It is tempting to push the burner toward zero neutrons by loading it with helium-3, but on the locked config that breaks closure. Above a helium-3 fraction of about 0.43 the power balance no longer closes: the helium-3-heavy fuel does not react hard enough to fund the mirror's end losses. True near-aneutronic operation is a named future machine, not this design.
On the locked closing config the window is x_He3 in [0.20, ~0.43]. Below 0.20 the charged-power budget starves; above ~0.43 the reaction rate falls too far and the machine no longer closes. Reaching near-aneutronic cleanliness (x ≥ 0.45) would require a redesigned machine — higher field, density, or size — not just more fuel.
The honest version of the aneutronic dream names its cost. Helium-3-helium-3 fusion is a north star worth stating, but presenting it as a tweak to this machine would be false. The record keeps it as a labeled future option, which is what lets the low-neutron claim on the actual design stay credible.
| Closure window | x_He3 in [0.20, ~0.43] |
| Below 0.20 | charged-power budget starves |
| Above ~0.43 | reaction rate too low; does not close |
| Near-aneutronic (x >= 0.45) | requires a REDESIGNED machine |
| 3He-3He | a north star, not this design |