Geometrical precision alignment of the Micromegas detectors for the 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 design luminosity (10^{34} cm^{−2}s^{−1}). To meet the requirements of higher rates environment of HL-LHC era, the muon system of ATLAS detector needs to be upgraded. Therefore, the present small wheel will be replaced by the New Small Wheel (NSW), which will be constituted by MicroMegas micro-pattern gaseous detectors and small-strip Thin Gap Chambers. The meth- ods adopted to achieve the challenging required geometrical precision of Micromegas chambers are presented. Specific measurement devices have been developed in the last few years to deter- mine the mechanical metrology quality of Micromegas chambers, required for NSW. Planarity measurements of panels as well as modules after assembly are done with a specifically developed co-ordinate measuring machine. The methodology and the results will be presented. Results of in-plane measurements performed using Rasnik masks etched on the PCBs are also reported.