OPTIMIZATION OF MICROSTRIP GAS CHAMBER DESIGN AND OPERATING-CONDITIONS

We discuss recent experimental and theoretical work aimed at optimizin g the structure and operating conditions of microstrip gas chambers. I n a systematic set of measurements we have found gas mixtures allowing high stable gains; the best results were obtained using argon-dimethy lether in equal percentages (50-50), and mixtures of dimethylether and carbon dioxide. Detectors exhibit lower noise and better energy resol ution when using high drift fields, i.e. above 5 kV/cm; in these condi tions, stable gains in excess of 10(4) could be achieved. We also disc uss a model to characterize the breakdown depending on the combined fi eld strength at the edges of the anode and cathode strips; using a pro gram that computes fields and gains and applying the discharge criteri on, we have estimated the optimum geometry of the detectors. The resul ts indicate that higher gains before discharges can be obtained for wi de cathodes: as an example, for 10 mum anodes we predict an increase b y a factor of 4 of the maximum gain when increasing the width of the c athode strips from 80 mum to 160 mum.