Neutron Fraction and Fuel Choice
The 5.44% neutron fraction is the honest cost of running D–3He in a real plasma, and it shapes shielding, materials, and maintenance.
Low, but not zero
Marketing a fusion fuel as aneutronic invites the assumption that it produces no neutrons. That is not true for D–3He in a real device, and Aegis does not claim it. The design point carries a neutron fraction of 5.44% of total fusion power — a large reduction from D–T's roughly 80%, but a real number that the machine is engineered around. Being honest about it is what lets the shielding and materials be sized correctly.
What 5.44% buys and costs
The low fraction is why Aegis suits fixed installations: less neutron flux means less activation of structures, lighter shielding than a D–T machine of similar output, longer component life, and a smaller waste and maintenance burden. But 5.44% is not nothing. It still requires neutron shielding, activation-aware material choices, and a maintenance plan. The design treats the neutron fraction as a real engineering input rather than rounding it to zero.
- 5.44% vs ~80% for D–T — a large but incomplete reduction
- Enables lighter shielding and longer component life
- Still requires shielding and activation-aware materials
- Sized from the honest number, not an idealized claim
The fuel choice and the neutron fraction are inseparable. Choosing D–3He is choosing a machine whose whole shielding, materials, and maintenance philosophy follows from 5.44% — and choosing to plan a helium-3 supply to feed it.