S76 is MetroVolt's integrated systems evaluation: one code, one frozen point, eight coupled constraints that must all pass at once. They do — and the margins are published, including the uncomfortable ones.
The eight gates at the Mode-D operating point: Greenwald density fraction (1.33 of limit 1.35), normalized β (4.96 vs 5.00 wall-stabilized — the binding constraint, +1%), safety factor (cylindrical q95 4.65 above its floor; equilibrium 5.24 by KX-8D), peak conductor field (24.42 < 26 T), magnet hoop stress (593 < 800 MPa), confinement requirement (H98 2.28 < 2.40), radial build (build-fit), and engineering gain (Q_eng 3.94 > 1). The Mode-C-era closure is retained as the labeled historical check.
The binding constraint — the one the design leans on hardest — is β/confinement physics, exactly matching the series' own risk statement: MetroVolt is 'a magnet-and-materials programme betting on a confinement result.' The systems code confirms the bet is the right one to interrogate.
Plenty of concepts pass their own chapters; far fewer pass a simultaneous closure test and then publish which wall they stand closest to. Knowing the binding constraint tells investors and researchers precisely which experiment de-risks the most value — that is what makes an honest systems code a capital-allocation tool, not just a physics exercise.
| Constraints evaluated | 8, coupled, simultaneous |
| Result at frozen point | all pass |
| Binding constraint | βN / confinement |
| Engineering gain Q_eng | 2.78 |
| Magnet stress margin | 604 MPa vs 900 yield (1.5×) |