Magnets

The superconducting coil system consists of 18 NbTi toroidal field (TF) coils; a Nb3Sn central solenoid (CS) made from 4 coil modules; 6 NbTi equilibrium field (EF) coils; common components, such as coil feeders and current leads. The D-shaped TF coils are wound from a square steel-jacketed NbTi cable-in-conduit conductor force-flow-cooled by supercritical (~4K) helium. The winding pack is inserted in a stainless steel casing with additional cooling channels to aid magnet cool-down.

The TF coils are wedged together over their straight section to support centralising forces.  Overturning moments on the coils are supported by keys between the casing in the upper and lower inboard curved regions.  There is an outer intercoil structure in the region between the vessel ports. This consists of bolted shear plates with friction and insulated surfaces contacting the TF coil case. 

The TF coil casing includes a gravity support composed of struts which are bolted to the cryostat base.  

The CS uses a conductor similar to that used for ITER and using identical strand as for the ITER TF conductor.  The conductor is a circular Nb₃Sn cable in square conduit cooled by supercritical helium.  The four independent modules can be powerd independently.

All structural and operational loads are reacted internally.  The CS is supported from the bottom of the TF coil casing..

The EF coils conductor is a circular NbTi cable in square conduit cooled by supercritical helium.  The coils are clamped to the TF coil case. They are self-supporting with respect to radial (in-plane) loads.

All the coils use high temperature (~50K) superconductor current leads to connect to the power supplies.

There are other (normal conducting) magnet coils used inside the vessel to control plasma instabilities and to compensate for inevitable manufacturing and assembly errors in the superconducting magnets. These are part of the in-vessel components.