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

Abstract

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. © 2019 IOP Publishing Ltd and Sissa Medialab.