Performance of large area micromegas detectors for the ATLAS muon spectrometer upgrade project

32 high-rate capable SM2 Micromegas quadruplets are built, for the upgrade of the Small Wheels of the ATLAS muon spectrometer. The cathodes and strip-anodes of the 2 m
²
quadruplets consist of stable honeycomb sandwiches with a requested planarity better than 80 μm. The qualification of full-size SM2 quadruplets will be performed in the Munich Cosmic Ray Measurement Facility (CRF). Two fully working 4 m × 2.2 m ATLAS drift-tube chambers provide muon tracking, a RD51 SRS based data acquisition system provides readout of all 12288 electronic channels using 96 APV25 front-end boards. The goal is to measure the homogeneity of pulse-height and efficiency and to determine the planarity of the sandwich planes and the positions of the readout-strips. This has been pioneered by studying a 102 × 92 cm
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Micromegas chamber with similar readout pitch in the CRF using the TPC-like analysis method. At trigger rates above 100 Hz data taking takes only a few days for sufficient statistics. Shifts of readout planes and bulging due to overpressure were resolved with an accuracy better than 50 μm, single plane angular resolution with an accuracy of about 5° and spatial resolution of 300 μm in agreement with 83 μm for the same detector at high energy 120 GeV pion beams when taking into account the multiple scattering of the low energy cosmic muons.