Development and qualification of triple-GEM detector built with large size single mask foils produced in India

Abstract

The Gas Electron Multiplier (GEM) is the new age detector for nuclear and particle physics experiments, which was first developed by the European Center for Nuclear Research (CERN). It is comprised of an excellent insulator (Kapton/Apical) having a thickness of 50 µm which is covered with 5 µm copper layer on both sides and pierced by a regular array of holes. From its invention, CERN has been the sole supplier of the GEM foils until recently when few private companies started manufacturing GEM foils under the transfer of technology (TOT) from CERN. However, it's a long process to validate the foils delivered by these companies to claim that the GEM detectors made from them are compatible with high scientific standards. Along these lines, an India based company Micropack Pvt. Ltd. began fabricating both double and single mask GEM foils; at first Micropack produced 10 × 10 cm 2 double mask foils which were tested both at foil and detector level by University of Delhi (DU) and it was confirmed to satisfy the required standards. Because of the double mask technique, the size of the GEM foil was constantly constrained so to overcome the confinement in size of GEM foils the single mask technique was developed in 2010. Micropack produced the first batch of 30 × 30 cm 2 single mask foils in a joint effort with DU. A triple-GEM detector was constructed using these foils to test the fundamental quality controls, which include effective gain measurement, energy spectrum, and gain uniformity. Along with this, we will also report on the few advance studies which include discharge probability, rate capability, and charging up for this detector and foils.

The qualification of GEM detector and its application to imaging

“…While keeping the detector at a constant 700 μA of divider current and X-ray flux constant over the period of time we observed variations in gain and stability over the course of 30 hours. In previous study we have seen the flux has almost no impact on the gain of the detector [12,29] when it becomes stable after few hours. Figure 11 illustrates the changes in gain over time.…”