If the 14.7 MeV fusion protons could be steered into the direct converter at full value, MetroVolt's output would jump. They cannot — not fully, not for free — and the series prices exactly how much of that dream survives contact with kinetics.
Fast protons born in D-³He fusion slow down on the plasma's electrons and ions before any extraction scheme can claim them. The deposited Fokker–Planck and exhaust analyses (S26, S51/S65, S72) bound the recoverable fraction: channeling 15–25% of the proton line redresses only 5–8% of the hot-ion sustainment tax — a ≤30% redress even at 100% channel efficiency.
That bound has teeth: it demoted hot-ion operation from baseline to adjudicated upside and set the near-thermal posture as the plant's operating baseline. The decision is enshrined as a gate (P6) with pre-registered criteria.
Every technology has a number its enthusiasts want to assume. Publishing the bound — and re-basing the whole plant on the posture that survives it — is why the rest of MetroVolt's ledger deserves belief. The upside remains real and gated: if channeling experiments beat the bound, the 0.84 GWe posture is already engineered.
| Channeling bound | ≤30% tax redress at 100% efficiency (S72) |
| Realistic credit | 15–25% of proton line ⇒ 5–8% of tax |
| Design consequence | near-thermal = baseline; hot-ion = P6-gated upside |
| Gate | P6, pre-registered criteria |
| Analyses | S26 · S51 · S65 · S72, deposited |