  Small-diameter muon drift tube (sMDT) detectors have been developed for
upgrades of the ATLAS muon spectrometer. With a tube diameter of 15 mm, they
provide an about an order of magnitude higher rate capability than the present
ATLAS muon tracking detectors, the MDT chambers with 30 mm tube diameter. The
drift-tube design and the construction methods have been optimised for mass
production and allow for complex shapes required for maximising the acceptance.
A record sense wire positioning accuracy of 0.005 mm has been achieved with the
new design. 14 new sMDT chambers are already operational in ATLAS, further 16
are under construction for installation in the 2019-2020 LHC shutdown. For the
upgrade of the barrel muon spectrometer for High-Luminosity LHC, 96 sMDT
chambers will be contructed between 2020 and 2024.
