Beta and Pressure Limits

Beta measures plasma pressure against magnetic pressure; the spherical tokamak's high-beta capability is what makes Hyperion compact and productive.

The efficiency of confinement

Beta is the ratio of plasma pressure to magnetic pressure. It measures how much plasma a given field can hold: high beta means a lot of fusion-producing pressure for the magnetic energy invested. Because fusion power density rises with pressure squared, achievable beta strongly determines how much power a machine of a given size and field can make.

The spherical-tokamak advantage

Low aspect ratio raises the beta limit. At aspect ratio 2.5 Hyperion can confine a higher relative pressure than a conventional tokamak at the same field, which is precisely why it produces 85.0 MW from a 1.2 m machine at about 8 T on axis. High beta is the physics payoff that justifies the demanding center-stack engineering of the ST line.

The limit and its consequences

Beta cannot be pushed without bound: above a stability limit the plasma develops pressure-driven instabilities that degrade confinement or end the discharge. Operating near the beta limit maximizes output but leaves less headroom against these modes, so the design targets an operating point that captures most of the beta benefit while staying stable. Where exactly that limit sits at Hyperion's shape and current is refined in stability modeling and tested at first-of-a-kind.

• Beta = plasma pressure / magnetic pressure
• Low aspect ratio raises the achievable beta
• Operating near, but safely below, the stability-set limit

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.