OPERATION OF HIGH-RATE MICROSTRIP GAS-CHAMBERS

We describe recent measurements carried out in well controlled and rep roducible conditions to help understanding the factors affecting the s hort-and long-term behaviour of Microstrip Gas Chambers. Special care has been taken concerning the gas purity and choice of materials used in the system and for the detectors construction. Detectors built on g lasses with surface resistivity in the range 10(13)-10(15) Ohm/square have shown satisfactory performance as they do not show charging-up pr ocess at high rate and stand the large doses required for the future h igh luminosity experiments (similar to 10 mC.cm(-1).yr(-1)). Concernin g the lifetime measurements, it has been observed that chambers manufa ctured on high-resistivity glass are far more susceptible of suffering ageing than detectors made on low resistivity, electron-conducting su pports, independently of the metal used for the artwork (chromium or g old) at least in clean gas conditions. The successfully operation in t he laboratory of detectors manufactured on diamond-coated glass with a surface resistivity around 10(15) Ohm/square confirms the last statem ent. Results-from a long-term, high rate beam test are also reported.