Investigation of Ion Backflow in Bulk Micromegas Detectors

TL;DR

This paper investigates ion backflow in bulk Micromegas detectors, measuring its dependence on design parameters and comparing results with detailed simulations, including the impact of a second micro-mesh.

Contribution

It provides new experimental measurements of ion backflow fractions and compares them with advanced numerical simulations, exploring the effect of a second micro-mesh.

Findings

Ion backflow fraction varies with detector design parameters.

Simulations closely match experimental measurements.

Using a second micro-mesh reduces ion backflow.

Abstract

The operation of gas detectors is often limited by secondary effects, originating from avalanche-induced photons and ions. Ion backflow is one of the effects limiting the operation of a gas detector at high flux, by giving rise to space charge which disturbs the electric field locally. For the Micromegas detector, a large fraction of the secondary positive ions created in the avalanche can be stopped at the micro-mesh. The present work involves measurements of the ion backflow fraction (using an experimental setup comprising of two drift planes) in bulk Micromegas detectors as a function of detector design parameters. These measured characteristics have also been compared in detail to numerical simulations using the Garfield framework that combines packages such as neBEM, Magboltz and Heed. Further, the effect of using a second micro-mesh on ion backflow and other parameters has been studied numerically.