Performance studies on Resistive Plate Chambers detectors operated with new environmentally friendly gas mixtures at CERN GIF++ facility

Resistive Plate Chamber (RPC) detectors are widely used at CERN LHC experiments as a muon trigger due 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 high Global Warming Potential (GWP) and therefore subject to European regulations aiming at reducing the GHG emissions. Alternative gases in the HydroFluoroOlefin (HFO) family have already been identified by the industry as a low GWP replacement of the $C_2 H_2 F_4$. The search of new environmental friendly gas mixtures is advisable for reducing greenhouse gas emissions, costs as well as optimize RPC performance and possible detector aging issues. The aim of this study is to characterize the RPC detector operation using low GWP gas mixtures based on HFO and compare the results with the standard gas mixture ($C_2 H_2 F_4$/$i C_4 H_{10}$/$SF_6$ - 95.2/4.5/0.3) used at the ATLAS and CMS experiments. The RPC detectors were tested in laboratory conditions and at the CERN Gamma Irradiation Facility (GIF++), which provides a high energy muon beam from the SPS combined with an intense gamma source, allowing to simulate the background radiation expected at the High Luminosity LHC Phase (HL-LHC). Firstly, several eco-friendly gas mixtures were tested on a dedicated experimental setup in laboratory. A five component gas mixture (HFO-1234ze/$C_2 H_2 F_4$/$CO_2$/$SF_6$/$i C_4 H_{10}$) was selected as a suitable candidate for its low GWP and for giving good detector performance comparable with the currently used mixture at LHC experiments. The setup was then moved to the GIF++ to validate the operation of RPC at high gamma rate with the selected gas mixture. At the GIF++, the RPC detectors were studied with different muon and gamma background rates in terms of efficiency, streamer probability, induced charge, cluster size, and rate capability. The results indicate that the use of HFO based mixtures lead to a working point shifted of 1000V towards higher voltage and a streamer probability at the efficiency knee higher than the one with the standard gas mixture. The RPC operated with the HFO based gas mixture proved to have efficiency versus rate curves comparable to the standard gas mixture, indicating a rate capability suitable for the background rate expected at HL-LHC. However, the higher streamer probability could induce long term ageing effects that are now under evaluation

Études visant à réduire les émissions de gaz à effet serre émis par les détecteurs de particules des expériences LHC du CERN

Une large gamme de mélanges gazeux est utilisée pour le fonctionnement de différents dé-tecteurs à gaz dans les expériences LHC du CERN. Certains de ces gaz, notamment C2H2F4, CF4, SF6 et C4F10, sont classifiés parmi les gaz à effet de serre (GHG) à fort potentiel de ré-chauffement planétaire (GWP) et soumis donc à une politique de réduction progressive de leurs prix et de leur disponibilité sur le marché. Ces gaz sont responsables de 70% des émis-sions GHG directes provenant du fonctionnement du CERN. L’objectif de l’Organisation est de réduire ces émissions de 28% d’ici à la fin de 2024 (année de référence : 2018). Le présent travail montre le développement de deux stratégies de recherche définies par le groupe gaz du CERN pour réduire les émissions GHG. Dans la mesure du possible, les détecteurs de grand volume sont exploités avec des systèmes de recirculation des gaz, reu-tilisant jusqu’à 90 % de ceux-ci. Ce travail de thèse se concentre sur l’optimisation des tech-nologies de système à gaz existantes afin d’améliorer les performances d’exploitation et de permettre une réduction supplémentaire de la consommation. En particulier, des logiciels de surveillance ont été spécialement conçues pour régler correctement les parties de contrôle des différents modules des systèmes à gaz. En outre, des pipelines d’analyse de données spécifiques ont été développés pour évaluer la performance d’un système à gaz et pour sur-veiller les consommations. Un deuxième axe de recherche examiné dans ce travail consiste en l’étude des performances des détecteurs RPC avec l’utilisation de gaz alternatifs. Les RPCs des expériences ATLAS et CMS fonctionnent actuellement avec un mélange gazeux à trois composants, principalement basé sur le C2H2F4 (GWP100 = 1430), environ 5 % de i-C4H10, et de 0,3 % de SF6 (GWP100 = 22800). En raison de la présence de fuites au niveau des détecteurs, le C2H2F4 domine l’ensemble des émissions GHG du CERN. Une alternative à ce gaz pourrait-être le R-1234ze, une molécule appartenant à la famille des Hydro-Fluoro-Olefins (HFO) avec un GWP100 de 7, tandis que des alternatives au SF6 ont été trouvées parmi les gaz de la famille Novec (Novec™ 4710 et Novec™ 5110), C4F8O, CF3I et Amolea™ 1224yd. Les performances des RPC avec des mélanges de gaz basés sur des gaz alternatifs ont d’abord été évaluées en laboratoire en étudiant l’efficacité du détecteur, les courants, la probabilité de formation de streamers, la charge, la cluster size et la résolution temporelle. Quelques mélanges de gaz sélectionnés ont ensuite été testés dans la Gamma Irradiation Facility du CERN qui fournit un faisceau de muons et un rayonnement gamma de fond, permettant de simuler les conditions de rayonnement du HL-LHC. Quelques mélanges ga-zeux ont montré des performances similaires en termes de rate de détection par rapport au mélange standard. Des études de performance à long terme ont été lancées et des études préliminaires sur la production d’impuretés dans les mélanges gazeux à base de HFO sont présentées dans ce travail, mettant en évidence que la molécule R-1234ze produit environ dix fois plus d’ions F- que la molécule C2H2F4.A wide range of gas mixtures is used to operate different gaseous detectors at the CERN LHC experiments. Some of these gases, namely C2H2F4, CF4, SF6, C4F10, are classified as Greenhouse Gases (GHG) with a high Global Warming Potential, therefore subjected to a phase-down policy affecting their price and market availability. These gases are respon-sible for 70% of CERN particle detector operation’s direct greenhouse gas emissions. The Organisation’s objective is to reduce such emissions by 28% by the end of 2024 (baseline year: 2018). The present work shows the development of two main research strategies delineated by the CERN gas group to reduce GHG emissions. Wherever suitable, large detector volumes are operated with recirculating gas systems. The first part of this thesis focuses on optimizing existing gas system technologies to improve operating performances and further reduce gas consumption. In particular, dedicated monitoring infrastructures were designed to properly tune the active control parts of the different gas modules. Fur-thermore, specific data analysis pipelines were developed to evaluate a gas system’s per-formance and monitor gas consumption. A second research line examined in this work consisted of studying the performance of RPC detectors operated with eco-friendly gases. RPCs at ATLAS and CMS experiments are operated with a three-component gas mixture mainly based on C2H2F4 (R-134a, GWP100 = 1430), around 5% of i-C4H10, and a minor frac-tion of 0.3% of SF6 (GWP100 = 22800). Due to the presence of leaks at the detector level, C2H2F4 dominates the overall CERN GHG emissions. Alternatives to C2H2F4 were identi-fied in R-1234ze, a molecule in the family of HydroFluoroOlefins with a GWP100 = 7, while SF6 alternatives were found in the Novec family (Novec™ 4710 and Novec™ 5110), C4F8O, CF3I, and Amolea™ 1224yd. RPC performance with gas mixtures based on alternative gases was firstly evaluated in laboratory conditions by studying the detector’s efficiency, currents, streamer probability, prompt charge, cluster size, and time resolution. Few selected gas mix-tures were then tested at the Gamma Irradiation Facility, which provides muon beam and gamma background radiation, allowing to emulate the High Luminosity LHC background conditions. Few gas mixtures showed similar rate capability performance with respect to the standard gas mixture. Long-term performance studies were started, and preliminary studies on impurities productions for HFO-based gas mixtures are presented, showing the R-1234ze molecule produces an order of magnitude more F− ions than the C2H2F4 one

Studies to reduce greenhouse gases emissions from particles detectors operation at the CERN LHC experiments

A wide range of gas mixtures is used to operate different gaseous detectors at the CERN LHC experiments. Some of these gases, namely C$_2$H$_2$F$_4$, CF$_4$, SF$_6$, C$_4$F$_{10}$, are classified as Greenhouse Gases (GHG) with a high Global Warming Potential, therefore subjected to a phase-down policy affecting their price and market availability. These gases are responsible for 70\% of CERN particle detector operation’s direct greenhouse gas emissions. The Organisation’s objective is to reduce such emissions by 28\% by the end of 2024 (baseline year: 2018). The present work shows the development of two main research strategies delineated by the CERN gas group to reduce GHG emissions. Wherever suitable, large detector volumes are operated with recirculating gas systems. The first part of this thesis focuses on optimizing existing gas system technologies to improve operating performances and further reduce gas consumption. In particular, dedicated monitoring infrastructures were designed to properly tune the active control parts of the different gas modules. Furthermore, specific data analysis pipelines were developed to evaluate a gas system’s performance and monitor gas consumption. A second research line examined in this work consisted of studying the performance of RPC detectors operated with eco-friendly gases. RPCs at ATLAS and CMS experiments are operated with a three-component gas mixture mainly based on C$_2$H$_2$F$_4$ (R-134a, GWP$_{100}$ = 1430), around 5\% of \isobutane, and a minor fraction of 0.3\% of SF$_6$ (GWP$_{100}$ = 22800). Due to the presence of leaks at the detector level, C$_2$H$_2$F$_4$ dominates the overall CERN GHG emissions. Alternatives to C$_2$H$_2$F$_4$ were identified in R-1234ze, a molecule in the family of HydroFluoroOlefins with a GWP$_{100}$ = 7, while SF$_6$ alternatives were found in the Novec family (Novec™ 4710 and Novec™ 5110), C$_4$F$_8$O, CF$_3$I, and Amolea™ 1224yd. RPC performance with gas mixtures based on alternative gases was firstly evaluated in laboratory conditions by studying the detector’s efficiency, currents, streamer probability, prompt charge, cluster size, and time resolution. Few selected gas mixtures were then tested at the Gamma Irradiation Facility, which provides muon beam and gamma background radiation, allowing to emulate the High Luminosity LHC background conditions. Few gas mixtures showed similar rate capability performance with respect to the standard gas mixture. Long-term performance studies were started, and preliminary studies on impurities productions for HFO-based gas mixtures are presented, showing the R-1234ze molecule produces an order of magnitude more F$^{-}$ ions than the C$_2$H$_2$F$_4$ one

Études visant à réduire les émissions de gaz à effet serre émis par les détecteurs de particules des expériences LHC du CERN

A wide range of gas mixtures is used to operate different gaseous detectors at the CERN LHC experiments. Some of these gases, namely C2H2F4, CF4, SF6, C4F10, are classified as Greenhouse Gases (GHG) with a high Global Warming Potential, therefore subjected to a phase-down policy affecting their price and market availability. These gases are respon-sible for 70% of CERN particle detector operation’s direct greenhouse gas emissions. The Organisation’s objective is to reduce such emissions by 28% by the end of 2024 (baseline year: 2018). The present work shows the development of two main research strategies delineated by the CERN gas group to reduce GHG emissions. Wherever suitable, large detector volumes are operated with recirculating gas systems. The first part of this thesis focuses on optimizing existing gas system technologies to improve operating performances and further reduce gas consumption. In particular, dedicated monitoring infrastructures were designed to properly tune the active control parts of the different gas modules. Fur-thermore, specific data analysis pipelines were developed to evaluate a gas system’s per-formance and monitor gas consumption. A second research line examined in this work consisted of studying the performance of RPC detectors operated with eco-friendly gases. RPCs at ATLAS and CMS experiments are operated with a three-component gas mixture mainly based on C2H2F4 (R-134a, GWP100 = 1430), around 5% of i-C4H10, and a minor frac-tion of 0.3% of SF6 (GWP100 = 22800). Due to the presence of leaks at the detector level, C2H2F4 dominates the overall CERN GHG emissions. Alternatives to C2H2F4 were identi-fied in R-1234ze, a molecule in the family of HydroFluoroOlefins with a GWP100 = 7, while SF6 alternatives were found in the Novec family (Novec™ 4710 and Novec™ 5110), C4F8O, CF3I, and Amolea™ 1224yd. RPC performance with gas mixtures based on alternative gases was firstly evaluated in laboratory conditions by studying the detector’s efficiency, currents, streamer probability, prompt charge, cluster size, and time resolution. Few selected gas mix-tures were then tested at the Gamma Irradiation Facility, which provides muon beam and gamma background radiation, allowing to emulate the High Luminosity LHC background conditions. Few gas mixtures showed similar rate capability performance with respect to the standard gas mixture. Long-term performance studies were started, and preliminary studies on impurities productions for HFO-based gas mixtures are presented, showing the R-1234ze molecule produces an order of magnitude more F− ions than the C2H2F4 one.Une large gamme de mélanges gazeux est utilisée pour le fonctionnement de différents dé-tecteurs à gaz dans les expériences LHC du CERN. Certains de ces gaz, notamment C2H2F4, CF4, SF6 et C4F10, sont classifiés parmi les gaz à effet de serre (GHG) à fort potentiel de ré-chauffement planétaire (GWP) et soumis donc à une politique de réduction progressive de leurs prix et de leur disponibilité sur le marché. Ces gaz sont responsables de 70% des émis-sions GHG directes provenant du fonctionnement du CERN. L’objectif de l’Organisation est de réduire ces émissions de 28% d’ici à la fin de 2024 (année de référence : 2018). Le présent travail montre le développement de deux stratégies de recherche définies par le groupe gaz du CERN pour réduire les émissions GHG. Dans la mesure du possible, les détecteurs de grand volume sont exploités avec des systèmes de recirculation des gaz, reu-tilisant jusqu’à 90 % de ceux-ci. Ce travail de thèse se concentre sur l’optimisation des tech-nologies de système à gaz existantes afin d’améliorer les performances d’exploitation et de permettre une réduction supplémentaire de la consommation. En particulier, des logiciels de surveillance ont été spécialement conçues pour régler correctement les parties de contrôle des différents modules des systèmes à gaz. En outre, des pipelines d’analyse de données spécifiques ont été développés pour évaluer la performance d’un système à gaz et pour sur-veiller les consommations. Un deuxième axe de recherche examiné dans ce travail consiste en l’étude des performances des détecteurs RPC avec l’utilisation de gaz alternatifs. Les RPCs des expériences ATLAS et CMS fonctionnent actuellement avec un mélange gazeux à trois composants, principalement basé sur le C2H2F4 (GWP100 = 1430), environ 5 % de i-C4H10, et de 0,3 % de SF6 (GWP100 = 22800). En raison de la présence de fuites au niveau des détecteurs, le C2H2F4 domine l’ensemble des émissions GHG du CERN. Une alternative à ce gaz pourrait-être le R-1234ze, une molécule appartenant à la famille des Hydro-Fluoro-Olefins (HFO) avec un GWP100 de 7, tandis que des alternatives au SF6 ont été trouvées parmi les gaz de la famille Novec (Novec™ 4710 et Novec™ 5110), C4F8O, CF3I et Amolea™ 1224yd. Les performances des RPC avec des mélanges de gaz basés sur des gaz alternatifs ont d’abord été évaluées en laboratoire en étudiant l’efficacité du détecteur, les courants, la probabilité de formation de streamers, la charge, la cluster size et la résolution temporelle. Quelques mélanges de gaz sélectionnés ont ensuite été testés dans la Gamma Irradiation Facility du CERN qui fournit un faisceau de muons et un rayonnement gamma de fond, permettant de simuler les conditions de rayonnement du HL-LHC. Quelques mélanges ga-zeux ont montré des performances similaires en termes de rate de détection par rapport au mélange standard. Des études de performance à long terme ont été lancées et des études préliminaires sur la production d’impuretés dans les mélanges gazeux à base de HFO sont présentées dans ce travail, mettant en évidence que la molécule R-1234ze produit environ dix fois plus d’ions F- que la molécule C2H2F4

Études visant à réduire les émissions de gaz à effet serre émis par les détecteurs de particules des expériences LHC du CERN

A wide range of gas mixtures is used to operate different gaseous detectors at the CERN LHC experiments. Some of these gases, namely C2H2F4, CF4, SF6, C4F10, are classified as Greenhouse Gases (GHG) with a high Global Warming Potential, therefore subjected to a phase-down policy affecting their price and market availability. These gases are respon-sible for 70% of CERN particle detector operation’s direct greenhouse gas emissions. The Organisation’s objective is to reduce such emissions by 28% by the end of 2024 (baseline year: 2018). The present work shows the development of two main research strategies delineated by the CERN gas group to reduce GHG emissions. Wherever suitable, large detector volumes are operated with recirculating gas systems. The first part of this thesis focuses on optimizing existing gas system technologies to improve operating performances and further reduce gas consumption. In particular, dedicated monitoring infrastructures were designed to properly tune the active control parts of the different gas modules. Fur-thermore, specific data analysis pipelines were developed to evaluate a gas system’s per-formance and monitor gas consumption. A second research line examined in this work consisted of studying the performance of RPC detectors operated with eco-friendly gases. RPCs at ATLAS and CMS experiments are operated with a three-component gas mixture mainly based on C2H2F4 (R-134a, GWP100 = 1430), around 5% of i-C4H10, and a minor frac-tion of 0.3% of SF6 (GWP100 = 22800). Due to the presence of leaks at the detector level, C2H2F4 dominates the overall CERN GHG emissions. Alternatives to C2H2F4 were identi-fied in R-1234ze, a molecule in the family of HydroFluoroOlefins with a GWP100 = 7, while SF6 alternatives were found in the Novec family (Novec™ 4710 and Novec™ 5110), C4F8O, CF3I, and Amolea™ 1224yd. RPC performance with gas mixtures based on alternative gases was firstly evaluated in laboratory conditions by studying the detector’s efficiency, currents, streamer probability, prompt charge, cluster size, and time resolution. Few selected gas mix-tures were then tested at the Gamma Irradiation Facility, which provides muon beam and gamma background radiation, allowing to emulate the High Luminosity LHC background conditions. Few gas mixtures showed similar rate capability performance with respect to the standard gas mixture. Long-term performance studies were started, and preliminary studies on impurities productions for HFO-based gas mixtures are presented, showing the R-1234ze molecule produces an order of magnitude more F− ions than the C2H2F4 one.Une large gamme de mélanges gazeux est utilisée pour le fonctionnement de différents dé-tecteurs à gaz dans les expériences LHC du CERN. Certains de ces gaz, notamment C2H2F4, CF4, SF6 et C4F10, sont classifiés parmi les gaz à effet de serre (GHG) à fort potentiel de ré-chauffement planétaire (GWP) et soumis donc à une politique de réduction progressive de leurs prix et de leur disponibilité sur le marché. Ces gaz sont responsables de 70% des émis-sions GHG directes provenant du fonctionnement du CERN. L’objectif de l’Organisation est de réduire ces émissions de 28% d’ici à la fin de 2024 (année de référence : 2018). Le présent travail montre le développement de deux stratégies de recherche définies par le groupe gaz du CERN pour réduire les émissions GHG. Dans la mesure du possible, les détecteurs de grand volume sont exploités avec des systèmes de recirculation des gaz, reu-tilisant jusqu’à 90 % de ceux-ci. Ce travail de thèse se concentre sur l’optimisation des tech-nologies de système à gaz existantes afin d’améliorer les performances d’exploitation et de permettre une réduction supplémentaire de la consommation. En particulier, des logiciels de surveillance ont été spécialement conçues pour régler correctement les parties de contrôle des différents modules des systèmes à gaz. En outre, des pipelines d’analyse de données spécifiques ont été développés pour évaluer la performance d’un système à gaz et pour sur-veiller les consommations. Un deuxième axe de recherche examiné dans ce travail consiste en l’étude des performances des détecteurs RPC avec l’utilisation de gaz alternatifs. Les RPCs des expériences ATLAS et CMS fonctionnent actuellement avec un mélange gazeux à trois composants, principalement basé sur le C2H2F4 (GWP100 = 1430), environ 5 % de i-C4H10, et de 0,3 % de SF6 (GWP100 = 22800). En raison de la présence de fuites au niveau des détecteurs, le C2H2F4 domine l’ensemble des émissions GHG du CERN. Une alternative à ce gaz pourrait-être le R-1234ze, une molécule appartenant à la famille des Hydro-Fluoro-Olefins (HFO) avec un GWP100 de 7, tandis que des alternatives au SF6 ont été trouvées parmi les gaz de la famille Novec (Novec™ 4710 et Novec™ 5110), C4F8O, CF3I et Amolea™ 1224yd. Les performances des RPC avec des mélanges de gaz basés sur des gaz alternatifs ont d’abord été évaluées en laboratoire en étudiant l’efficacité du détecteur, les courants, la probabilité de formation de streamers, la charge, la cluster size et la résolution temporelle. Quelques mélanges de gaz sélectionnés ont ensuite été testés dans la Gamma Irradiation Facility du CERN qui fournit un faisceau de muons et un rayonnement gamma de fond, permettant de simuler les conditions de rayonnement du HL-LHC. Quelques mélanges ga-zeux ont montré des performances similaires en termes de rate de détection par rapport au mélange standard. Des études de performance à long terme ont été lancées et des études préliminaires sur la production d’impuretés dans les mélanges gazeux à base de HFO sont présentées dans ce travail, mettant en évidence que la molécule R-1234ze produit environ dix fois plus d’ions F- que la molécule C2H2F4

Studies on RPC detectors operated with environmentally friendly gas mixtures in LHC-like conditions

Resistive Plate Chambers (RPC) are gaseous detectors employed at CERN LHC experiments thanks to their trigger performance, timing capabilities and contained production costs. High Pressure Laminate RPCs are operated with a three-component gas mixture, made of 90%–95% of C2H2F4, around 5% of i-C4H10 and 0.3% of SF6. Due to the presence of leaks at detector level and to the greenhouse characteristics of C2H2F4 and SF6, RPCs in ATLAS and CMS were accounting for about 87% of CO2 equivalent emissions during LHC Run 2. The addition of some amount of CO2 into the RPCs gas mixture was explored as a possible short-to-medium term solution to lower the total greenhouse gases emissions and reduce the usage of C2H2F4. A dedicated data taking campaign was performed at the Gamma Irradiation Facility at CERN, where RPCs detectors performance were studied with muon beam and gamma background. The detectors were operated with the addition of 30% and 40% of CO2 to the standard gas mixture, together with an increased fraction of SF6. In addition, the performance with two different amount of i-C4H10 were evaluated in order to assess the compatibility of the gas mixture with the CMS and ATLAS requirements. Results on the muon beam performance of RPCs operated with the aforementioned gas mixtures are reported in this work

Gas recirculation systems for RPC detectors: From LHC experiments to laboratory set-ups

The Resistive Plate Chamber (RPC) detectors are extensively used worldwide and at CERN LHC experiments thanks to their excellent time resolution and low cost. RPCs are often operated with a humidified gas mixture made of C2H2F4, SF6 and i-C4H10. Unfortunately, C2H2F4 and SF6 are greenhouse gases (GHGs) with a global warming potential (GWP) of 1430 and 22800 respectively and they are subject to a phase-down policy in Europe (EU F-gas regulation). It is therefore foreseeable that F-gases availability would be uncertain for the future and their price could raise possibly making gas detectors operation very costly. The reduction of GHG emissions is an objective of paramount importance for CERN and four different strategies have been identified to achieve it. One of these strategies is based on the use of gas recirculation systems. This solution is already implemented in all gas systems supplying gaseous mixtures to the CERN LHC detectors. These recirculation systems are complex and sophisticated apparatus for big detector volumes (tens to hundreds of m3) that extend from surface to underground cavern and they are controlled through an industrial Programmable Logic Controller (PLC). Their cost is considerable and therefore they are used for large detector apparatus. In order to cope with the increase of small experiments and detector facilities, the CERN gas team has developed two new portable gas recirculation systems at affordable cost. The first gas recirculation unit can be used for several detectors connected in series or parallel flushed with hundreds of liters per hour. It is controlled though a small PLC and it can regulate detector pressure at the level of the mbar. Some of these gas recirculation systems are already in use since several years at CERN GIF++ facility for CSC, GEM and RPC detectors. A second gas recirculation unit has been developed for laboratory purpose where one or two detectors are flushed with few liters per hour. In this case, the unit has to be very cheap and user-friendly in order to allow an easy operation from the final user. Both portable gas recirculation systems can be easily adapted for the different types of detector systems and set-ups thanks to their low price, flexibility and user-friendly operation. An overview of the LHC, medium and small gas recirculation systems will be given in this contribution

Performance studies of RPC detectors operated with C2_2H2_2F4_4 and CO2_2 gas mixtures

Resistive Plate Chambers detectors are largely employed at the CERN LHC experiments thanks to their excellent trigger performances and contained costs. They are operated with a gas mixture made of 90%–95% of C2H2F4, that provides a high number of ion–electron pairs, about 5% of i-C4H10, that ensures the suppression of photon-feedback effects, and 0.3% of SF6, used as an electron quencher to further operate the detector in streamer-free mode. C2H2F4is known to be a Greenhouse gas, with a global warming potential (GWP) of 1430. CERN has identified several strategies to reduce the consumption of greenhouse gas emissions from particle detectors at LHC experiments. One research line is focused on the study of alternatives to C2H2F4. In this context, a conservative approach for the next years of LHC operation could be to focus on reducing the GWP of the RPC gas mixture by only adding CO2 and not using new gases, whose effects on detector long-term operation have to be studied. The RPC performance with standard gas mixture with the addition of 30%–50% of CO2 (and SF6 concentration between 0.3 and 0.9%) were studied both in laboratory set-up and at the CERN Gamma Irradiation Facility in presence of muon beam and gamma background radiation. Encouraging results were obtained showing that the addition of CO2 to the standard gas mixture can represent a mid-term solution to reduce emissions and lower operational costs by keeping stable detector performance and safe long-term operation

Studies on RPC detectors operated with environmentally friendly gas mixtures in LHC-like conditions

Resistive Plate Chambers (RPC) are gasesous detectors employed at CERN LHC experiments thanks to their trigger performance, timing capabilities and contained production costs. High Pressure Laminate RPCs are operated with a three-component gas mixture, made of 90–95% of C$_2$H$_2$F$_4$, around 5% of i-C$_4$H$_{10}$ and 0.3% of SF$_6$. Due to the presence of leaks at detector level and to the greenhouse characteristics of C$_2$H$_2$F$_4$ and SF$_6$, RPCs in ATLAS and CMS were accounting for about 87% of CO$_2$ equivalent emissions during LHC Run 2. To address this, several alternative gases were studied, including R-1234ze as a possible substitute for R-134a. Furthermore, the addition of some amount of CO$_2$ into the RPCs gas mixture was explored as a possible short-to-medium term solution to lower the total greenhouse gas emissions and reduce the usage of C$_2$H$_2$F$_4$. A dedicated data taking campaign was performed at the Gamma Irradiation Facility at CERN, where RPCs detectors performance were studied with muon beam and gamma background. The detectors were operated with the addition of 30% and 40% and 50% of CO$_2$ to the standard gas mixture, together with an increased fraction of SF$_6$. Two different amounts of i-C4H10 were also evaluated to assess compatibility with the CMS and ATLAS requirements. Results from these beam tests with the above-mentioned gas mixtures are reported in this work

Studies on RPC detectors operated with environmentally friendly gas mixtures in LHC-like conditions

Resistive Plate Chambers (RPC) are largely employed at CERN LHC experiments thanks to their excellent trigger and timing performances. High Pressure Laminates (HPL) RPCs are operated with a gas mixture made of about 95% of C2H2F4, 5% of i-C4H10 and 0.3% of SF6. Both C2H2F4 and SF6 are known to be Greenhouse Gases (GHG), with a global warming potential of 1430 and 22800 respectively. Due to leaks at the detector level, RPCs accounted for about 87% of total GHG emissions from particle detectors at CERN during LHC Run 2. CERN has elaborated several strategies to reduce its GHG emissions and align with the European regulation on fluorinated gases. One strategy consists in the study of alternatives gases for particle detectors, with a particular focus on alternatives to R-134a and SF6. An experimental setup was designed to study RPC performances with eco-friendly gas mixture first with cosmic muons, where several gas mixtures could be tested. Few gas mixtures were then selected and a dedicated setup was installed at the Gamma Irradiation Facility of CERN to characterize detector performance with LHC-like background radiation and muon beam. Results with RPCs operated with lower GWP gas mixtures are presented in this work