Irradiation and gas studies of micromegas production chambers for the ATLAS New Small Wheel

One of the main upgrades of the ATLAS Experiment during Long-Shutdown II is the replacement of the current forward muon spectrometer inner stations with a new detector, the New Small Wheel (NSW), covering the pseudorapidity region 1.3 < η < 2.7. Large area micromegas (micro mesh gaseous structure) detectors will be installed as part of the upgrade in order to cope with the high radiation environment expected from the Run III onwards while providing high resolution tracking capabilities. Such large micromegas detector size (up to 3 $m^{2}$) will be employed for the first time in high energy physics experiments, thus posing new challenges in terms of high-voltage and current stability. Before the installation within the ATLAS Detector, micromegas chambers are tested under irradiation at the CERN Gamma Irradiation Facility (GIF++).