Simulation studies of charging-up effect for single GEMs

Abstract

Many experiments revealed a charging-up effect inside the Gas Electron Multipliers (GEMs) holes, resulting in variation of GEM effective gain. Charge accumulation on the insulator surface inside the GEM hole (charge process) is involved in the present simulation models. With only the charge process in the simulation, a longer and larger gain stability of GEM was observed while comparing the charging-up curves to references, even distinct in the relatively high conductivity of GEM insulator. This observation indicates that charge transportation within the GEM insulator (discharge process) is non-negligible; the charging-up stability depends on the dynamic balance of the charge and discharge process. Therefore, a discharge model is induced and expressed by a piecewise function based on the presence of a simulation framework. Charging-up curves are compared for single GEMs with two different structures under different gain values and input flux; the trend from simulation with the discharge process is consistent with those from references. Although the deviation of simulated charging-up curves is observed at the region started to be stable, indicating improvements in the discharge formulation, it can still predict the trend of stability and values of GEM effective gain. This study improves the present simulation model of the charging-up effect for single GEMs and provides a reference for other charging-up models.