Neutronics Monte Carlo for the Burner
Quantifying the D-3He reaction's 5.44 percent neutron fraction so the burner's shielding and direct-conversion train are designed honestly.
Low-neutron, not aneutronic
The burner is a D-3He tandem-mirror generator. Its primary reaction is low-neutron but not aneutronic: a neutron fraction of 5.44 percent arises chiefly from D-D side reactions and their tritium products. Monte Carlo on L0 quantifies exactly where those neutrons go, because honest shielding and activation design depends on treating that 5.44 percent as real, not zero.
What the neutrons threaten
In the burner, neutrons are the component that most stresses structure and the direct-energy-conversion (DEC) train. The multi-modal DEC path, TWDEC, ultra-high-field MHD, and thermionics, sits in the particle exhaust and must be shielded from the neutron and activation environment. Monte Carlo maps the flux reaching each stage so materials and shielding are sized to the true load.
- D-D and secondary D-T neutron source characterization
- Neutron and gamma flux at the DEC train
- Activation of the 26.49 T plug and 17 T throat magnet regions
- Shielding optimization for the end cells and expander
Why this is subtle
Because the neutron fraction is small, naive analog Monte Carlo wastes effort tracking the dominant charged-particle physics that carries no neutrons. Kronos uses variance reduction to bias sampling toward the rare neutron-producing channels and the deep-shield regions where flux is low but consequential.
The tandem-mirror geometry is open-ended, not toroidal, so neutron streaming along the axis and out the end cells behaves very differently from the breeder's closed blanket. Monte Carlo captures this axial leakage directly, which matters for siting the DEC train and the expander in the neutron shadow.
Burner neutronics results feed the same downstream chain as the breeder: heating into thermomechanics, activation into waste and maintenance planning, and response tables into the twin. The difference is emphasis, the burner asks how to keep a small neutron flux from degrading a precise energy-conversion system, rather than how to maximize breeding.