Simulation of gain stability of THGEM gas-avalanche particle detectors

Abstract

Charging-up processes affecting gain stability in Thick Gas Electron Multipliers (THGEM) were studied with a dedicated simulation toolkit. Integrated with Garfield++, it provides an effective platform for systematic phenomenological studies of charging-up processes in MPGD detectors. We describe the simulation tool and the fine-tuning of the step-size required for the algorithm convergence, in relation to physical parameters. Simulation results of gain stability over time in THGEM detectors are presented, exploring the role of electrode-thickness and applied voltage on its evolution. The results show that the total amount of irradiated charge through electrode's hole needed for reaching gain stabilization is in the range of tens to hundreds of pC, depending on the detector geometry and operational voltage. These results are in agreement with experimental observations presented previously.

Measurements of charging-up processes in THGEM-based particle detectors

“…In both simulation and the measurement, the characteristic time is proportional to the inverse of the detector's gain. The "characteristic charge" estimated from the measured "characteristic time" vs the detector's gain, is also found consistent with that simulated for Ar-based mixtures (of order of hundreds of pC) [13].…”

“…The simulations of the charging-up of the detector's electrode, and the calculations of the avalanchegain variations were performed using the recently developed simulation tool for THGEM-based detectors [13]. It consists of an iterative algorithm and is based on the superposition principle [12].…”

“…It corresponds to the number of avalanches considered in each iteration before changing the field configuration. (see [13] for more details).…”

“…In this work, an experimental study has been carried out in different THGEM-electrode configurations (e.g. electrode holes with and without etched rims), different irradiation conditions and different gases -to validate the model-simulation results [13]. The experimental setup and methodologies are detailed in section 2; they are followed, by an extensive comparison of the measured and simulated gain-stabilization results, under different experimental conditions (section 3) and a detailed study of the hole-rim effects (section 4).…”

Electron transport and electric field simulations in two-phase detectors with THGEM electrodes

“…It is worth mentioning previous works on simulation of the electric fields and electron transport in THGEM-like structures in the gas phase: [11,12,13,14]. To the best of our knowledge, no one has simulated THGEM performance in liquid argon thus far; it has been done for the first time in the present work.…”