MetroVolt's torus is nearly a sphere with a hole through it: major radius 5.75 m, minor radius 2.875 m, aspect ratio exactly 2.0. Compactness here is not styling — it is physics leverage.
Plasma pressure scales with the square of the field, but what a magnet buys you depends on geometry: low-aspect-ratio machines reach higher normalized pressure (β) per unit field. MetroVolt runs a toroidal β of 11.6% and a normalized βN of 4.96 at the frozen Mode-D point (wall-stabilized against the computed 5.0 limit) — numbers a conventional aspect-ratio-3 machine cannot hold at the same safety margins.
Elongation κ = 2.56 stretches the plasma vertically, adding cross-section (2,402 m³ of plasma volume) and bootstrap current. The equilibrium, vertical stability, and the 0.42 m of spare radial build are all computed and deposited — the compactness closes as a system (S76), not as a slogan.
Machine volume drives capital cost. At R₀ = 5.75 m, MetroVolt's vacuum vessel, magnets, and shield fit a build envelope that existing heavy industry can fabricate and existing sites can host, while still delivering gigawatt-class fusion power. The spherical-tokamak bet is that the shortest path to commercial fusion economics runs through a smaller, higher-β machine — and MetroVolt writes that bet down in checkable numbers.
| Aspect ratio A | 2.0 (R₀ 5.75 m / a 2.875 m) |
| Elongation κ | 2.56 |
| Toroidal β | 11.6% |
| Normalized βN | 4.96 (wall-stabilized; computed limit 5.0) |
| Plasma volume | 2,402 m³ |
| Spare radial build | 0.42 m |