One of the main upgrades of the ATLAS Experiment at the Large Hadron Collider (LHC) during Long Shutdown 2 is the replacement of the current forward muon spectrometer inner stations with a new detector, the New Small Wheel (NSW), covering the pseudorapidity region $1.3 < \eta < 2.7$. 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 3 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++).