Optical observation of discharge in resistive plate chamber

Pictures of the discharge in a resistive plate chamber (RPC) were taken using a glass RPC, an image intensifier and a CCD camera. Measurements were separately made for cosmic rays (trigger mode) and self-discharge (non-tigger mode), in vertical and horizontal views, operated in the streamer mode with various gas mixtures. Streamers are observed as narrow strings with diameters <500 μm, extending between the anode and the cathode surfaces. Each streamer accompanies disk-shaped discharges of 2–4 mm diameter, on both the cathode and the anode surfaces. With a gas mixture that gives a high detection efficiency, discharge patterns are similar for both the cosmic rays and self-discharges.