A dynamic method for charging-up calculations: the case of GEM

P M M Correia,R Veenhof,M Varun Nemallapudi,C D R Azevedo,J F C A Veloso,C A B Oliveira,A L M Silva

doi:10.1088/1748-0221/9/07/p07025

Abstract

The simulation of Micro Pattern Gaseous Detectors (MPGDs) signal response is an important and powerful tool for the design and optimization of such detectors. However, several attempts to exactly simulate the effective gas gain have not been completely successful. Namely, the gain stability over time has not been fully understood.Charging-up of the insulator surfaces have been pointed as one of the responsible for the difference between experimental and Monte Carlo results.This work describes two iterative methods to simulate the charging-up in one MPGD device, the Gas Electron Multiplier (GEM).The first method, which uses a constant step size for avalanches time evolution, is very detailed but slow to compute.The second method instead uses a dynamic step-size that improves the computing time. Good agreement between both methods was achieved.Comparison with experimental results shows that charging-up plays an important role in detectors operation, explaining the time evolution of the gain. However it doesn't seem to be the only responsible for the difference between measurements and Monte Carlo simulations.

Highlights

A considerable amount of work has been done over the last few years to improve the simulations of Micro Pattern Gaseous Detectors (MPGDs)
In order to accelerate the simulation process, we developed an extended method that uses a dynamic step-size in each iteration
The sum of all electric charges deposited in the insulator surface, per primary avalanche, is shown in figure 6a for both methods, as function of the charge produced by each avalanche, per hole

Summary

Introduction

A considerable amount of work has been done over the last few years to improve the simulations of MPGDs. The number of simulated avalanches is correlated with the number of primary electrons that undergo to the hole, since we assume that no charges will drift in the insulator. The distribution of new electrons and ions that reaches the insulator tend to compensate each other, due to Coulomb attraction between previous and future deposited charges (figure 2b).

Results

Conclusion