A study of factors limiting the maximum gain in microstrip gas counters

It was shown in our previous paper [1] that the maximum achievable gain in microstrip Gas Counters (MSGC's) is limited by surface streamers, which are self-quenched over a very limited voltage region and quickly transit to breakdown sparks. In this work we have tried to identify the main factors governing the maximum gain at which the streamers appear, and towards this end have made simulations and tested MSGC's of different geometries and on different substrates in both Ar- and Xe-based gas mixtures at pressures from 0.1 to 3 atm. From these studies we conclude that in order to reduce surface breakdowns in MSGC's, the multiplication should be concentrated to the narrowest region around the anode strips and the gas gain elsewhere, especially near the cathodes, should be maximally suppressed. For this purpose, narrow anodes and gas mixtures with proper Townsend coefficients should be used. Control experiments we performed confirm these hypotheses.