The ITER magnet system: configuration and construction status

The magnet system is one of the critical core components of the ITER magnets, defining the machine capabilities to form and drive 15 MA 500 MW nuclear plasmas for hundreds of seconds. The magnets, the largest superconducting magnet system ever built with 50 GJ of stored energy, are technologically highly advanced components using large composite Nb3Sn 4-6 K force flow cooled conductors that, in order to maximise plasma performance and minimise cost, stretch current manufacturing technology to its limits. They work at the highest possible electrical (20-30 kV), mechanical (primary stresses up to 600 MPa) and superconducting performance consistent with very safe and very reliable operation over the life of the machine. The magnets, and the associated feeder system, are now entering the final manufacturing stages. Almost all prototyping and qualification work is completed, the sub-components such as the conductors are nearly fully manufactured (over 80% complete), some of the coil production lines are nearly fully 'loaded' and in several cases the 'first of a kind' final winding packs are nearing completion. In this article we review the main manufacturing difficulties that have been overcome, summarise the present production status of the magnets and describe the coming challenges of testing and assembly.