Preliminary studies on GEM foil degradation in harsh radiation environments
2019 August 26
Several High Energy Physics experiments are adopting Gaseous Electron Multipliers (GEMs) in substitution for the Multi-Wire Proportional Counters (MWPC) either in upgrade plans or in the design stage. Most of the cases, the interest lies in the high count rate capabilities of GEMs together with good spatial resolution. Because of all this interest on GEMs for high count rates measurements, it is important to evaluate the degradation of its constituent materials under such circumstances. This work aims to bring insights from material science to that matter. For this, we studied two possible effects that may play some role in the degradation process of the GEM foils in a harsh radiation environment: One of them is the Kapton degradation due to energy deposition by ionization, which is an effect expected to be triggered by highly energetic particles. We degraded a Kapton foil using 2.2 MeV He+ ions. At this energy, the electronic stopping dominates the interaction processes, thus depositing energy by sequences of ionization. The Kapton composition was assessed by real-time nuclear scattering spectrometry, revealing the Hydrogen losses as the major effect. The second process considered in this study is the erosion of the Copper clad. Opposite to the Kapton degradation, the Copper clad erosion is expected to be induced by low energy ions associated with a sputtering process of the Copper. These low energy ions are expected to be generated during the avalanche of ionization in the amplification process. This effect was explored by computer simulation using the Garfield++ library and estimates of sputtering yields.