Combination of two Gas Electron Multipliers and a Micromegas as gain elements for a time projection chamber

TL;DR

This paper presents a novel combination of Gas Electron Multipliers and Micromegas as amplification elements in a time projection chamber, aiming to reduce space charge buildup and dead time while maintaining good tracking and particle ID.

Contribution

It introduces a new configuration of gas amplification devices that effectively reduces ion back-flow and improves energy resolution in high-rate gaseous TPCs.

Findings

Ion back-flow below 0.4% at gain 2000

Energy resolution better than 12% at gain 2000

Effective suppression of space charge effects

Abstract

We measured the properties of a novel combination of two Gas Electron Multipliers with a Micromegas for use as amplification devices in high-rate gaseous time projection chambers. The goal of this design is to minimize the buildup of space charge in the drift volume of such detectors in order to eliminate the standard gating grid and its resultant dead time, while preserving good tracking and particle identification performance. We measured the positive ion back-flow and energy resolution at various element gains and electric fields, using a variety of gases, and additionally studied crosstalk effects and discharge rates. At a gain of 2000, this configuration achieves an ion back-flow below 0.4% and an energy resolution better than $\sigma/\text{E}=12\%$ for $^{55}$Fe X-rays.