ATLAS: Full power for the toroid magnet

The 9th of November was a memorable day for ATLAS. Just before midnight, the gigantic Barrel toroid magnet reached its nominal field of 4 teslas in the coil windings, with an electrical current of 21000 amperes (21 kA) passing through the eight superconducting coils (as seen on the graph). This achievement was obtained after several weeks of commissioning.

The ATLAS Barrel Toroid was first cooled down for about six weeks in July-August to -269°C (4.8 K) and then powered up step-by-step in successive test sessions to 21 kA. This is 0.5 kA above the current required to produce the nominal magnetic field. Afterwards, the current was safely switched off and the stored magnetic energy of 1.1 gigajoules was dissipated in the cold mass, raising its temperature to a safe -218°C (55 K).

'We can now say that the ATLAS Barrel Toroid is ready for physics,' said Herman ten Kate, project leader for the ATLAS magnet system.

The ATLAS barrel toroid magnet is the result of a close collaboration between the magnet laboratories CEA-Saclay, INFN-LASA and CERN. Components have been contributed 'in-kind' by the funding agencies through their national industries in France (CEA), Italy, Germany (BMBF), Spain, Sweden, Switzerland, Russia, and through JINR Dubna. Final integration and testing of the coils at CERN as well as assembly of the toroid in the ATLAS underground cavern was achieved in collaboration, with JINR providing most of the manpower and heavy tooling.