Performance of Large Area Micromegas Detectors for the ATLAS Muon Spectrometer Upgrade Project

Four German institutes are building the 32 high-rate capable SM2 Micromegas quadruplets, for the upgrade of the Small Wheels of the ATLAS muon spectrometer. The cathodes and strip-anodes of the m$^2$ in size quadruplets consist of stable honeycomb sandwiches with a requested planarity better than 80 $\mu$m. The qualification of a full-size SM2 quadruplet, foreseen by ATLAS time schedule for August 2015, will be performed in the Munich Cosmic Ray Measurement Facility (CRMF). Two fully working 4 m$\times$ 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 frontend boards. We report on homogeneity of pulse-height and efficiency and will present measurements of the planarity of the sandwich planes and the positions of the readout-strips. This has been pioneered by studying a $102 \times 92$ cm$^2$ Micromegas chamber with similar readout pitch in the CRMF 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 buldging due to overpressure were resolved with an accuracy better 50 $\mu$m, single plane angular resolution with an accuracy of about 5 $^\circ$ and spatial resolution of 300 $\mu$m in agreement with 83 $\mu$m for the same detector at high energy 120 GeV pion beams taking into account the multiple scattering of the 2 GeV cosmic muons.