas mixtures based on $\rm{CO_{2}}$ and HFO1234ze gases. Results of these tests together with the future plans for aging studies of the chambers will be presented