Roll out the Barrel

The largest superconducting magnet ever built has successfully been powered up to its operating conditions at the first attempt.

Called the Barrel Toroid because of its shape, the magnet is a vital part of ATLAS, one of the major particle detectors being prepared to take data at CERN’s Large Hadron Collider (LHC), the particle accelerator due for activation next November.

ATLAS will help scientists probe the big questions of the Universe: what happened moments after the Big Bang? Why does the material in the Universe behave the way it does? What is its unknown 96 per cent made of?

Measuring 46m long x 25m wide x 25m high, the Barrel (pictured below) consists of eight round-cornered, rectangle-shaped super-conducting coils, each 5m wide x 25m long and weighing 100 tonnes, and aligned to millimetre precision. It will work together with other magnets in ATLAS to bend the paths of charged particles produced in collisions at the LHC, enabling important properties to be measured.

The Barrel was first cooled down over a six-week period between July-August to reach -269º C. It was then powered up step-by-step to higher and higher currents, reaching 21,000A for the first time during the night of 9 November. This is 500A above the current needed to produce the nominal magnetic field. Afterwards, the current was switched off and the stored magnetic energy of 1.1 GJ, the equivalent of about 10,000 cars travelling at 43mph (70kph) has now been safely dissipated, raising the cold mass of the magnet to -218ºC.

The Barrel is financed by the ATLAS Collaboration and has been built through co-operation with France’s CEA-DAPNIA laboratory, Italy’s INFN-LASA laboratory and CERN.