Hold out your hand and in one minute hundreds of muons will have passed through your palm. Muons are one of the high-energy cosmic ray particles that can pass through most solid structures – even the ATLAS detector’s calorimeter, which is designed to absorb particles and measure their energy. A specific system is required to measure muons. Until now, the ATLAS muon system was almost completed, but not quite. The last of the 62 chambers in the Extended Endcap (EE) region was installed just before summer this year.

This Tuesday, if all goes according to plan, will mark the end of a very long journey for many High Energy Physicists. The first 7 TeV Collisions will signal the end of the the commissioning period of the LHC and its experiments.

Celebrations are underway in the ATLAS Experiment, as the final element of the detector was lowered into the cavern on Friday February 29th, 2008. The second “small wheel” is also the final part of the muon subsystem, but the wheels themselves are small in name only. At 9.3 metres in diameter, and weighing in at 100 tons each, moving them from their construction warehouse, at the north-west tip of the CERN site in Geneva, to the underground ATLAS cavern was a challenge which was anything but small.

It could be a scene from a James Bond movie. But this action shot of two intrepid rappellers (abseilers) was in fact taken in the ATLAS experimental cavern one night in December. François Butin, the ATLAS experimental area manager, tells the story behind the photograph.

The cables within the ATLAS detector may be thought of as the blood vessels and nervous system of the experiment; they carry power to the detector, they deliver messages to control its functions and they relay the data taken, ready for analysis. Just as blood vessels and nerves criss–cross and connect the organs and tissues of the human body, cables penetrate the whole of the ATLAS volume, reaching each and every one of its elements.

The magnets on either end of the ATLAS detector (called end–cap toroid magnets) dominated November’s work in the experimental cavern. The ATLAS magnet team took a significant step towards finishing work on the ATLAS detector as testing of the magnets began.

Leading up to the lowering of the pixel detector into the ATLAS cavern, final preparations were proceeding quickly.

On 13 June 2007 the first of two giant toroid magnet end-caps was lowered into the ATLAS cavern on the A side. This complex and spectacular operation was completely successful.

Data have recently been collected with the toroidal magnetic field will provide for the first time the measurement of the cosmic ray muons' momenta in the ATLAS experiment and allow studies on trigger optimization, chamber calibration, chamber alignment and magnetic field maps. More than one million events were acquired. They are now being analyzed by enthusiastic members of the collaboration.

The ATLAS Detector safety system (DSS) has the mandate to put the detector in a safe state in case an abnormal situation arises which could be potentially dangerous for the detector. It covers the CERN alarm severity levels 1 and 2, which address serious risks for the equipment.