India-based Neutrino Observatory

Resistive Plate Chamber - R & D

The ICAL detector at INO will employ about 30,000 Resistive Plate Chambers (RPC) of about 2m x 2m in area as sensitive detector elements to track particles produced by the neutrino interactions inside the detector mass. Two collaborations are involved in the fabrication and study of these gaseous detectors. The group at VECC is involved in the study of Bakelite RPCs and the group at TIFR focuses on glass based RPC's.

RPCs are constructed by placing two glass plates parallel to each other and separated by a small gap. The separation is ensured by poly-carbonate button spacers placed in a grid like pattern. The four sides of the gap are then sealed. A suitable gas mixture, one which produces electron-ion pairs and thus a signal when an ionizing particle passes through, is flown through the gap by a gas mixing unit. The outer surfaces of the glass plates are coated with a conductive coating and a high electric field of about 10kV is applid across these electrodes.

The first activity in the R&D of RPCs at TIFR started with the development of a 30 RPC. Later a stack of 12 RPCs of 1m x 1m was develped which now serves as a cosmic-ray telescope. The final ICAL detector will have about 3 million electronic channels and hence a suitable test bench is necessary for testing of the electronics. The stack serves this purpose. The long term stability of these detectors is studied by constantly monitoring the noise rates and the efficiency of the detectors.

Detector related studies are complemented by cosmic muon studies. Recent studies include the directionality measurement of cosmic muons and the time offset calibration of the RPCs. The study of sealed RPCs is currently in progress and the preliminary results have shown encouraging results.

With the experience gained in the development of 1m x 1m RPCs, the group at TIFR progressed to fabricate 2m x 2m RPCs. The team was successful in the endeavor, with currently 5 RPCs in the new stack tracking cosmic muons. The photograph above shows the new stack in the INO-RPC lab at TIFR.

To enable mass production of RPCs for the ICAL detector the collaboration is now in the process of transferring the technology to the Industry. Some glass factories were approached and their personnel are trained in the fabrication and quality control of the RPCs. Industries are also consulted fo rthe production of the conductive paints. Recently, an industrial technique was developed to screen-print the glasses and for the consequent curing of the same. Other areas where we seek industrial interface is the production/design of the pick-up panels of the RPCs. Bakelite RPCs developed by the VECC group at Kolkata are also studied simultaneously. The stack at VECC consists of 8 glass RPCs and 4 Bakelite RPCs. .


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