Gain uniformity of trapezoidal triple-GEM detectors

The Triple Gas Electron Multiplier (Triple-GEM) became recently one of the most popular gaseous ionization detectors used in high energy physics. Together with the experimental tests, the Monte Carlo simulation is a very important tool for the understanding of the properties of the triple-GEMs. The electron gain has to be stable and uniform enough across the detector. In this paper it is proposed to study the gain and its uniformity in a triple-GEM detector of a trapezoidal shape. It also reports on the uncertainty which can occur during the construction or the operation processes and can result in a gain variation.