ATLAS monitored drift tube chambers for super-LHC

After the high-luminosity upgrade of the Large Hadron Collider (LHC), the ATLAS muon spectrometer is expected to work at 10-fold background rates of gammas and neutrons. As the momentum resolution of the spectrometer is expected to be 10% a single tube resolution of the muon drift tubes of 80μm is required. At background rates around 1000 Hz/cm 2 space charge effects will lead in the slow and non-linear AR:CO2=93:7 gas mixture degrade the drift-tube spatial resolution. While this was studied for gammas and low energetic neutrons, almost no information exists for fast neutrons. This paper shows that: ·11 MeV neutrons at flux densities of 4 and 16 kHz/cm2 degrade the position resolution by only 10μm at a detection efficiency of 4x10-4. ·two modified inert gas mixtures selected by fastness and linearity of their position-drifttime ( r-t) relation show similar resolution as the standard gas in agreement with Garfield simulations. ·the resolution of newly developed 15 mm o drift tubes are mostly unaffected by space charge effects due to gamma irradiation up to 1400 Hz/cm2 according to Garfield simulations.