The Spherical-Tokamak Advantage

A low aspect ratio packs the plasma close to the center column, raising achievable plasma pressure per unit magnetic field — the reason Hyperion is compact.

A tokamak squeezed toward a sphere

A conventional tokamak is a fat doughnut; a spherical tokamak (ST) pushes the aspect ratio down until the plasma hugs the central column, making the plasma cross-section look almost spherical with a narrow hole through the middle. Hyperion runs at aspect ratio A 2.5 with major radius R0 1.2 m — a genuinely compact machine.

The physics payoff is high beta: the ratio of plasma pressure to magnetic pressure that an ST can sustain is markedly higher than in a conventional tokamak of the same field. Higher achievable beta means more fusion power for a given magnet, which is what lets a machine this small reach 85.0 MW.

What the geometry costs

The tight geometry concentrates everything onto a slender center post: the toroidal-field conductors, the neutron flux, and the heat. There is little room for shielding on the inboard side, so the center post takes damage and has a limited lifetime (noted at ~0.01 fpy). The ST advantage is real, but it is paid for at the center column. The design's posture is to accept that bargain openly: the spherical geometry is chosen because it makes a compact, high-beta breeder possible at all, and the center-post penalty is treated as a managed, replaceable cost rather than a reason to abandon the configuration.

• Aspect ratio A 2.5, R0 1.2 m — compact by design
• Higher achievable beta than a conventional tokamak of equal field
• Cost: a highly stressed, life-limited center post

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.