Fabrication and Characterisation of Oil-Free Large High Pressure Laminate Resistive Plate Chamber

A large (240 cm $\times$ 120 cm $\times$ 0.2 cm) oil-free High Pressure Laminate (HPL), commonly referred as "bakelite", Resistive Plate Chamber (RPC) has been developed at VECC-Kolkata using locally available P-302 OLTC grade HPL. The chamber has been operated in streamer mode using Argon, Freon(R134a) and Iso-butane in a ratio of 34:57:9 by volume. The electrodes and glue samples have been characterised by measuring their electrical parameters like bulk resistivity and surface resistivity. The performance of the chamber has been studied by measuring the efficiency, its uniformity and stability in detection of cosmic muons. Timing measurement has been performed at a central location of the chamber. The chamber showed an efficiency $>$95$\%$ and time resolution ($\sigma$), at the point of measurement, $\sim$0.83 ns at 9000V. Details of the material characterisation, fabrication procedure and performance studies have been discussed.