For MetroVolt to close, its plasma must hold energy 1.8 to 2.2 times better than the standard H-mode scaling law (IPB98(y,2)) predicts for its size and field — depending on operating mode. That multiplier, H98, is the design's single most important open question, and we treat it that way.
The requirement is mode-dependent and every value is published: 1.84 at the frozen hot-ion point on the profile basis, 1.91 at the 80:20 mix, up to ≈2.2 for the near-thermal operating baseline (the 0-D systems gate returns 2.24 at the deposited Ti = Te = 42 keV reference; the documented convention offset reconciles it to ≈2.2 on the profile basis).
Why is it plausible? Negative-triangularity experiments already report confinement at or above H-mode-like levels without ELMs, and MetroVolt's high-β, high-density spherical geometry is the regime where NT core turbulence behaves best. The claim is extrapolated, gated, and assigned to a decision gate (S18) with deposited gyrokinetic decks waiting on HPC time.
Every fusion venture is betting on something. We name our bet, price it, and publish the experiment that settles it. If NT confinement lands where the evidence points, MetroVolt closes with margin; the requirement band, the fallback posture, and the adverse cases are all in the open record.
| Required H98 band | ≈1.8–2.2 (mode-dependent, profile basis) |
| Frozen hot-ion point | 1.84 |
| Near-thermal baseline | ≈2.2 (0-D gate 2.24 @ 42 keV) |
| Adjudicating gate | S18 (nonlinear gyrokinetics) |
| Evidence base | DIII-D / TCV NT experiments |