Precision drift tube chambers for the ATLAS detector at the Super-LHC

The measurement of muon momenta with high precision is a crucial aspect of the ATLAS experiment at the Large Hadron Collider (LHC) at CERN. The ATLAS muon spectrometer is equipped with three layers of Monitored Drift Tube (MDT) chambers in a toroidal magnetic field generated by superconducting air-core magnets, and is designed to withstand particle and background fluxes of up to 500 cm-2s-1. At the Super-LHC, the 10 fold luminosity upgrade of the LHC, the background rates are expected to increase by an order of magnitude. The possibility to improve the performances of the MDT chambers at high rates by reducing the diameter of the drift tubes from the current value of 30 mm to 15 mm has been investigated. We report on the design of muon chambers with 15 mm diameter drift tubes and on the results of cosmic ray measurements with a prototype detector in the presence of particle fluxes of up to 2000 cm-2s-1 at the Gamma Irradiation Facility at CERN