Characterization of a glass GEM for sealed detectors application and reduction of charging-up effects

Apart from high energy physics experiments, there has been a great effort in recent years to incorporate MPGDs in many other applications i.e. medical treatments and imaging and home land security. However, MPGDs (as most gaseous detectors) are normally operated under a constant flushing of the gas. Their use thus turns them expensive since they rely on a constant gas supply and a suitable infrastructure, but most important is the loss of their portability. These reasons have pushed the community to search for other solutions, aiming for the development of sealed detectors. The demands for such is to be made out of low outgassing rate materials and possibly the use of only noble gas to avoid aging due to chemical activity of the ionized gas of the avalanche. The default material for GEM detectors - Polyimide (Kapton), is not suitable for a sealed detector because of its high outgassing rate, thus calling for new solutions. Moreover, GEMs, being essentially made out of an insulating material, pose a problem in terms of their charging up. When a field line inside the holes of the GEM ends not outside it but on the insulator, an avalanche electron might hit the hole wall and stick to the insulator. These electron do not have a "draining" path and are therefore left inside the hole, thus altering the field configuration and consequentially the behavior of the detector. It has long been proposed to use high resistivity materials instead of insulating to produce a conductive path through which these electrons could be drained, reducing the charging up effect.