Simulation of the dielectric charging-up effect in a GEM detector

Abstract

a b s t r a c tThe charging up effect is well-known in detectors containing dielectric materials and it is due to electrons and ions liberated in an avalanche and collected on the dielectric surfaces. In particular in Gas Electron Multiplier (GEM) based detectors, charges can be captured by the Kapton that separates top and bottom electrodes. The collection of a substantial number of charges on the dielectric surfaces induces a modification of the field inside the GEM holes that implies important consequences on some fundamental parameters such as the electron transparency and the effective gain. The correct simulation of this effect opens new ways to the detailed study of the processes that happens in a GEM-based detector and gives the possibility to optimise the GEM geometry in order to avoid it. This paper compares results of the measurements and the simulations, with and without the introduction of the charging-up effect, of the GEM electron transparency in the case of a single GEM detector. The introduction of the charging up effect in the simulation resulted to be crucial in order to get the proper agreement with the measurements. The measurements and simulations of the GEM effective gain will be the subject of a future work.

The gas electron multiplier (GEM): Operating principles and applications

“…The gain shifts due to charging up of the insulators have been extensively studied with computer models [16,58].…”

“…43 is an example of measured gain as a function of rate for a Triple-GEM detector at increasing values of total effective gains (unpublished results from [78]). Simulation studies have attempted to reproduce this peculiar behavior [58]. These extreme rates are only met in special applications, as beam and soft X-rays plasma diagnostics, where gain uniformity is often not a major concern [79,80].…”

Optical quality assurance of GEM foils

“…Secondary electrons and ions created in the avalanche continue to drift in the detector. The shape of the electric field near and inside the holes plays an important role in several key characteristics of GEM foils, such as electron transparency, ion feedback and rate dependent charge-up properties [2][3][4][5]. The field shape depends on the shape of the hole.…”

Study of solid-conversion gaseous detector based on GEM for high energy X-ray industrial CT

“…The GEM consists of a metal-insulator-metal thin-foil composite, chemically pierced with a high density of holes, typically 50-100 μm in diameter at Fig. 4) [12]. When a suitable voltage is applied on the GEM electrodes, a very strong electric field (above 40kV/cm) arises within the holes, where the gas amplification process takes place (shown in Fig.…”

“…Particularly, several novel gas-type gaseous detectors have received considerable attention over the past few years which include: gas electron multiplier (GEM) [11,12], microstrip gas chamber (MSGC) [12], and various combinations of MSGC and GEM detectors [13]. In spite of the good performance, however, the above-described detectors were primarily developed primarily for usage in detecting either low energy radiation, or very high energy particles in particle accelerators.…”