Power Balance & the Lawson Criterion
Net gain requires fusion power to exceed radiation, transport, and injection losses; for D–He-3 this triple-product bar is much higher than D–T.
The balance that must close
A power-producing plasma must generate more fusion energy than it loses. The bookkeeping compares fusion power against three drains: radiation (bremsstrahlung and synchrotron), transport (particles and heat leaving confinement), and the input power needed to sustain heating and plugging. Net gain requires the sum on the loss side to stay below the fusion source.
The Lawson criterion expresses this as a triple product of density, temperature, and confinement time (n T τ). For D–3He the required triple product is roughly an order of magnitude higher than D–T, because the reactivity is lower and the radiation losses are higher. That raises the bar on every confinement parameter at once.
Why this frames the gates
The confinement time and plug potential needed to close this balance for D–3He are what push the plug into an operating regime beyond any built device, and what make the coil stresses so demanding. The power balance is the physics behind the honest gates — it is achievable on paper and unproven in hardware.
It is worth being precise about what the triple product does and does not promise: satisfying n T τ is necessary for net gain but not sufficient, because it says nothing about whether the required τ can actually be held, or whether the plug that holds it can be built. The burner's gates are exactly the places where the paper triple product and the buildable machine diverge.
- Fusion power > radiation + transport + injection
- D–3He triple product ~10× D–T
- Higher n, T, and τ all required at once
- Drives the plug-stress and plug-regime gates