Hole Misalignment and Gain Performance of Gaseous Electron Multipliers

TL;DR

This paper investigates how hole misalignment in GEM foils affects their gain performance, highlighting the importance of precise mask alignment during manufacturing and demonstrating the use of optical scanning for quality control.

Contribution

It reveals the critical impact of mask misalignment on GEM gain and showcases the Helsinki optical scanner as an effective tool for quality assessment.

Findings

Hole misalignment significantly reduces GEM gain

Optical scanner can accurately measure hole dimensions and alignment

Proper mask alignment is crucial for optimal GEM performance

Abstract

It is well known and has been shown that the gain performance of Gaseous Electron Multipliers (GEM) depends on the size of the holes. With an optical scanner it is possible to measure the dimensions of the holes, and to predict the performance of GEMs. However, the gain prediction of GEMs that are manufactured with a double mask etching technique is not straightforward. With the hole size information alone, it is not possible to make precise prediction of the gain. We show that the alignment of the photo-masks between the two sides of the GEM foils plays a crucial role. A misalignment of a few microns can lower the gain substantially. The study is performed by using the Helsinki high definition optical scanner for quality control of GEM foils, and this will show its true potential.