Study of discharge properties in cascaded gaseous detectors

In this work we describe simulation and experimental studies of the possible reasons for the observed increase of the maximum gain in multi-GEM devices. Two main hypotheses are analyzed: first, a diffusion-dominated charge spread reducing the density in individual holes, acting as independent amplifiers and therefore an increase of the discharge limit with the number of cascaded electrodes; second, the possibility that total avalanche charge before transition to a discharge (Raether limit) strongly depends on the field value and is therefore much higher in cascaded than in single-stage systems.