A gas monitor for the ATLAS Muon Spectrometer precision chambers

The ATLAS Muon Spectrometer incorporates some 354,000 drift tubes assembled into 1200 monitored drift tube (MDT) precision chambers, with a total gas volume of 723,000 dm
³
. A gas mixture of 93% Ar and 7% CO
₂
at 3 bar flows in a parallel feed at a rate of one chamber volume per day. Achieving the 80 mum single drift tube design resolution requires stringent gas quality control. We report on the design and initial performance of a dedicated MDT mini-chamber conceived for continuous monitoring of the ATLAS Muon Spectrometer MDT system operating gas. This chamber enables measurement of the drift spectra from which gas properties relevent to MDT calibrations are determined.