Recent and ongoing ageing studies for the Atlas muon spectrometer drift tubes

Abstract The Atlas muon spectrometer relies on Monitored Drift Tubes (MDTs) for track reconstruction in most regions. Expected count rates due to photons reach up to 1500 Hz/cm for the innermost MDTs. For a gas gain of 2 × 10 4 , this corresponds to an overall accumulated charge of up to 0.6 C/cm, which the MDTs must be able to withstand in 10 years of LHC operation without a degradation in their performance. With the main MDT parameters and the design frozen and chamber production well under way, the focus of present ageing studies is on testing final Atlas chambers instead of using small, dedicated setups under very well-controlled conditions as in the past. This paper summarizes the results of such a study performed at the CERN Gamma Irradiation Facility GIF under realistic Atlas conditions. One of the main goals was to evaluate for the first time the principle of gas recirculation and a prototype of the Atlas circulation system. The paper also reviews ongoing measurements at CERN and in Freiburg.