Charging up studies in thick Gas Electron Multipliers

Gaseous ionization detectors that have insulating media exposed to the active gas volume have issues related to charging up of the insulators during the course of its use[1]. The time-dependent variation of detector response in hole-based Micro-Pattern Gaseous Detectors (MPGDs), especially THick Gas Electron Multipliers (THGEMs), is one of the challenging problems that has been attributed to "charging up" and "charging down". Experimental studies of stabilization of THGEM gas gain with time in argon-based mixtures under various experimental conditions will be presented here. Effects of different sources with varying irradiation rates on the gain saturation process have been studied. It has been observed that low-rate source shows two-step gain stabilization phenomena, one short-term saturated gain, another long-term saturated gain, whereas high-rate source shows just one-step gain saturation. While this two-step stabilization has been attributed to the charging up of the rim by earlier studies, its effect seems to be subdued for high-rate irradiation according to the present studies. The results provide an insight into the dynamics of gain saturation in THGEMs.