Powering up ATLAS's mega magnet

Just before midnight on 9 November the largest superconducting magnet ever built was successfully powered up to the magnetic field of about 4 tesla. An electrical current of more than 21 000 amperes passed through the eight gigantic coils of the magnet.

This magnet is a main part of the ATLAS detector, one of the four big experiments on the Large Hadron Collider (LHC) due to be commissioned next year. The ATLAS Barrel Toroid magnet consists of eight superconducting coils, each in the shape of a round-cornered rectangle, 5 metres wide, 25 metres long and weighing 100 tonnes. It provides a powerful magnetic field for the ATLAS detector and will work with other magnets in the ATLAS experiment to bend the paths of charged particles in collisions.

During a six-week period in July-August, the ATLAS Barrel Toroid was cooled down to -269°C, just four degrees above the absolute zero, the temperature needed to create and maintain a superconducting state. Once the magnet reached full power, the current was gradually switched off and magnetic energy of 1.1 Gigajoules, the equivalent of about 10 000 car traveling at 70 km/h, has been safely dissipated, raising the magnet temperature to -218°C.

At 46 m long and 25 m high, ATLAS is the largest volume detector ever constructed for particle physics. Among the questions ATLAS will focus on are why particles have mass, what the unknown 96% of the Universe is made of, and why Nature prefers matter over antimatter. Some 1800 scientists from 165 universities and laboratories representing 35 countries are building the ATLAS detector and preparing to take data.

November 2006