Discharge studies and prevention in the gas electron multiplier (GEM)

The gas electron multiplier (GEM) used as single proportional counter or in a cascade of two or more elements, permits to attain high gains and to perform detection and localization of ionizing tracks at very high radiation rates. As in other micro-pattern detectors, however, the occasional occurrence of heavily ionizing trails may trigger a local breakdown, with possible harmful consequences on the device itself and on the readout electronics. This paper describes a systematic investigation of the discharge mechanisms in single and multiple GEM structures, and suggests various strategies to reduce both the energy and the probability of the discharges.