Optical observation of discharge in resistive plate chamber

Pictures of the discharge in a resistive plate chamber (RPC) were taken usi ng a glass RPC, an image intensifier and a CCD camera. Measurements were se parately made for cosmic rays (trigger mode) and self-discharge (non-tigger mode), in vertical and horizontal views, operated in the streamer mode wit h various gas mixtures. Streamers are observed as narrow strings with diame ters <500 mu m, 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 detec tion efficiency, discharge patterns are similar for both the cosmic rays an d self-discharges. (C) 1999 Elsevier Science B.V. All rights reserved.