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The LHC at CERN plans to have a series of upgrades to increase its instantaneous luminosity up to 7.5 × 10 cm−2·s−1. The ATLAS experiment will upgrade its inner end-cap muon chambers to cope with the increased collision rate expected from the High-LuminosityLHC. This project, called New Small Wheel, includes resistive Micromegas chambers together with small-strip Thin Gap Chambers, forming a system of ∼2.4 million readout channels in total. This is the first time that Micromegas detectors are built in such a large scale. In total, 128 Micromegas modules up to 3 m in size, will be produced in different sites spread across Europe, targetting for an installation at the end of the Long Shutdown 2 of the LHC. One of the first series modules, equipped with a prototype of the final front-end electronics based on the VMM chip, was tested in a muon/pion beam at the H8 beam line of SPS at CERN during the summer of 2018. We present the test setup and performance results, namely efficiency and resolution, for perpendicular and inclined tracks. These studies were focused on determining the high voltage working point of the ATLAS Micromegas detectors. Studies with several gas mixtures were also carried out and will be presented. 1. The ATLAS NSW Upgrade In the context of the high luminosity upgrade of the Large Hadron Collider (HL-LHC) at CERN, its experiments also need to be upgraded to cope with the higher particle rates. One of the main upgrades of the ATLAS detector [1] is the replacement of the innermost end cap of the muon spectrometer by the New Small Wheel (NSW) [2]. Its position within the ATLAS detector is shown in figure 1a. The NSW will contribute to the trigger system of the ATLAS detector, reducing the muon fake trigger rate in the end cap region, which is currently responsible for 90 % of the bandwidth in that region. This will allow to maintain low trigger thresholds during the operation in the high rate environment of the HL-LHC. The second motivation for the NSW upgrade is to maintain a good spatial resolution and tracking efficiency at high rates, as these quantities deteriorate with higher rates at the current Small Wheel (SW). The NSW will use two detector technologies, namely the small-strip Thin Gap Chambers (sTGCs) and the Micro Mesh Gaseous Detectors (Micromegas, MM) [3], where the sTGCs mainly focus on the trigger and the MMs on the precise tracking. The NSW has a wheel like structure segmented into eight small and eight large sectors. Each sector consists of a sandwich like structure shown in 1b, where two MM wedges are surrounded by two sTGC wedges. Each wedge consists of two or three quadruplets for the MM and sTGCs respectively. As both sTGC and MM quadruplets each have 4 detector layers, the system has 16 detection layers in total. This offers a great

Test Beam Results and Performance Studies of ATLAS Micromegas Production Modules