The Micromegas Detectors for ATLAS New Small Wheel Upgrade

The upgrade of the Large Hadron Collider (LHC) to the High Luminosity LHC (HL-LHC) is required to probe the physics beyond Standard Model. After the ongoing long shutdown (LS2) and eventually after LS3 in 2026, the accelerator luminosity will be increased up to 7 times as compared to designed luminosity value, thus reaching 7 $\times $ 10$^{34}$ cm$^{-2}$s$^{-1}$. To meet the requirements of HL-LHC era, the muon system of ATLAS detector needs to be upgraded. Therefore, the existing forward inner part of ATLAS muon spectrometer, the small wheel comprised of Cathode Strip Chambers (CSC), monitored Drift Tubes (MDT) chambers, and Thin Gap Chambers (TGC) will be replaced by the New Small Wheel (NSW). The NSW will be constituted by MicroMegas gaseous detectors (from the MPGD family) and small-strip Thin Gap Chambers (sTGC). Micromegas detectors will be used mainly for tracking and sTGC detectors mainly for triggering purpose. But each type of detector is able to participate in both systems. Micromegas are ionization-based gaseous detectors made up of parallel plates, having a thin amplification region separated from the conversion region via a thin metallic mesh. For each of the two NSW, 4 Micromegas detectors will be installed in each of the 16 sectors. Four types of Micromegas termed as SM1, SM2, LM1, and LM2 will be installed, each detector with an individual area between 2 and 3 m$^{2}$. At CERN, integration of these detectors is in progress. In this talk, the construction of Micromegas detectors, the methodology to obtain the required and challenging results as well as obtained results will be presented. Specific measurement devices have been developed in the last few years to determine the mechanical metrology quality of Micromegas chambers, also presented here. The validation results using cosmic muons will also be shown.