The Micromegas Construction Project For the ATLAS New Small Wheel

Large scale Micromegas (Micro mesh gaseous structure) detectors will be installed as part of the upgrade of the ATLAS innermost layer of the muon spectrometer end-cap regions, known as new the small wheel (NSW), in order to cope with the high radiation environment expected from the Run III onwards while providing tracking capabilities with high spatial resolution. Such a large Micromegas detector size (up to 3 m$^2$) will be employed for the first time in high energy physics experiments. Each wheel will have eight detector planes, divided into two quadruplets, in order to provide tracking redundancy. Each Micromegas quadruplet will have two readout planes for the reconstruction of the precision coordinate and two with stereo reading ($\pm$1.5 degrees) for the reconstruction of the second coordinate. These detectors will provide efficiency better than 95% per single plane at rate capability up to 15 kHz/cm$^2$, in presence of magnetic fields up to 0.3 T. Four different types of Micromegas quadruplets modules (SM1, SM2, LM1, LM2), built by different institutes, will compose the NSW.