Study of the backside signal of micro-strip gas counters on electronic conducting glass

Microstrip gas counters (MSGC) on electronic conducting glass such as Schott S8900 have a very stable long-time behaviour. However, this glass is available in relatively thick plates only. A thick substrate limits the performances of two-dimensional detectors by attenuating the signal of the backside electrode which carries the second position coordinate. A structure with "open cathodes", where the central area of each cathode is non-metallized, reduces the screening effect. By increasing the cathode-backside potential difference, the backside signal increases considerably. Its amplitude becomes even equal to the anode signal when the cathodes are not connected to an external potential. As in the present mode the cathode strips do not contribute to the amplification process, this naturally leads to a structure where the cathodes are removed. Another advantage of this new structure design is the very high gas amplification which can be achieved. However, as the ions are discharged by a current through the substrate, the voltage drop caused by this current gives rise to counting rate dependence of the gas amplification.