PERFORMANCE OF GAS MICROSTRIP CHAMBERS ON GLASS SUBSTRATA WITH ELECTRONIC CONDUCTIVITY

We present some recent measurements on Gas Microstrip Chambers (GMSC) realised on glass substrata with different bulk resistivity. Chambers manufactured on low resistivity supports ( approximately 109 Ohm.cm) have very high rate capability, up to and above 5 x 10(6) counts mm-2.s-1 at proportional gains around 10(3). With increase of resistivity of the support, the rate capability decreases, presumably because of the modification of electric field induced by the current flowing along the resistive surface, and at approximately 10(12) Ohm - cm the gain is affected already at the level of approximately 5 x 10(5) counts mm-2.s-1. Long term measurements of gain show a stable behaviour for the chambers built on low resistivity glass, up to an integral charge of approximately 130 mC per cm of strip. At normal operating conditions (an avalanche size of about 10(5) electrons) this corresponds to 10 Mrad of adsorbed dose for minimum ionizing particles, thus making the GMSC a good candidate for the use in LHC and SSC detectors. In order to reach the quoted lifetime, particular precautions have to be taken to guarantee gas purity. The present study has been realised in the framework of the collaboration for the Development of GMSC for Radiation Detection and Tracking at High Rates (CERN Research and Development Project RD28).