  With half the drift-tube diameter of the Monitored Drift Tube (MDT) chambers
of the ATLAS muon spectrometer and otherwise unchanged operating parameters,
small-diameter Muon Drift Tube (sMDT) chambers provide an order of magnitude
higher rate capability and can be installed in detector regions where MDT
chambers do not fit. The chamber assembly time has been reduced by a factor of
seven to one working day and the sense wire positioning accuracy improved by a
factor of two to better than ten microns. Two sMDT chambers have been installed
in ATLAS in 2014 to improve the momentum resolution in the barrel part of the
spectrometer. The construction of an additional twelve chambers covering the
feet regions of the ATLAS detector has started. It will be followed by the
replacement of the MDT chambers at the ends of the barrel inner layer by sMDTs
improving the Performance at the high expected background rates and providing
space for additional RPC trigger chambers.
