Neutronics and Shielding Design
Shielding protects magnets, structure, and people from neutrons and the radiation they create, and its design is a computational optimization.
What shielding must do
Neutrons and secondary gamma rays must be attenuated to protect superconducting magnets from dose, keep structural activation manageable, and limit heating where it is unwanted. Shielding does this with layered materials chosen for their scattering, absorption, and heat-handling properties.
The trade-offs
- More shielding protects better but takes space and adds mass.
- Space near the plasma is scarce, especially in a compact spherical tokamak.
- Some materials moderate neutrons well but activate badly, or vice versa.
Why it is a search
Shielding design is an optimization over material choice, layer thickness, and geometry, evaluated with neutron transport. Each candidate is scored on magnet dose, activation, and heating, and the best trade-offs are found by sweeping many layouts rather than hand-tuning one.
The Hyperion challenge
The Hyperion breeder is a spherical tokamak, so the central column is tight on space while carrying high field, up to 16.84 T peak. Protecting the inboard magnets there without stealing room from the plasma is one of the harder shielding problems, and it is solved by computation, not intuition.
Coupling to breeding
Shielding and the breeding blanket compete for the same neutrons and the same space, so shielding is optimized jointly with tritium breeding to keep the breeding ratio at 1.8 while still protecting the magnets.
Honest margins
Nuclear data uncertainty means dose predictions carry error bars, carried through uncertainty-driven design so the shield is sized for the credible worst case, not the nominal one.