PERFORMANCE OF MSGC ON ELECTRONICALLY AND IONICALLY CONDUCTIVE SUBSTRATA IN VARIOUS OPERATIONAL CONDITIONS

Recent measurements realized with Microstrip Gas Chambers (MSGC) manufactured on glass substrata in a range of bulk resistivity are presented. Chambers made on electronically conductive supports with resistivity of 10(9) OMEGA cm and gold strips show a stable behaviour during long term irradiation up to an accumulated charge of 130 mC/cm of strip when operated in an argon-dimethylether (DME) mixture. Similar measurements realised with argon-methane show instead a fast degradation of gain already at collected charge of around 5 mC/cm. Further investigation of MSGC performance with different Ar-DME compositions show that the larger stable gain can be achieved with a 50-50 mixture. We present also results of beam runs performed with MSGC manufactured on Hoya SL glass with an anode to cathode distance of 200 mum and a 2 mm gas layer. The dependence of efficiency and spatial resolution on the incidence angle of track was measured with argon-DME and xenon-DME gas mixtures; for minimum ionizing particles perpendicular to the chambers (0-degree) the spatial resolution for Xe gas mixture is 65 mum rms and the efficiency 98%. For incidence angles up to 10-degrees a small degradation of both parameters was observed.