Glass Resistive Plate Chambers 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.

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.

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.

Muon detector for a Muon Collider

A Muon Collider represents a promising possibility to combine the high energy and luminosity of hadron machines with very precise measurements of lepton colliders. The main challenges, that impact both the machine and detector design, arise from the short muon lifetime and the harsh Beam-induced Background (BIB).Therefore, a full simulation is crucial to understand the feasibility of the experiment implementation. Focusing in particular on the muon system, a preliminary simulation of sensitivity and hit rate reveals that the technology inherited from CLIC, i.e. glass Resistive Plate Chambers, is already at the limit of its rate capability. Thus, alternative MicroPattern Gaseous Detector solutions are under investigation to try to match the required performance. In parallel, studies of muon reconstruction are ongoing.Results of the muon reconstruction efficiency and BIB sensitivity are presented for multimuon final state processes at a centre-of-mass energy of 1.5TeV. Besides, PICOSEC technology, based on a Micromegas detector coupled to a Cherenkov radiator and equipped with a photocathode, is discussed.

Development of Novel Designs of Resistive Plate Chambers

A novel design of Resistive Plate Chambers (RPCs), using only a single resistive plate, was developed and tested. Based on this design, prototype chambers of size ranging from 10 cm × 10 cm to 32 cm × 48 cm were constructed and tested with cosmic rays and particle beams. The tests confirmed the viability of this new approach for calorimetric applications where the particle rates do not exceed 1 kHz/cm2, such as CALICE digital calorimeters. The chambers also have improved single-particle response, such as a pad multiplicity close to unity. In addition to this development, we probed a new technique to mitigate limitations associated with common RPC gases compatible with the environment. The technique is based on electron multiplication in a thin layer of high secondary electron yield material coating on the anode plane. Here we report on the construction of various different glass RPC designs, and their performance measurements in laboratory tests and with particle beams.

Development of Novel Designs of Resistive Plate Chambers

Resistive Plate Chambers (RPCs) are a key active media of the muon systems of current and future collider experiments as well as the CALICE (semi-)digital hadron calorimeter. The outstanding issues with RPCs can be listed as the loss of efficiency for the detection of particles when subjected to high particle fluxes and the limitations associated with the common RPC gases. We developed novel RPC designs with: low resistivity glass plates; a single resistive plate; and a single resistive plate and a special anode plate coated with high secondary electron emission yield material. The cosmic and beam tests confirmed the viability of these new approaches for calorimetric applications. The chambers also have improved single-particle response, such as a pad multiplicity close to unity. Here, we report on the construction of various different glass RPC designs and their performance measurements in laboratory tests and with particle beams. We also discuss future test plans, which include the long-term performance tests of the newly developed RPCs, investigation of minimal gas flow chambers, and feasibility study for the large-size chambers.

Energy reconstruction of hadronic showers at the CERN PS and SPS using the Semi-Digital Hadronic Calorimeter

The CALICE Semi-Digital Hadronic CALorimeter (SDHCAL) is the first technological prototype in a family of high-granularity calorimeters developed by the CALICE Collaboration to equip the experiments of future lepton colliders. The SDHCAL is a sampling calorimeter using stainless steel for absorber and Glass Resistive Plate Chambers (GRPC) as a sensitive medium. The GRPC are read out by 1 cm× 1 cm pickup pads combined to a multi-electronics. The prototype was exposed to hadron beams in both the CERN PS and the SPS beamlines in 2015 allowing the test of the SDHCAL in a large energy range from 3 GeV to 80 GeV. After introducing the method used to select the hadrons of our data and reject the muon and electron contamination, we present the energy reconstruction approach that we apply to the data collected from both beamlines and we discuss the response linearity and the energy resolution of the SDHCAL. The results obtained in the two beamlines confirm the excellent SDHCAL performance observed with the data collected with the same prototype in the SPS beamline in 2012. They also show the stability of the SDHCAL in different beam conditions and different time periods.

Performance study of large-area glass resistive plate chambers with different spacer configurations

Optimization of spacer and gas distribution inside the glass resistive plate chamber (RPC) is reported. Simulation studies demonstrate improvements on the gas flow velocity homogeneity and lower vorticity inside the gas chamber. The optimized spacer configuration (76 spacers) decreases the number of spacers by 24% compared to the original design (100 spacers), thus helps significantly reduce the non-active or low-efficiency area caused by spacers while maintaining similar deformation uniformity of the electrodes. Large area glass RPCs with 1×1 m^2 size using two types of spacer configurations are constructed and tested with cosmic muons events. The muon detection efficiencies for RPCs are greater than 95%.

The gas flow pattern through small size Resistive Plate Chambers with 2 mm gap

A prototype of a single-gap glass Resistive Plate Chamber (RPC) is constructed by the authors. To find the requirements for better operation of the detector's gas system, we have simulated the flow of the Argon gas through the detector by using computational fluid dynamic methods. Simulations show that the pressure inside the chamber linearly depends on the gas flow rate and the chamber's output hose length. The simulation results were compatible with experiments. We have found that the pressure-driven speed of the gas molecules is two orders of magnitude larger in the inlet and outlet regions than the blocked corners of a 14 × 14 cm2 chamber, and most likely the difference in speed is higher for larger detectors and different geometries.

Study of particle multiplicity of cosmic ray events using 2 m × 2 m resistive plate chamber stack at IICHEP-Madurai

An experimental setup consisting of 12 layers of glass Resistive Plate Chambers (RPCs) of size 2\,m\,$\times$\,2\,m has been built at IICHEP-Madurai (\ang{9;56;14.5}\,N \ang{78;00;47.9}\,E, on the surface) to study the long term performance and stability of RPCs produced on large scale in Indian industry. This setup has been collecting data triggered by the passage of charged particles. The measurement of the multiplicity of charged particles due to cosmic ray interactions are presented here. Finally, the results are compared with different hadronic models of the CORSIKA simulation.

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.

Particle identification using Boosted Decision Trees in the Semi-Digital Hadronic Calorimeter prototype

The CALICE Semi-Digital Hadronic CALorimeter (SDHCAL) prototype using Glass Resistive Plate Chambers as a sensitive medium is the first technological prototype of a family of high-granularity calorimeters developed by the CALICE collaboration to equip the experiments of future leptonic colliders. It was exposed to beams of hadrons, electrons and muons several times in the CERN PS and SPS beamlines between 2012 and 2018. We present here a new method of particle identification within the SDHCAL using the Boosted Decision Trees (BDT) method applied to the data collected in 2015. The performance of the method is tested first with Geant4-based simulated events and then on the data collected by the SDHCAL in the energy range between 10 and 80 GeV with 10 GeV energy steps. The BDT method is then used to reject the electrons and muons that contaminate the SPS hadron beams. The rejection power of the new method is estimated to be as high as 99.0% for the muons and 99.4% for the electrons associated to a pion selection efficiency of about 95.0%.

Towards portable muography with small-area, gas-tight glass Resistive Plate Chambers

Imaging techniques that use atmospheric muons, collectively named under the neologism “muography”, have seen a tremendous growth in recent times, mainly due to their diverse range of applications. The most well-known ones include but are not limited to: volcanology, archaeology, civil engineering, nuclear reactor monitoring, nuclear waste characterization, underground mapping, etc. These methods are based on the attenuation or deviation of muons to image large and/or dense objects where conventional techniques cannot work or their use becomes challenging. In this context, we have constructed a muography telescope based on “mini glass-RPC” planes following a design similar to the glass-RPC detectors developed by the CALICE Collaboration and used by the TOMUVOL experiment in the context of volcano radiography, but with smaller active area (16× 16 cm2). The compact size makes it an attractive choice with respect to other detectors previously employed for imaging on similar scales. An important innovation in this design is that the detectors are sealed. This makes the detector more portable and solves the usual safety and logistic issues for gas detectors operated underground and/or inside small rooms. This paper provides an overview on our guiding principles, the detector development and our operational experiences. Drawing on the lessons learnt from the first prototype, we also discuss our future direction for an improved second prototype, focusing primarily on a recently adopted serigraphy technique for the resistive coating of the glass plates.

Effect of Ar+ Ion Implantation-Induced Microstructural Modifications on Electrical Conductivity of Glass RPC Detector Materials

Argon ions with energy of 1 MeV and 500 keV are implanted at various fluences into Asahi and Saint Gobain clear float glasses used for resistive plate chamber (RPC) detector fabrication. The decreased size of voids (Vf) in the selected glasses is interpreted as an increased short-range order of the glass structure at higher fluence of argon ion implantation. The increased local temperature influences the diffusion of argon ions via trapping in the silica glass voids for higher implantation fluence. The slight increase in bandgap energy (Eg) in the glass RPC detector materials at higher argon ion implantation fluence observed reduced electrical conductivity. The increased energy bandgap in the float glass RPC detector samples enhanced surface resistivity, consequently reducing the leakage current.

RPC performance with HARDROC based readout

The proposed 51 kton magnetized Iron Calorimeter (ICAL) detector at India based Neutrino Observatory (INO) aims to investigate atmospheric neutrino oscillations. ICAL will use approximately 29000 glass-based Resistive Plate Chambers (RPCs) as active detector elements, that require millions of electronic channels to be read. Therefore, a multi-channel readout Application Specific Integrated Circuit (ASIC) named as HARDROC can be considered as a possible option. The ASIC is a 64 channel analog-digital front-end chip that can read negative fast and short input signals. Each of the HARDROC channels features a current sensitive pre-amplifier coupled to the triple-branch shaper stage and then 3 low offset discriminators. A comparative performance study of the RPC detector with HARDROC ASIC and with custom electronics, based on CAEN modules and HMC pre-amplifiers, was conducted. Measurements were made on a 30cm × 30cm glass RPC detector using the cosmic rays. The purpose of this work was to compare detector performance in terms of their strip detective efficiency and count rate.

Measurement of azimuthal dependent muon flux by 2 m × 2 m RPC stack at IICHEP-Madurai

The proposed 50 \,kton\, INO-ICAL experiment is an upcoming underground high energy physics experiment planned to be commissioned at Bodi hills near Theni, India ($9^{\circ}57'N$, $77^{\circ}16'E$) to study various properties of neutrino oscillations using atmospheric neutrinos produced by extensive air shower phenomenon. The resistive plate chamber has been chosen as the active detector element for the proposed INO-ICAL. An experimental setup consisting a stack of 12 layers of glass resistive plate chambers each with a size of $\sim$2\,m$\times$2\,m has been built at IICHEP, Madurai to study the performance and long-term stability of the resistive plate chambers(RPCs) commercially produced in large quantities by the Indian industries as well as its electronics for the front-end and subsequent signal processing. In this study, the azimuthal dependence of muon flux at various zenith angles at Madurai (9$^{\circ}$56'N, 78$^{\circ}$00'E and at an altitude of 160\,m above mean sea level) has been presented along with the comparison of Monte Carlo from CORSIKA and HONDA predictions.

Particle identification using Boosted Decision Trees in the semi-digital hadronic calorimeter

The CALICE Semi-Digital Hadronic CALorimeter (SDHCAL) prototype using Glass Resistive Plate Chambers as a sensitive medium is the first technological prototype in a family of high-granularity calorimeters developed by the CALICE collaboration to equip the experiments of future leptonic colliders. It was exposed to beams of hadrons, electrons and muons several times on the CERN PS and SPS beamlines in 2012, 2015 and 2016. We present here a new method of particle identification within the SDHCAL using the Boosted Decision Tree (BDT) method applied to the data collected in 2015. The performance of the method is tested first with GEANT4-based simulated events and then on the data collected in the SDHCAL in the energy range between 10 and 80 GeV with 10 GeV energy steps. The BDT method is then used to reject the electrons and muons which contaminate the SPS hadron beams.

Effect of variations in the gas mixture compositions on the timing and charge of glass RPC

The India-based Neutrino Observatory (INO) is a project aimed at building a large underground laboratory to explore the Earth's mater effects on the atmospheric neutrinos in multi-GeV range. INO will host a 50 kton magnetized iron calorimeter detector (ICAL) in which Resistive Plate Chambers(RPCs) will be the active detector elements. In ICAL, 28,800 glass RPCs of 2 m × 2 m size will be operated in the avalanche mode. A small variation in the compositions of ionizing gaseous medium in the RPC affects its performance. Study of the charge distribution of the RPC at different gas compositions is necessary to optimize the gas mixture. An RPC made with glass plates of dimension 30 cm × 30 cm was operated in avalanche mode with a gas mixture of C2H2F4/iC4H10/SF6. We have studied the performance of these RPCs at the same ambient conditions. The percentages of the iC4H10 or SF6 were varied and its effect on the performance of RPC were studied. The study of the charge distribution and time resolution of the RPC signals at different gas compositions is presented in this paper.

Studies on thermally induced microstructural modifications and electrical conductivity in glass RPC detector materials

Asahi and Saint Gobain float glass Resistive Plate Chamber (RPC) detector materials are subjected to isochronal annealing treatment. To explore the temperature induced microstructural modifications in glass RPC detector materials, Positron annihilation lifetime spectroscopy (PALS), X-Ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopic investigations were performed. The positron lifetime parameters viz., o-Ps lifetime (τ3) and void size (Vf) increased significantly due to thermal expansion of SiOSi bonds in the regular tetrahedral structure of glass network. The significant increase in the void size of glass RPCs above 150 °C annealing temperature is attributed to the thermal vibrations of SiOSi bonds. The temperature induced electrical conductivity and activation energy is correlated with the positron lifetime parameters in both the float glasses. The thermally induced structural changes at higher annealing temperature are more in Saint Gobain glass than Asahi float glasses.

A portable muon telescope based on small and gas-tight resistive plate chambers.

We report on the first steps in the development of a small-size muon telescope based on glass resistive plate chambers with small active area (16 × 16 cm2). The long-term goal of this project is to focus on applications of muography where the telescope may have to be operated underground and/or inside small rooms, and in challenging logistic situations. Driving principles in our design are therefore compact size, light weight, gas tightness and robustness. The first data-taking experiences have been encouraging, and we elaborate on the lessons learnt and future directions for development.This article is part of the Theo Murphy meeting issue 'Cosmic-ray muography'.