High rate operation of micro-strip gas chambers

We describe the development of micro-strip gas chambers (MSGC) able to withstand the very high rates met in detectors for high luminosity experiments. A light and cheap mechanical assembly suited for mass-production of modules has been implemented. To prevent charging-up processes, affecting gain at high rates, we have tested substrates with surface resistivity in the range 10¹⁴-10¹⁵ Ω/□: stable gains at rates above 10⁶ mm^-2 s^-1 have been achieved at avalanche sizes of 10⁵ using electron-conducting and diamond-coated glass. A systematic search has been undertaken to define the purity levels of gas and materials necessary for long-term operation, with the goal of reaching a collected charge above 100 mC cm^-1 without degradation. This has been achieved operating in very clean conditions with argon-dimethylether. A dose-rate dependence of the ageing behaviour has been found alerting on the relevance of measurements realized at too high currents