Simulation of multi-layer GEM from single to triple GEMs

Originally Micro-Pattern Gas Detectors (MPGDs), a type of gaseous ionization detector, were developed for high energy physics experiments, however applications have expanded to astrophysics, neutrino physics, neutron detection, and medical imaging. Over the past 20 years this led to the development of novel MPGD devices: the Micro-Strip Gas Chamber (MSGC), Gas Electron Multiplier (GEM), Micromegas (a type of MPGD using a parallel-plate micro-mesh avalanche counter), and many others, revolutionizing cell size limits for many gas detector applications and considerably improving reliability and radiation hardness. In a gaseous detector, a particle (or an energetic photon) enters a gas cell and collides with an atom of gas, which emits a high energy electron. This electron undergoes further collisions which creates an ionization tract whose electrons are drifted by a small electric potential across a gas cell onto a bottom plate consisting of a double layered conductor separated by an insulator with a strong electric field (50-70 kV/cm) difference between them. This bottom plate, called a Gas Electron Multiplier (GEM), has an array of tiny holes and the ionization tract electrons fortunate enough to pass though the holes are strongly accelerated causing them to create secondary cascades in the direction of a pixel readout array such as the complementary metal-oxide-semiconductor application-specific integrated circuit (CMOS ASIC) chip. With a multi-GEM layer structure, of up to 5 layers, a very high effective gain (up to 106 with some gases) can be attained with each GEM layer working at an individually much lower gain thus avoiding discharge problems. This is the major advantage of the GEM technology. In many groups, triple GEM (3 layers of GEMs) designs have been extensively studied in both experiments and simulations. Here, we will present a simulation study of single, double, and triple GEMs's to characterize their properties such as gain, spatial resolution, energy resolution, efficiency, and so on using Garfield++ and ANSYS field solver and compare between the results of published experiments and simulations.