Toroidal Field Coils

The toroidal field coils produce the main confining field. In a spherical tokamak their inboard legs crowd the center stack at peak field.

Job

Produce the main toroidal magnetic field

Peak field location

Inboard legs, on the center stack

Kronos peak

24.6 T on the inboard conductor

Material

Graded REBCO winding pack

The toroidal field (TF) coils are the D-shaped magnets that wrap the plasma the "long way" around, producing the dominant magnetic field that confines it. The field is strongest on their inboard legs — closest to the machine's central axis — which is where a magnet is most stressed and where the peak conductor field is quoted.

In a spherical tokamak like Kronos MetroVolt, those inboard legs are packed into the crowded center stack, and they carry the design's 24.6 T peak field using a graded REBCO winding pack. Getting a very high field through very little radial space is the central magnet challenge of the compact high-field approach — and the reason the low-neutron fuel, with its thinner shield, helps so much.