The Center Stack

The center stack is the crowded central column of a spherical tokamak, holding the inboard magnet and shield in minimal space — a low-neutron design's advantage.

What

The central column of a spherical tokamak

Contains

Inboard TF legs + neutron shield

Constraint

Very little radial space

Kronos edge

Low-neutron → thinner shield fits

The center stack is the central column running up the middle of a spherical tokamak. Because low aspect ratio squeezes the hole in the middle, the center stack is the most space-constrained region of the machine — and it has to accommodate both the inboard TF coil legs at peak field and the neutron shield that protects them.

That real-estate squeeze is the defining engineering tension of the spherical approach: every millimetre of shield competes with every millimetre of conductor. This is exactly where the Kronos low-neutron fuel choice earns its keep — fewer neutrons mean a thinner shield suffices, freeing space for the magnet. The design carries an explicit neutron-fluence budget for the shielded center stack.