Construction and test of the MicroMegas chambers for the upgrade of the ATLAS Muon Spectrometer

MicroMegas (MM, MICRO MEsh GASeous structure chambers) are Micro-Pattern Gaseous Detectors, designed to provide a high spatial resolution, efficiency better than 95% per single plane, in a highly irradiated enviroment. MM chambers have been chosen as precision tracking detectors for the upgrade of the forward muon spectrometer of the ATLAS experiment (ATLAS Collaboration, JINST, 3 (2008) S08003) composing the New Small Wheel (NSW). MM modules are composed by 4 read-out layers, two used for the reconstruction of the precision coordinate and two inclined by ±1.5° for the reconstruction of the second one. The National Institute of Nuclear Physics (INFN) is deeply involved in the construction of these chambers and in their validation. Preliminary results on the INFN SM1 prototypes are presented.