Why STs Reach High Beta
The tight, low-aspect-ratio geometry of a spherical tokamak stabilizes pressure-driven modes, lifting the achievable beta above conventional tokamaks.
Geometry that likes pressure
In a spherical tokamak, field lines spend a large fraction of their length on the outboard, low-field side where the field's curvature is favorable, and the strong field-line pitch near the center column improves stability. The net effect is that pressure-driven instabilities set in at higher beta than they would in a conventional tokamak of equal field.
This is the core of the ST value proposition and the reason Hyperion can be compact. A higher beta ceiling means the same magnet holds more fusion-producing pressure, so a small machine at 8 T on-axis can reach 85.0 MW. Without the elevated beta limit, a device this size would fall well short of its power target.
Not a free lunch
The same geometry that lifts beta forces everything onto a slender center post with little inboard shielding, drives high heat flux to a compact divertor, and demands strong shaping that is vertically unstable. The high-beta advantage is genuine, but it is bought with a concentrated set of engineering stresses that the rest of the physics section keeps in view.
- Favorable field-line geometry raises the pressure-instability threshold
- Higher beta → more fusion power per unit field → compact machine
- Bought with center-post stress, high heat flux, and vertical instability
This page describes a design-and-simulation study, not a built machine. Construction begins Q2 2027; first-of-a-kind first tritium is targeted near 2030. No hardware net-gain is claimed before FOAK.