Study of the performance of the MicroMegas chambers for the ATLAS muon spectrometer upgrade.

MicroMegas (Micro MEsh Gaseous Structures) chambers and sTGC (small Thin Gap Chambers) have been chosen for the upgrade of the forward muon detectors of the ATLAS experiment to provide precision tracking and trigger capabilities. The MicroMegas chambers have been designed to allow operation in a high rate environment, to guarantee a resolution below 100 micron per point on a large area and to provide a fast trigger signal. In the last months several tests have been done on small area prototypes in order to verify that the requirements on resolution and rate capabilities are well matched. The results of the performance studies done on beams at CERN and of the ageing studies done at Saclay, are presented