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An experimental study to understand the physics behind charging-up of Gas Electron Multiplier (GEM)

Charging-up is a phenomenon observed while working with gaseous ionization detector having dielectric. It is comprised of two processes: the polarization of dielectric due to exposure to high electric field and collection of charges on dielectric surface. Both these charging-up processes affect the gain of the detector as they change the local field configuration around the dielectric. Here, we have studied these effects using experimental techniques for a single GEM detector. It has been observed that due to polarization the gain has increased following a curve similar to charging-up of a capacitor. However, the radiation charging-up has reduced gain depending on radiation rate. Here, the radiation rate has been modified by using a) collimators, b) strong and weak sources. As the rate has been increased, the rate of collection of charges on GEM dielectric has accelerated. Its effects are important for experiments where beam current changes significantly with time and in TPC application which requires gain to be stable over time.