Operation Of Resistive Plate Chambers Research Articles

Numerical qualification of eco-friendly gas mixtures for avalanche-mode operation of resistive plate chambers in INO-ICAL

Proposition and qualification of an eco-friendly gas mixture of Ar(5%):CO2(60%): N2(35%) for operating Resistive Plate Chambers of INO-ICAL experiment in avalanche mode is the soul of this work. The detector efficiency and streamer probability for the proposed mixture have been simulated using a hydrodynamic model developed by us. Efficacy of the mixture has been studied by comparing the simulated results to available experimental data for the standard gas mixture of R134a(95.2%):i-C4H10(4.5%):SF6(0.3%) to be used in INO-ICAL, as well as the same observables measured for other eco-friendly hydrofluoroolefin (HFO1234ze)-based potential replacements. To reduce the streamer probability of the proposed argon-based gas mixture at higher voltages, the usual practice of adding a small amount of electronegative gas SF6 has been tested. An alternative approach of lowering electronic threshold has been investigated as well for the same purpose.

Characterization of tetrafluoropropene-based gas mixtures for the Resistive Plate Chambers of the ALICE muon spectrometer

The muon identification system of the ALICE experiment at the CERN LHC is based on Resistive Plate Chamber (RPC) detectors. These RPCs are operated in the so-called maxi-avalanche mode with a gas mixture made of tetrafluoroethane (C2H2F4), sulfur hexafluoride (SF6) and isobutane (i-C4H10). All of these components are greenhouse gases: in particular, the first gas is already phasing out of production, due to recent European Union regulations, and its cost is expected to increase in the near future. Therefore, finding a new eco-friendly gas mixture has become extremely important in order to reduce the impact of the RPC operation on the environment, and for economic reasons. Due to the similar chemical structure, hydrofluoroolefins appear appropriate candidates to replace C2H2F4 thanks to their very low GWPs, especially tetrafluoropropene (C3H2F4) with the trade name HFO1234ze(E). In order to identify an eco-friendly gas mixture fulfilling the requirements for operation in the ALICE environment in the coming years, a dedicated experimental set-up has been built to carry out R&D studies on promising gas mixtures. Measurements have been performed with a small-size RPC equipped with the front-end electronics, providing signal amplification, developed for ALICE operation at high luminosity after the LHC Long Shutdown 2. HFO1234ze(E)-based mixtures with the addition of CO2 are discussed in this paper as well as the role of i-C4H10, as quencher, and SF6, as strong electronegative gas, in such mixtures.

Study of flow and control of gas mixture for the Resistive Plate Chamber (RPC)

The upcoming underground INO-ICAL experiment will be instrumented with 28,800 of RPCs (glass based electrode of 3 mm thick) of size (1.85× 1.74) m2, which are the active elements and the key goal of the ICAL is to precisely measure the neutrino(s) mass. The RPCs are operated in the avalanche mode, using a gas mixture of R134a (95.2%), I-Butane (4.5%) and SF6 (0.3%). The number of RPCs that would be used is large with a total volume of gas of ∼ 200 m3, a Closed Loop gas mixing System (CLS) is mandatory. The performance of the RPCs depends on various parameters namely, the environmental conditions such as atmospheric pressure, ambient temperature, humidity etc., flow rate of gas mixture into the RPCs, concentration of the gas mixture (should be maintained constant throughout the operation), quality of gas, the RPC input gas pressure, uniformity of conductive coating on the surface, uniform gas gap thickness, nozzle positions, electrode thickness, ageing etc. We have tried to achieve the optimum flow rate of gas mixture (few SCCM) into the RPCs in the CLS without deteriorating the performance of the RPC. A modest low flow rate is ideal due to the usage of glass as electrodes and low back ground radiation (low cosmic rays only) unlike CERN-CMS experiments where the electrodes used are of Bakelite and are operated under high radiations with flow rates of few litres per hour. In this paper we present the flow resistors that are fabricated (capillary) and are suitable for final ICAL RPCs, the primitive simulation studies done to understand the distribution of the flow of gas mixture inside an RPC and also the behaviour of gas flow with different position of the input gas nozzles of an RPC. We also conclude here with results of the safe operating pressure parameters required for the operation of ICAL RPC in the CLS.

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.

Characterization of RPC operation with new environmental friendly mixtures for LHC application and beyond

The large muon trigger systems based on Resistive Plate Chambers (RPC) at the LHC experiments are currently operated with R134a based mixture. Unfortunately R134a is considered a greenhouse gas with high impact on the enviroment and therefore will be subject to regulations aiming in strongly reducing the available quantity on the market. The immediat effects might be instability on the price and incertitude in the product availability. Alternative gases (HFO-1234yf and HFO-1234ze) have been already identified by industry for specific applications as replacement of R134a. Moreover, HFCs similar to the R134a but with lower global warming potential (GWP) are already available (HFC-245fa, HFC-32, HFC-152a). The present contribution describes the results obtained with RPCs operated with new enviromemtal friendly gases. A particular attention has been addressed to the possibility of maintening the current operation conditions (i.e. currently used applied voltage and front-end electronics) in order to be able to use a new mixture for RPC systems even where the common infrastructure (i.e. high voltage and detector components) cannot be replaced for operation at higher applied voltages.

Strategies for reducing the environmental impact of gaseous detector operation at the CERN LHC experiments

A wide range of gas mixtures is used for the operation of different gaseous detectors at the Large Hadron Collider (LHC) experiments. Nowadays some of these gases, as C2H2F4, CF4 and SF6, are indicated as greenhouse gases (GHG) and dominate the overall GHG emission from particle detectors at the LHC experiments. The release of GHG is an important subject for the design of future particle detectors as well as for the operation of the current experiments. Different strategies have been adopted at CERN for reducing the GHG emissions. The standard approach is the recirculation of the gas mixture with complex gas systems where system stability and the possible accumulation of impurities need to be attentively evaluated for the good operation and safety of the detectors. A second approach is based on the recuperation of the gas mixture exiting the detectors and the separation of its gas components for re-use. At long-term, the use of less invasive gases is being investigated, especially for the Resistive Plate Chamber (RPC) systems. Operation of RPC with environmentally friendly gas mixtures is demonstrated for streamer mode while avalanche mode operation needs more complex gas mixtures.

Optimization of a closed-loop gas system for the operation of Resistive Plate Chambers at the Large Hadron Collider experiments

Abstract Resistive Plate Chambers (RPCs), thanks to their fast time resolution (∼1 ns), suitable space resolution (∼1 cm) and low production cost (∼50 €/m 2 ), are widely employed for the muon trigger systems at the Large Hadron Collider (LHC). Their large detector volume (they cover a surface of about 4000 m 2 equivalent to 16 m 3 of gas volume both in ATLAS and CMS) and the use of a relatively expensive Freon-based gas mixture make a closed-loop gas circulation unavoidable. It has been observed that the return gas of RPCs operated in conditions similar to the difficult experimental background foreseen at LHC contains a large amount of impurities potentially dangerous for long-term operation. Several gas-cleaning agents are currently in use in order to avoid accumulation of impurities in the closed-loop circuits. We present the results of a systematic study characterizing each of these cleaning agents. During the test, several RPCs were operated at the CERN Gamma Irradiation Facility (GIF) in a high radiation environment in order to observe the production of typical impurities: mainly fluoride ions, molecules of the Freon group and hydrocarbons. The polluted return gas was sent to several cartridges, each containing a different cleaning agent. The effectiveness of each material was studied using gas chromatography and mass-spectrometry techniques. Results of this test have revealed an optimized configuration of filters that is now under long-term validation. Gas optimization studies are complemented with a finite element simulation of gas flow distribution in the RPCs, aiming at its eventual optimization in terms of distribution and flow rate.

Simulation of temperature dependence of RPC operation

The effect of ambient temperature on the performance of a resistive plate chamber (RPC) has been studied by simulating the avalanche development inside the gas gap and considering the temperature variations of avalanche parameters and the plates’ resistivity. For both avalanche and streamer modes of operation, it is shown that the induced signal increases with ambient temperature and the charge spectrum shifts toward higher charge values. The results of simulation at low particles rates show that the temperature dependency originates just from the variations of avalanche characteristics with temperature. The simulation clearly reconfirms the experimental fact that the detector efficiency is a function of scaled high voltage with temperature. The simulation results at high particles flux densities show that the strong degradation of plates’ resistivity with temperature improves the efficiency and rate capability of the detector in agreement with available experimental reports.

Gas mixture studies for streamer operation of Resistive Plate Chambers at low rate

Gas mixtures have been studied in order to be used in the Resistive Plate Chambers (RPCs) of the OPERA spectrometers. We are interested in mixtures with a low R-134a concentration in order to reduce the streamer charge and the operating voltage without spoiling the usual RPC performances.

SF6 quenched gas mixtures for streamer mode operation of RPCs at very low voltages

In the present paper we describe a search for gases that allow to reduce the energy of the electrical discharge produced in Resistive Plate Chambers (RPCs) operated in streamer mode, by reducing both the operating voltage and the released charge. This can be achieved, with current gas mixtures of argon, tetrafluoroethane (TFE) and isobutane, by reducing the total amount of quenching components (TFE+isobutane) down to 10–15% and compensating for the lower gas quenching power with the addition of small amounts of SF6: We show here that SF6; even for concentrations as low as 1% or less, has a strong effect in reducing the delivered charge in low quenched gases and allows to achieve a proper working mode of the RPC even at voltages as low as 4–5kV over a 2 mm gas gap. r 2002 Elsevier Science B.V. All rights reserved. PACS: 29.40.Cs

Test of freonless operation of resistive plate chambers with glass electrodes—[formula omitted] gas gap vs [formula omitted] gas gap

Non-freon gas mixtures (Ar/iso-C4H10) were tested as the chamber gas for 1 and 2mm gas gap Resistive Plate Chambers (RPCs) with float glass as the resistive electrodes, operated in the streamer mode. With the narrower (1mm) gas gap, streamer charge is reduced (∼1/3), which reduces the dead time (and dead area), associated with each streamer, improving the detection efficiency. The best performance was obtained for two cases: Ar/iso-C4H10=50/50 and 60/40. For the 50/50 mixture, a detection efficiency of better than 98% was obtained for the 1mm gap RPC, while the efficiency was 95% for the 2mm gap RPC, each operated as a double-gap RPC. The measured time resolution (rms) was 1.45±0.05(2.52±0.09)ns for the 1(2)mm gap RPC for the 50/50 mixture.

Study on the operational conditions of a double-gap resistive plate chamber for the CMS

We present the results from cosmic ray tests on the forward Resistive Plate Chamber (RPC) for the CMS. Double-gap prototype RPC were built and tested in the Korea Detector Laboratory (KODEL). We found that addition of SF 6 and water vapor to the tetrafluorethane-based gas mixture was required for the long-term stable operation of RPC. Efficiency, time resolution as well as cross-talk behavior of the detector were investigated. In addition, we present the temperature and humidity dependence of bulk resistivity of Korean bakelite in detail.

Study of avalanche mode operation of resistive plate chambers with different gas gap structures

The operation of narrow gap, wide gap and multigap resistive plate chambers in an avalanche mode was studied. No advantage in avalanche–streamer separation was found for the wide gap and multigap chambers operating with Ar-based mixture as compared with the narrow gap chamber. For dense tetrafluoroethane-based mixture, proportionality was observed between streamer-free plateau width and total gas thickness, in rough agreement with corresponding shift of the maximum of avalanche charge distributions from zero. The best result was obtained for double-gap chamber with the read-out electrode located between two subgaps.

Properties of C 2H 2F 4-based gas mixture for avalanche mode operation of resistive plate chambers

Some properties of a 90% C 2H 2F 4 gas mixture, used to operate resistive plate chambers in the avalanche mode, are determined by comparing the experimental results with the prediction of simple analytical calculations. The fast charge distribution of the signal induced on pick-up electrodes is reproduced by means of a Monte Carlo simulation of the avalanche development. In addition, predictions for a gas mixture with poor content of C 2H 2F 4 are given for comparison.

Avalanche and streamer mode operation of resistive plate chambers

A resistive plate chamber was operated at voltages increasing in steps of 200 V over a 3 kV interval and the transition between the avalanche and streamer modes was studied. The avalanche amplitude was observed to be exponentially dependent on the operating voltage up to a value, characteristic of the gas, where the avalanche saturation occurs and delayed streamer signals start to appear. Signal waveforms, charge and timing distributions are reported.

Further studies of avalanche mode operation of resistive parallel plate chambers

We have investigated the high rate operation of the resistive plate chamber and have discovered that melamine-phenolic laminates are good candidates for a plate material. We have previously shown that avalanche mode (rather than spark mode) gives a substantial improvement in the rate capability. There are two new encouraging results; the timing spectra are not affected by the rate; and particles at non normal incidence have a higher detection efficiency; these substantially increase the rate capability of this device. However there are two results that show that further R&D is needed. These are: the change in resistivity of the plate material with time; and the fall off of the efficiency with increasing high voltage. Our goal is to produce a cheap large area detector that has good spatial and time resolution and has a rate capability suitable for the muon system at a future collider. We believe that these results show that this detector is already promising and should satisfy these requirements with further R&D.