The ITER superconducting magnet systems consist of 18 Toroidal Field (TF) coils, 6 Poloidal Field (PF) coils, a Central Solenoid (CS) coil, Correction Coils, and related structures. The lower PF coils are designed with redundant turns and a margin in current to avoid the need to replace them in case of local damage in one of the coil pancakes. Superconducting saddle-shaped correction coils placed around the machine outside the TF magnets are used to accommodate field errors due to manufacturing inaccuracies or to misalignments during assembly of the magnet coils, as well as to control resistive wall mode plasma instabilities. The magnets are combined in an integrated overall assembly which simplifies the equilibration of electromagnetic loads. When energised, the TF coils press together along their straight sections, forming a vault.  The coils are encased to aid their support and to transfer loads across keys between the cases.  The poloidal field crossing the TF coils creates overturning moments and circumferential torques on each TF coil.  A shell-like structure between the coils, to the extent port penetrations allow, permits these forces to be reacted within the magnet structure, and provides a strong support for the poloidal field coils.

All coils are cooled by a supercritical helium flow maintained by cryogenic circulation pumps.

The CS coil weighs about 840 t, and is about 12 m high and 4 m in diameter. It consists of a stack of 6 electrically-independent modules to allow good control of the inboard plasma shape. The stack is compressed to maintain its integrity under all operating conditions. The coil is wound in hexa- or double-pancakes, with all the joints in low field regions. This manufacturing process is being tested in the insert modules of the CS Model Coil Project (L-1).

Each TF coil weighs about 290 t, and is about 14 m high by 9 m wide. Its manufacturing process is being developed and tested in the TF Model Coil Project (L-2).

Both CS and TF coils use a similar superconductor configuration. The superconductor is a Nb₃Sn cable-in-conduit type. For the TF coils, some 1100 wires, about 0.7 mm in diameter, are twisted together inside a metal tube about 4 cm in diameter to form the conductor in lengths of 820 m. In use, supercritical helium flows inside the tube around the wires and down a central gap to cool them.

The superconducting Nb₃Sn compound is brittle, and initially the wires contain separated Nb and Sn (as well as a copper matrix) which react together after a 200 hour heat treatment at 650°C. This can only be performed after all cabling and conductor bending operations are complete, but before any temperature-sensitive coil components are added (such as the coil electrical insulation).

After the conductor has been wound into the shape required for the coil and heat-treated, it is electrically insulated with a wrap of glass fibre and kapton. Extra structural material is added outside the insulation and the glass-kapton is filled with liquid epoxy resin which is then cured. Conductor, insulation and structural reinforcement are bonded together to form pancakes and then a rigid winding pack. This winding pack is then further reinforced by putting it inside a steel housing.

Because of the brittleness of Nb₃Sn, its manufacture is a relatively expensive process. However, the PF coils occupy a field region where NbTi strand can be used, helping to keep their costs down. The PF coils are, however, geometrically linked with many systems, making their replacement difficult, so each coil is arranged with redundant turns so that "incipient" short circuits can be detected before they cause damage, and faulty double pancakes isolated. All coils can operate at their nominal current in this "backup" mode, although a lower cooling inlet temperature may be needed. As a further precaution, the coils can be rewound in situ or removed/replaced, although at a price in machine down-time.

Further details on the magnet design may be found in the Technical Basis.

The tokamak vessel and superconducting magnets are located inside a thermally shielded cryostat to maintain the cryogenic temperatures needed for superconductivity.

An animated view of the magnets and cryostat from outside illustrates the main features of the magnets.