The Micromegas chambers for the ATLAS New Small Wheel upgrade

The ATLAS collaboration at LHC has chosenthe resistive Micromegas technology, along withthe small-strip Thin Gap Chambers (sTGC), for the high luminosity upgrade of the first muonstation in the high-rapidity region, the so called New Small Wheel (NSW) project. After theR&D, design and prototyping phase, the series production Micromegas quadruplets are beingconstructed at the involved construction sites in France, Germany, Italy, Russia and Greece.AtCERN, the final validation and the integration of the modules in Sectors are in progress.Theseare big steps forward for the installation of the first NSW, the NSW-A foreseen for the LHClong shutdown in 2020. The construction of the four types of large size quadruplets, all havingtrapezoidal shapes with surface areas between 2 and 3 m2, will be reviewed. The achievement ofthe requirements for these detectors revealed to be even more challenging than expected, whenscaling from the small prototypes to the large dimensions. We will describe the encounteredproblems, to a large extent common to other micro-pattern gaseous detectors, and the adoptedsolutions. Final quality assessment and validation results on the achieved mechanical precision,on the High-Voltage stability during operation with and without irradiation will be presentedtogether with the most relevant steps and results of the modules integration into sectors.