September saw the completion in the underground cavern of the first of the big wheels for the ATLAS muon spectrometer. The muon spectrometer includes four large wheels at each end of the barrel part of the detector, each measuring 25 m across. Six of these wheels will be composed of thin-gap chambers for the muon trigger system – the first wheel is one of these – while the other two will be made of monitored drift tubes to measure the position of the muons.
