Numerical analysis for GEM signal and time resolution

Abstract

We have investigated the gas electron multiplier (GEM) signal and time resolution using a numerical analysis method. The Garfield\(++\) simulation package with a known field solver, ANSYS, is used here. To examine the impacts of gas mixture and electron transport characteristics inside the detector, two other softwares, Magboltz and Heed, were utilised. By exploring the effects of detector geometry, electric fields, incoming particle energy and gas mixture characteristics, we tried improving GEM detectors for higher temporal resolution. A single GEM detector was investigated with two radiation sources, i.e., a 5.9 keV \(\hbox {Fe}^{55}\) X-ray photon and cosmic muons with energies ranging from 1 MeV to 1 TeV. With Ar:\(\hbox {CO}_2\) gas mixture for a particular set-up, a minimum time resolution of up to around 4 ns was recorded. This number can be reduced even more by using various detector geometries and field settings. A significant result in lowering the temporal resolution was achieved by changing the drift field and percentage of the ionisation component in the gas mixture. The admixture of \(\hbox {O}_2\) and \(\hbox {N}_2\) in the gas medium also improved the detector time performance. It was also observed that the initial particle energy has little effect on the timing accuracy of the detector.