Helium-3 as a Fusion Fuel
Helium-3 is itself a candidate fusion fuel, most practically burned with deuterium, offering reactions that release much of their energy in charged particles.
Fuel as well as coolant
Helium-3 is best known in this library as a cryogenic working fluid, but it is also a fusion fuel. Two reactions involve it: deuterium with helium-3, producing a proton and a helium-4 nucleus, and helium-3 with helium-3, producing helium-4 and two protons. Both are of interest because their primary energy release is carried by charged particles rather than neutrons.
The charged-particle advantage
In a deuterium-tritium reaction, most of the energy comes out as fast neutrons, which cannot be steered by fields and which activate surrounding materials. In the deuterium-helium-3 reaction the main products are charged, which in principle allows direct conversion of their energy to electricity and reduces neutron-induced activation. This is the appeal of helium-3-based fuel cycles for certain reactor concepts.
Why it is difficult
Helium-3 fuels require much higher temperatures than deuterium-tritium to reach useful reaction rates, because the higher nuclear charge raises the Coulomb barrier the nuclei must overcome. A pure deuterium-helium-3 plasma also contains deuterium-deuterium side reactions that still produce some neutrons. These challenges mean helium-3 fusion is more demanding than deuterium-tritium, even setting aside the scarcity of the fuel itself.
The Kronos context
Kronos frames its burner machine as a deuterium-helium-3 tandem-mirror generator with a reported neutron fraction of 5.44 percent, using direct energy conversion, in housings named Aegis for fixed defense sites and MetroVolt for data centers. These are design and simulation studies; a test burner is planned for 2032 with commercial fleets projected for 2036, and no hardware net-gain claim is made before the breeder's first-of-a-kind milestone. The point here is conceptual: helium-3 is both what keeps qubits cold and, in a different arena, a fuel whose low neutron output is its attraction.
- Deuterium-helium-3 yields a proton and helium-4
- Energy released mostly in charged particles allows direct conversion
- Requires higher temperature than deuterium-tritium
- Kronos burner is a D-helium-3 design study, not built hardware