Resistive Plate Chamber Detectors Research Articles

Fine tuning of gas system and performance studies of RPC detectors in the INO's mini-ICAL detector

The India-based Neutrino Observatory's (INO) Iron CALorimeter (ICAL) experiment will be instrumented with about 28,800 large area glass Resistive Plate Chambers (RPCs) as active detector elements. The mini-ICAL, which is a 600-times scaled-down prototype version of the ICAL, is currently in operation at the Inter Institutional Centre for High Energy Physics (IICHEP), a transit campus of the INO project in Madurai, India. The 4 m×4 m detector comprises an ∼ 85 t magnet, built using 11 layers of iron plates to accommodate 10 layers of RPCs — two RPCs per layer. A closed-loop gas system (CLS) is designed to supply gas mixture of R134a (95.2%), isobutane (4.5%), and SF 6 (0.3%) to the mini-ICAL, collect the return gas from the RPCs, purify it using filters, and recirculate the mixture into the detector. Contamination of any kind into the gas mixture will severely affect the characteristics of the RPC detectors, such as the dark current and noise rates, and consequently deteriorate performance of the RPC detector. The contamination is mainly caused due to leaks within the gas system, in the gas lines and in the RPC gas gap volume. This paper deals with systematic identification and mitigation of leaks within the closed-loop gas system and performance improvement of the RPCs installed in the mini-ICAL detector.

The RPC in the astroparticle physics of the next future

Following the brilliant results of the ARGO-YBJ experiment (Tibet, 4300 m asl), this paper intends to investigate how to optimize the potential of Resistive Plate Chambers (RPCs) for detecting cosmic-ray showers. This requires improving parameters like construction simplicity, low cost, and working reliability in hostile environments, rather than high-rate capability and time resolution as required in collider experiments. RPCs are particularly suitable for the detection of very low energy showers, as shown by ARGO-YBJ. An example of RPC detector, conceived for cosmic-ray physics and gamma-ray astronomy, particularly Gamma Ray Burst (GRB) observation, will be shown. This is of great interest in view of a large-size cosmic-shower detector to be installed in the Southern hemisphere.

Studies of C2H2F4 and SF6 alternative gas mixtures for HPL RPC detectors for High Energy Physics applications

This research investigates the viability of replacing greenhouse gases C2H2F4 and SF6 with eco-friendly gas mixtures in Resistive Plate Chamber (RPC) detectors used at CERN LHC experiments. The study focuses on the addition of CO2 as a substitute of C2H2F4 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 SF6, including 3M NOVECTM 4710 and AMOLEATM 1224yd, presenting perforances results about these gas alternatives in High Pressure Laminate RPCs.

On a new environment-friendly gas mixture for Resistive Plate Chambers

The standard gas mixture for the Resistive Plate Chambers (RPC), composed of C2H2F4/i-C4H10/SF6, allows the detector operation in avalanche mode, as required by the high-luminosity collider experiments. The gas density, the low total charge delivered inside the gas and the comfortable avalanche-streamer separation guarantee high detection efficiency, rate capability and slow detector aging. The standard RPC gas mixture is mostly based on Hydrofluorocarbons, HFCs, extensively used in the refrigeration industry. The Hydrofluorocarbons are now considered to be non-eco-friendly gases for their high Global Warming Potential (GWP). The SF6 has the largest GWP, 22900, but, due to its low concentration, it contributes only with few tens of units to the total value. The major contribution comes from the main standard gas mixture component, the C2H2F4 (GWP ≈ 1300). These gases are not recommended for industrial uses anymore, thus their availability will be increasingly difficult over time and the search for an alternative gas mixture with low-GWP is then of absolute priority within the RPC community. We report the performance of the RPC working with new environment-friendly gases which could replace the standard mixture. In this work the standard mixture main component, the C2H2F4, is replaced by a proper mixture of CO2 (GWP = 1) and Tetrafluoropropene (C3H2F4, GWP≈6). The other high-GWP component, the SF6, is replaced by a molecule, the Chloro-Trifluoropropene (C3H2ClF3, GWP ≈ 5) never tested in RPC detectors. The mixtures studied have a total GWP ≈ 10. We report, for several eco-gas mixtures, the detection efficiency, streamer probability, electronic and ionic charge as a function of the high voltage. Moreover, the timing properties are studied and the detector time resolution is measured. We also focus the attention on a new category of signals having intermediate properties between avalanche and streamer, called ”transition events”. This category is negligible for the standard gas mixture but relevant for HFO/CO2-based gas mixtures. We show a direct comparison between SF6 and C3H2ClF3 to study in depth the possibility to replace the SF6.

Comparative study of electron beam and gamma ray irradiation effects in RPC glass detector materials by positron lifetime spectroscopy

This work is intended to compare the electron beam and gamma ray irradiation induced microstructural effects and electrical conductivity in glass Resistive Plate Chamber (RPC) detector materials with different doses. Positron annihilation lifetime spectroscopic (PALS) technique was used to analyze the irradiation induced structural modifications in the RPC detector materials. PALS analysis at lower doses indicates the increased void size with the creation of additional sites in the glass network upon both the irradiation sources. At higher irradiation doses, the reduced void size shows the enhanced chemical bonding between the tetrahedral sites of Si-O-Si and hence increases the short range order in the silica glass. The variation of DC conductivity upon both the irradiation techniques correlates well with the measured void size. Gamma ray irradiation produced more structural changes in the glass samples as compared to the electron beam irradiation.

Eco-friendly Resistive Plate Chambers for detectors in future HEP applications

Resistive Plate Chamber detectors are largely used in current High Energy Physics experiments, typically operated in avalanche mode with large fractions of Tetrafluoroethane (C2H2F4), a gas recently banned by the European Union due to its high Global Warming Potential (GWP). An intense R&D activity is ongoing to improve RPC technology in view of future HEP applications. In the last few years the RPC EcoGas@GIF++ Collaboration has been putting in place a joint effort between the ALICE, ATLAS, CMS, LHCb/SHiP and EP-DT Communities to investigate the performance of present and future RPC generations with eco-friendly gas mixtures. Detectors with different layout and electronics have been operated with ecological gas mixtures, with and without irradiation at the CERN Gamma Irradiation Facility (GIF++). Results of these performance studies together with plans for an aging test campaign are discussed in this article.

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_2H_2F_4, around 5% of i-C_4H_{10} and 0.3% of SF_6. Due to the presence of leaks at detector level and to the greenhouse characteristics of C_2H_2F_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_2H_2F_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.

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.

Aging studies for the CMS improved Resistive Plate Chambers

For the High Luminosity (HL-LHC) upgrade an upgrade of the CMS detector is foreseen. One of the main projects is the development of the improved Resistive Plate Chamber (iRPC) detectors that will be installed in the forward region of CMS. To validate the performance of the new detector gaps with HL-LHC radiation levels, experimental tests have been conducted at the CERN Gamma Irradiation Facility (GIF++). One chamber equipped with electronics is studied and its parameters are monitored as a function of the accumulated charge.

GEM detectors for the CMS endcap muon system: status of three new detector stations

The High-Luminosity LHC (HL-LHC, or Phase-2 LHC) will deliver proton-proton collisions at 5–7.5 times the nominal LHC luminosity, with an expected number of 140–200 pp-interactions per bunch crossing (Pile-up or PU). To maintain the performance of muon triggering and reconstruction under high background, the forward part of the Muon Spectrometer of the CMS experiment will be upgraded with Gas Electron Multipliers (GEM) and improved Resistive Plate Chambers (iRPC) detectors [1,2]. A first GEM station (GE1/1) was installed during Long Shutdown 2 (LS2, 2019–2021), a 2nd station (GE2/1) of Triple-GEM detectors will be installed in winter 2023–24 and 2024–25, while a new 6-layer station (ME0) will be installed in the third Long Shutdown (LS3, 2026–2028). GE11 is considered an early Phase-2 upgrade as it will reduce the pT threshold by combining GEM and Cathode Strip Chamber (CSC) hits in the forward muon system at twice the LHC design luminosity (ℒ = 2 · 1034 cm-2 s-1, 50 PU). After a successful start of Run-3 in 2022, with almost 40 fb-1 collected, the commissioning of the GE1/1 detector is nearly complete. Most chambers are operated stably with an efficiency in excess of 95%, next being the demonstration of the combined CSC-GEM trigger in 2023. The lessons learnt with the first large-area GEM station have lead to improvements in detector and electronics design for the Phase 2 detectors GE2/1 and ME0. This proceeding will discuss the progress made since last MPGD Conference (MPGD 2019) [3], discussing the commissioning and early performance of GE1/1; the design improvements and start of construction of GE2/1; and the R&D currently ongoing for ME0.

Measurements of fluoride production in Resistive Plate Chambers

Resistive Plate Chambers (RPCs) are operated with a gas mixture made of C2H2F4, SF6 and iC4H10. 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, C2H2F4 and He or CO2 were used to study the RPC F− production in presence of the HFO1234ze, which is less stable in atmosphere with respect to the C2H2F4.

Description and stability of a RPC-based calorimeter in electromagnetic and hadronic shower environments

The CALICE Semi-Digital Hadron Calorimeter technological prototype completed in 2011 is a sampling calorimeter using Glass Resistive Plate Chamber (GRPC) detectors as the active medium. This technology is one of the two options proposed for the hadron calorimeter of the International Large Detector for the International Linear Collider. The prototype was exposed in 2015 to beams of muons, electrons, and pions of different energies at the CERN Super Proton Synchrotron. The use of this technology for future experiments requires a reliable simulation of its response that can predict its performance. GEANT4 combined with a digitization algorithm was used to simulate the prototype. It describes the full path of the signal: showering, gas avalanches, charge induction, and hit triggering. The simulation was tuned using muon tracks and electromagnetic showers for accounting for detector inhomogeneity and tested on hadronic showers collected in the test beam. This publication describes developments of the digitization algorithm. It is used to predict the stability of the detector performance against various changes in the data-taking conditions, including temperature, pressure, magnetic field, GRPC width variations, and gas mixture variations. These predictions are confronted with test beam data and provide an attempt to explain the detector properties. The data-taking conditions such as temperature and potential detector inhomogeneities affect energy density measurements but have small impact on detector efficiency.

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.

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.

Performance studies of RPC detectors operated with C2H2F4 and CO2 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.

Test and characterisation of STS/MuCh-XYTER and integration with multiple detectors of CBM-MuCh detector systems

Compressed Baryonic Matter (CBM) is a fixed target experiment at the upcoming Facility for Anti-proton and Ion Research in Germany, having collision rates up to 10 MHz. Due to the proximity of the target and secondaries produced in absorbers, Muon Chambers (MuCh) of the CBM experiment will face a very high particle hit rate of up to 400 kHz/cm2 in its first two stations. To cope with these particle rates, a Gas Electron Multiplier (GEM) detector will be used for the first two stations while, due to relatively lower particle rates, the last two stations will use a low resistivity Bakelite Resistive Plate Chamber (RPC) detector. The electronics of these two MuCh detectors need different dynamic ranges.A Silicon Tracking Station (STS) system made of 300 μm thick silicon micro-strip sensors will be installed upstream of the MuCh detector system. The sensors will be read out through multi-line micro-cables with fast electronics. The micro-strip sensors will be double-sided with a stereo angle of 7.5°, a strip width of 58 μm, and strip lengths between 20 and 120 mm requiring high-density readout.To meet the high rate and high density requirements of MuCh and STS, respectively, a specialized 128-channel readout ASIC with a dual-gain feature is designed. This is a highly configurable ASIC with about 30,000 configurable register bits which control various bias and threshold settings of the ASIC. To integrate this ASIC with both the detector systems, detailed testing and characterization of the ASIC are required.Due to the high number of configurable registers and several operating conditions, characterizing this ASIC is very challenging. This paper describes the optimization procedures of several configurable bias parameters in detail and also explains how this ASIC is integrated with both GEM and RPC detectors of the MuCh system.

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.

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. CF4 is used for wire chambers and Gas Electron Multiplier (GEM) detectors while C2H2F4 and SF6 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.

Performance and Integration Results of a High Resolution Time-to-Digital Converter Designed for INO ICAL Experiment

INO ICAL Experiment emphasis on studying various properties of atmospheric neutrinos. A 50 kton Iron Calorimeter and Resistive plate Chamber (RPC) in stacked geometry will be used to track neutrinos. Position and directional information are to be used to identify particle energies. RPC detector signal of rise time less than 1ns is amplified-discriminated and given to Digital Front End (RPC-DAQ). To measure these fast pulses, we designed a low power, compact multi-channel Delay Chain based time-to-digital converter (TDC) in a 0.13μm CMOS process which will be integrated with the RPC-DAQ module. This TDC is capable of handling multiple hits per channel with a single-shot precision better than 65.34 ps. A 4-line or 11-line serial peripheral interface (SPI) is used for readout and configuration. This paper presents the performance and integration results of this TDC.

Longevity study on the CMS resistive plate chambers for HL-LHC

The CMS Resistive Plate Chamber (RPC) system has been certified for 10 years of LHC operation. In the next years, during the High luminosity LHC (HL-LHC) phase, the LHC instantaneous luminosity will increase to a factor five more than the existing LHC luminosity. This will subject the present CMS RPC system to background rates and operating conditions much higher with respect to those for which the detectors have been designed. Those conditions could affect the detector properties and introduce nonrecoverable aging effects. A dedicated longevity test is set up in the CERN Gamma Irradiation Facility (GIF++) to determine if the present RPC detectors can survive the hard background conditions during the HL-LHC running period. During the irradiation test, the RPC detectors are exposed to a high gamma radiation for a long period and the detector main parameters are monitored as a function of the integrated charge. Based on collecting a large fraction of the expected integrated charge at the LH-LHC. The results of the irradiation test will be presented.