Charge sharing in single and double GEMs

Abstract

Abstract The Gas Electron Multiplier (GEM) has become a widely used technology for high-rate particle physics experiments like COMPASS, LHCb and are going to be used for the upgrade of the detectors of other experiments, such as ALICE TPC. Radiation hardness, ageing resistance and stability against discharges are main criteria for long-term operation of such detectors in high-rate experiments. In particular, discharge is a serious issue as it may cause irreversible damages to the detector as well to the readout electronics. The charge density inside the amplification region is one of the limiting factors for detector stability against discharges. By using multiple devices, and thus sharing the electron multiplication in different stages, the maximum sustainable gain can be increased by several orders of magnitude. A common explanation for this is connected to the transverse electron diffusion, which causes widening of the electron cloud and reducing the charge density in the last multiplier. This has been verified experimentally [1] but numerical investigations, as far as we know, are scarce. In our work, we are using Garfield simulation framework as a tool to extract the information related to the transverse size of the propagating electron cloud and thus to estimate the charge density in the GEM holes for multiple stages. For a given gas mixture, we will present the initial results of charge sharing using single and double GEM detectors under different electric field configurations and its effect on other measurable detector parameters such as single point position resolution.