Resistive Plate Chambers System Research Articles

Improved resistive plate chambers for HL-LHC upgrade of CMS

In view of the High Luminosity LHC, the CMS Muon system will be upgraded to sustain its efficient muon triggering and reconstruction performance. Resistive Plate Chambers (RPC) are dedicated detectors for muon triggering due to their excellent timing resolution. The RPC system will be extended up to 2.4 in pseudorapidity. Before the LHC Long Shutdown 3, new RE3/1 and RE4/1 stations of the forward Muon system will be equipped with improved Resistive Plate Chambers (iRPC) having, compared to the present RPC system, a different design and geometry and 2D strip readout. This advanced iRPC geometry configuration allows the rate capability to improve and hence survive the harsh background conditions during the HL-LHC phase. Several iRPC demonstrator chambers were installed in CMS during the recently completed 2nd Long Shutdown to study the detector behaviour under real LHC conditions. This paper summarizes the iRPC project and its schedule, including the status of the iRPC production sites, details of the chamber quality control procedures and results of the commissioning of the demonstrator chambers.

The ATLAS RPC system for the LHC Run-3

Resistive Plate Chambers (RPCs) provide the barrel region of the ATLAS detector with an independent muon trigger and a two-coordinate measurement. The chambers, 3720 gas volumes in total covering a surface area of 3650 m2, are arranged in three concentric double layers and operated in a strong magnetic toroidal field.The system was originally designed to operate for 10 years with an instantaneous luminosity up to the LHC nominal value of 1034 cm−2 s−1. After a successful data taking period in Run-2, when the instantaneous luminosity more than doubled its design value, the detector has undergone an intense maintenance to ensure an efficient data taking during the just started Run-3.Several interventions have been carried out on the detector mainly concerning the gas distribution with the aim of stabilizing the system and reducing the amount of gas released into the atmosphere. The main interventions were: (a) new gas distribution racks have been added in order to increase the vertical segmentation and in view of the installation of the new chambers for the phase-2 upgrade, (b) non-return valves have been installed on the chamber outputs to avoid reverse flow with large leaks, (c) a massive repair campaign has been done for fixing the continuously developing leaks, (d) a new repair technique to fix and prevent new leaks has been tested and (e) the segmentation of the HV channels has been doubled in a third of the spectrometer to mitigate the effect of detector failures.The different aspects of the activity carried out in LS2 (Long Shutdown 2) are described, from motivation to implementation. The first measurements to assess the system performance are also presented.

Latest results of Longevity studies on the present CMS RPC system for HL-LHC phase

The present Compact Muon Solenoid Resistive Plate Chambers system has been worked efficiently during Run I and Run II of data taking period (Shah et al., 2020) [1]. In the coming years of operation with the High Luminosity LHC (HL-LHC), the expected rate and integrated charge are expected to be about 600 Hz/cm2 and 840 mC/cm2, respectively (including a safety factor of three). Therefore, the HL-LHC phase will be a challenge for the RPC system since the expected operating conditions are much harsher than those for which the detectors have been designed, and could introduce non-recoverable aging effects which can alter the detector properties. A longevity test has been started at the CERN Gamma Irradiation Facility to estimate the impact of HL-LHC conditions on the RPC detector performance in order to determine whether the RPC system will survive the harsher background conditions expected at HL-LHC. The latest results of the irradiation test will be presented.

Machine Learning based tool for CMS RPC currents quality monitoring

The muon system of the CERN Compact Muon Solenoid (CMS) experiment includes more than a thousand Resistive Plate Chambers (RPC). They are gaseous detectors operated in the hostile environment of the CMS underground cavern on the Large Hadron Collider where pp luminosities of up to 2×1034cm−2s−1 are routinely achieved. The CMS RPC system performance is constantly monitored and the detector is regularly maintained to ensure stable operation. The main monitorable characteristics are dark current, efficiency for muon detection, noise rate etc. Herein we describe an automated tool for CMS RPC current monitoring which uses Machine Learning techniques. We further elaborate on the dedicated generalized linear model proposed already and add autoencoder models for self-consistent predictions as well as hybrid models to allow for RPC current predictions in a distant future.

New slow control emulator for the CMS phase-2 upgrade RPC link system

The CERN Compact Muon Solenoid (CMS) RPC system phase-2 upgrade project is in good progress. It covers the replacement of the off-detector electronics for the present Resistive Plate Chambers (RPC), known as “link system”, and includes the renovation of the legacy slow controller with brand new electronics, called RPC backend electronics. The scope of the new backend is to handle all requirements of the new RPC link system such as assigning a dedicated link to every control board (CB) that carries out the slow control and fast trigger commands and Large Hadron Collider (LHC) clock. In this work, we will review the architecture of the new Slow controller, its firmware, and the commands supported by this system.

Advances towards a large-area, ultra-low-gas-consumption RPC detector

Large Resistive Plate Chamber systems have their roots in High Energy Physics experiments at the European Organization for Nuclear Research: ATLAS, CMS and ALICE, where hundreds of square meters of both trigger and timing RPCs have been deployed. These devices operate with complex gas systems, equipped with re-circulation and purification units, which require a fresh gas supply of the order of 6 cm3/min/m2, creating logistical, technical and financial problems.In this communication, we present a new concept in the construction of RPCs which allowed us to operate a detector at ultra-low gas flow regime. With this new approach, the glass stack is encapsulated in a tight plastic box made of polypropylene, which presents excellent water vapor blocking properties as well as a good protection against atmospheric gases.

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.

Gas mixture quality studies for the CMS RPC detectors during LHC Run 2

Resistive Plate Chamber (RPC) detectors are widely employed in the muon trigger systems of three experiments at the CERN Large Hadron Collider (LHC). They are operated with gas mixture recirculation systems to reduce operational costs and greenhouse gas emissions since their gas mixture is based on C2H2F4, which has a high global warning potential. It is well known that the C2H2F4 molecule can break down under the effect of radiation and electric field. This leads to the creation of several impurities and free fluoride ions (F-), which could accumulate under gas recirculation and potentially attach to the RPC bakelite electrode inner surface. For these reasons, an extensive gas analysis campaign has been performed during LHC Run 2 for the CMS RPC system to verify gas mixture quality and possible accumulation of impurities.During the entire LHC Run 2 period, a gas chromatograph has been used to analyze the RPC gas mixture at different points of the gas system: quality of pure C2H2F4, fresh gas from the mixer, gas at the output of the detectors, and after the purifier module. Several impurities have been found and identified. Few impurities are already present in the C2H2F4 supply, as residuals of the industrial production. Nevertheless, it was found that some of these impurities, as well as others, are created inside the detector gas gap due to the fragmentation of the C2H2F4 molecule under the effects of electric field and radiation.During the 2018 LHC Run several gas analysis points were added to measure the fluoride ions production in different sectors of the RPC detector system. Indeed the products of the C2H2F4 fragmentation do not always recombine and F- species can stay free in the gas mixture. F- analyses were performed on the gas at the output of the detectors both for barrel and endcap regions, where radiation levels and operational conditions were different. In this way, it was possible to correlate the F- production with integrated charge, and gas mixture flow rate. In parallel, the RPC currents have been constantly monitored to look for possible correlations.Fluoride measurements have also been performed at GIF++ to better understand the correlation between F- production, radiation levels and gas volume exchanges.A comprehensive overview of the results obtained from the different types of gas analyses and possible correlation with RPC currents and LHC luminosity will be presented.

Aging study on Resistive Plate Chambers of the CMS Muon Detector for HL-LHC

In the High Luminosity Large Hadron Collider (HL-LHC) program, during the next years, the instantaneous luminosity will increase up to 5 × 1034 cm−2 s−1 which means a factor five higher than the nominal LHC luminosity. In that period, the present CMS Resistive Plate Chambers (RPC) system will be subjected to background rates higher than those for which the detectors have been designed, which could affect the detector properties and induce aging effects. To study whether the present RPC system can sustain the hard background conditions during the HL-LHC running period, a dedicated longevity test is ongoing at the CERN Gamma Irradiation Facility, where a few spare RPCs are exposed to high gamma radiation for a long term period to mimic the HL-LHC operational conditions. During the longevity test, the main detector parameters are continuously monitored as a function of the integrated charge. Preliminary results of the study, after having collected a sufficient amount of the expected integrated charge at HL-LHC, will be presented.

Improved-RPC for the CMS muon system upgrade for the HL-LHC

During Phase-2 of the LHC, known as the High Luminosity LHC (HL-LHC), the accelerator will increase its instantaneous luminosity to 5 × 1034 cm−2 s−1, delivering an integrated luminosity of 3000 fb−1 over 10 years of operation starting from 2027. In view of the HL-LHC, the CMS muon system will be upgraded to sustain efficient muon triggering and reconstruction performance. Resistive Plate Chambers (RPCs) serve as dedicated detectors for muon triggering due to their excellent timing resolution, and will extend the acceptance up to pseudorapidity values of |η|=2.4. Before Long Shutdown 3 (LS3), the RE3/1 and RE4/1 stations of the endcap will be equipped with new improved Resistive Plate Chambers (iRPCs) having different design and geometry than the present RPC system. The iRPC geometry configuration improves the detector's rate capability and its ability to survive the harsh background conditions of the HL-LHC . Also, new electronics with excellent timing performances (time resolution of less than 150 ps) are developed to read out the RPC detectors from both sides of the strips to allow for good spatial resolution along them. The performance of the iRPC has been studied with gamma radiation at the Gamma Irradiation Facility (GIF++) at CERN. Ongoing longevity studies will help to certify the iRPCs for the HL-LHC running period. The main detector parameters such as the current, rate and resistivity are regularly monitored as a function of the integrated charge. Preliminary results of the detector performance will be presented.

RPC system in the CMS Level-1 Muon Trigger

The CMS experiment implements a two-level triggering system composed of Level-1, instrumented by custom-design hardware boards, and a software High Level Trigger. To cope with the more challenging luminosity conditions, a new Level-1 architecture has been deployed during run II. This new architecture exploits in a better way the redundancy and complementarity of the three muon subsystems: Cathode Strip Chambers (CSC), Drift Tubes (DT) and Resistive Plate Chambers (RPC). The role of each subsystem in the Level-1 Muon Trigger is described here, highlighting the contribution from the RPC system. Challenges brought by the HL-LHC environment and new possibilities coming from detector and trigger upgrades are also discussed.

Outgassing and leak test of INO-ICAL RPC detectors

Glass Resistive Plate Chambers (RPCs) of size 2 m × 2 m, operated in avalanche mode will be used as an active detector element at the INO-ICAL experiment. The RPC system of the ICAL experiment will operate with a gas mixture of C2H2F4 (94.5%), isobutane (5%) and SF6 (0.5%). To fulfil the physics goals, about 29,000 RPCs will be used which are expected to last for 20 years or more. The quality and purity of the gas plays a vital role in the stable operation of RPC detectors. The presence of impurities in a gas mixture contribute towards the degradation of detector performance. The various assembly materials like glues, button spacers, frames, etc. used in the construction of the chamber may outgas and contaminate the gas mixture. We have performed the very first study to estimate the outgassing due to various materials used in the construction of INO RPCs. The present study includes the results obtained from gas chromatography showing the generation of impurities and dangerous radicals produced due to outgassing when RPC are operated in the cosmic stand. The study also includes a test of purity and effectiveness of the gas mixing system. Since a large amount of gas mixture is to be circulated inside the RPC during the operation of the ICAL detector, a proper leak test will help to minimize gas leaks reducing operational costs and atmospheric air pollution. A proper quantitative leak test is also performed on RPC after assembly by monitoring the absolute pressure inside the chamber, along with the atmospheric pressure and temperature to estimate the leakage rate.

Studies of the gas volume current density in the ATLAS Resistive Plate Chamber detector during the 2018 data-taking at the LHC

The ATLAS Resistive Plate Chamber (RPC) detector is a tracking detector, used to primarily trigger muons in the ATLAS barrel region (which corresponds to a pseudorapidity range of |η|<1.05) at the 40 MHz collision rate, and to provide η and ϕ coordinates. The RPC system consists of about 3700 gas volumes covering a sensitive surface of about 4000 m2. It is arranged in three concentric doublet layers at radius 7 m, 8 m and 10 m, and operating in an approximately 0.5–1 T toroidal magnetic field. RPCs provide up to 6 space points along the muon track with a space-time resolution of about 1 cm2 × 1 ns. This document studies systematically the gas volume current as a function of the electric field applied across the gas volume and of temperature both with and without the Large Hadron Collider (LHC) beam induced background and up to an instantaneous luminosity Linst = 2×1034 cm−2 s−1 (twice larger than the design LHC luminosity). These measurements have been used to study the RPC working conditions and to extrapolate the detector response to the High-Luminosity LHC regime with Linst = 7.5×1034 cm−2 s−1.

CMS RPC activities during LHC LS-2

The second LHC long shutdown period (LS2) is an important opportunity for the CMS Resistive Plate Chambers (RPC) to complete their consolidation and upgrade projects. The consolidation includes detector maintenance for gas tightness, HV (high voltage), LV (low voltage) and slow control operation. All services for the RPC Phase-2 upgrade: improved RPC in stations RE3/1 and RE4/1, were anticipated for installation to LS2. This paper summarises the RPC system maintenance and upgrade activities.

Status of the present ATLAS RPC system and overview towards HL-LHC

The Resistive Plate Chamber (RPC) system covers the barrel region of the ATLAS muon spectrometer [1] in the pseudo-rapidity range |η|<1.05, with six independent detector layers exclusively providing the first level trigger signal and the track coordinate in the non-bending plane of the muon candidates. The system is designed to operate up to the nominal Large Hadron Collider luminosity ( ℒ = 1034 cm−2 s−1) which has been already exceeded thanks to the excellent performance of the collider. The experience in operating the present RPC system, up to the maximum instantaneous luminosity of 2.06 × 10 34 cm−2 s−1 reached in 2017, is reported. The performance of the system, in the severe background and pileup conditions of the last data taking period, is presented together with the improved tools implemented in order to have an effective monitoring of the detector status. The plans to successfully operate the present system during the HL-LHC phase are also introduced.

Gas mixture quality monitoring for the RPC detectors at the LHC experiments

Resistive Plate Chamber (RPC) detectors are widely employed in the muon trigger systems of three experiments at the CERN Large Hadron Collider (LHC) thanks to their excellent time resolution. The LHC RPC systems are operated under gas recirculation to reduce operation cost and greenhouse gas emissions since their gas mixture is based on C2H2F4, which has a global warning potential of 1430 and it is subject to the European F-gas Regulation. Extensive gas analysis campaigns have been performed during LHC Run 2 for the CMS RPC and ALICE Muon Trigger (MTR) systems to verify the gas mixture quality and possible accumulation of impurities. A particular attention has been addressed to the ALICE MTR system, which has been operated under gas recirculation from the end of 2015. In order to validate the system ensuring good detector operation, the gas recirculation has been increased in steps: 30%, 60% and 70%. Detector currents and gas mixture quality have been closely monitored. A gas chromatograph and mass spectrometer (GC/MS) station has been installed to analyze the MTR gas mixture in different points of the gas system: fresh gas from the mixer, detectors output and output of the purifier module. Several impurities have been found and identified. Most of the impurities are created inside the detector gas gap due to the fragmentation of the C2H2F4 molecule under the effects of electric field and radiation. The GC/MS analyses have been regularly performed in 2016 and 2017. It has been demonstrated that impurities concentration (at the level of tens of ppm) increases with the increase of the gas recirculation fraction. GC/MS analyses have been also performed after the purifier module showing that some impurities are filtered while others not. In parallel, the RPC currents have been constantly monitored, and their trend showed no correlation with the gas recirculation fraction. In 2017 an Ion Selective Electrode station was installed to measure the fluoride ions (F−) concentration in the MTR RPC gas mixture. Indeed the products of the C2H2F4 fragmentation not always recombine and F^− species can stay free in the gas mixture. The analyses show that F− are present in the mixture exiting the RPCs and their concentration increases with the increase of luminosity, even if it stays at the level of ppb per day. A comprehensive overview of the results obtained from the different types of gas analyses and possible correlation with RPC currents and LHC luminosity will be presented.

Gas recirculation and recuperation systems for Resistive Plate Chamber operation with new environmental friendly gases

Resistive Plate Chamber (RPC) detectors are widely used thanks to their excellent time resolution and low production cost. The large RPC systems at the CERN-LHC experiments are operated in avalanche mode thanks to a R134a-based gas mixture with the addition SF6 and iC4H10 in low concentrations (0.3% and 5% respectively). However, due to their high global warming potential (GWP), R134a has been phased out from production and SF6 will be probably phased out very soon. Although R134a and SF6 will always be technically available for research purposes, their cost will probably increase as the interest of industry and market will gradually move towards new eco-friendly refrigerants and insulators. In addition, the reduction of R134a and SF6 emission in the atmosphere from anthropogenic activityis is of paramount importance because GHGs are believed to be at the origin of climate changes. Several gas mixtures based on new environmental friendly gases have been tested in the past few years. Results obtained with new gas mixtures based on hydro-fluoro-olephin (R1234ze), CO2 and C4F8O are presented. A parallel strategy for reducing the GHG emission is focused on the development of new gas recirculation and recuperation systems. The present contribution describes the last results obtained during the first test of RPC detectors operated with new environmental friendly gas mixture and new gas recirculation system. Other strategies for GHG emission reduction will be discussed as a part of a wider R&D program.

Streamer studies in Resistive Plate Chambers

The present paper is meant as an update of the presentation given in a previous Resistive Plate Chamber (RPC) workshop, aimed at finding an eco-friendly gas mixture for streamer operation of RPCs. Indeed the streamer working regime is still suitable for building large RPC systems dedicated to low rate applications, such as cosmic ray and neutrino physics. In addition to other studies about gas mixtures for streamer mode operation, in this paper the replacement of R134a with CF4, a gas widely used in other gaseous detectors, has been investigated. The effect of the gas gap thickness on the discharge quenching has also been studied; this is an important check because thin gas gaps of 1 mm, one half of the typical used value, have been introduced for high rate applications. Finally preliminar results about the streamer formation timing are also reported.

Operation and performance of the CMS Resistive Plate Chambers during LHC run II

The Resistive Plate Chambers (RPC) at the Compact Muon Solenoid (CMS) experiment at the CERN Large Hadron Collider (LHC) provide redundancy to the Drift Tubes in the barrel and Cathode Strip Chambers in the endcap regions. Consisting of 1056 double gap RPC chambers, the main detector parameters and environmental conditions are carefully monitored during the data taking period. At a center of mass energy of 13 TeV, the luminosity reached record levels which were challenging from the operational and performance point of view. In this work, the main operational parameters are discussed and the overall performance of the RPC system is reported for the LHC run II data taking period. With a low amount of inactive chambers, a good and stable detector performance was achieved with high efficiency.

First results of CMS RPC performance at 13 TeV

The muon spectrometer of the CMS (Compact Muon Solenoid) experiment at the Large Hadron Collider (LHC) is equipped with a redundant system made of Resistive Plate Chambers (RPCs) and Drift Tube (DT) chambers in the barrel, RPC and Cathode Strip Chambers (CSCs) in the endcap region. In this paper, the first results of the performance of the RPC system during 2015 with the LHC running at 13 TeV is presented. The stability of the RPC performance, in terms of efficiency, cluster size and noise, is reported.