Deep Dive: The Radial Build & Center Stack

Everything must fit across the machine's radius — plasma, wall, vessel, shield, and magnet. The crowded center stack is where a low-neutron design earns its space.

Radial build

Plasma → wall → vessel → shield → magnet

Peak-field radius

R_c = 1.40 m

Constraint

Inboard space is tight (low aspect ratio)

Consistency

Radial-build analysis S06

The radial build is the cross-sectional stack-up of everything from the plasma center outward — plasma, first wall, vacuum vessel, neutron shield, and magnet — and it must all fit, especially on the crowded inboard side. In a spherical tokamak, the center stack has the least room and the most to accommodate.

Kronos MetroVolt's inboard magnet leg reaches peak field at R_c = 1.40 m, and the shield must sit between it and the plasma in minimal radial space. The deposited radial-build consistency check (S06) confirms the layers fit self-consistently.

This packaging problem is the crux of the compact spherical approach — and precisely where being low-neutron is decisive: a thinner shield suffices, so more of the scarce inboard radius goes to conductor, enabling the 24.6 T field. Every millimetre is contested. See high vs low aspect ratio.