MetroVolt drives 43.0 MA of plasma current, among the largest ever specified. What keeps that ambition honest is a self-imposed floor: the edge safety factor q95 stays at or above 5, verified by free-boundary equilibrium, not estimated from formulas.
The safety factor counts how many times a field line winds the long way around for each short-way turn; low q95 invites the kink instabilities and disruptions that end discharges violently. Formula estimates flatter shaped plasmas, so MetroVolt computes q95 from the actual FreeGS equilibrium at δ = −0.30: q95(eq) = 5.24 at the operating 43 MA and 6.37 T (KX-8D) — the ≥5.0 floor met at full current (the 6.0 T-era benchmark gave 4.94 and had forced a trim to 42.5 MA).
The robustness study (S79) then asks the impolite question: what if current falls short? Answer, published: a 10% Ip shortfall is not recoverable by density trim — plasma current is the least forgiving parameter in the design. That finding shapes the control philosophy and the disruption engineering budget.
A disruption at 43.0 MA stores real energy (11.5 GJ; ~630 MN vertical load, KX-24D — quantified in the deposit), so the q95 discipline is the difference between a power plant and a research risk. Buyers of firm power are really buying operating margin; ours is computed, floored, and stress-tested against its own worst parameter.
| Plasma current Ip | 43.0 MA |
| Safety-factor floor | q95(eq) ≥ 5.0 — met at full current |
| Operating solve | q95(eq) 5.24 at 43 MA, 6.37 T (KX-8D) |
| Least forgiving parameter | Ip (S79, adverse, published) |
| Disruption ledger | 11.5 GJ · ~630 MN (KX-24D; mitigated by SPI) |