Charge density as a driving factor of discharge formation in GEM-based detectors

Our experimental findings are in line with the well-grounded hypothesis of the charge density being the limiting factor of GEM stability against discharges. A detailed comparison of the measurements with GEANT4 simulations allowed us to extract the critical charge density leading to the formation of a spark in a GEM hole. This number is found to be within the range of (5−9)×106 electrons after amplification, and it depends on the gas mixture.