Neutronics Twin
A neutronics twin tracks the fusion neutron field and its effects: heating, breeding, activation, and material damage throughout the machine.
Following the neutrons
Fusion neutrons carry a large share of the energy and pass through matter, depositing heat, breeding tritium, activating materials, and damaging structures. A neutronics twin tracks where these neutrons go and what they do, providing the fields that drive heating, tritium breeding, and component life throughout the machine. It couples the plasma source to nearly every structural and materials concern.
What the neutron field drives
- Volumetric heating deposited in the blanket and structures
- Tritium production through neutron capture in lithium
- Activation of materials, creating radioactive isotopes
- Displacement damage that changes material properties over time
The computational challenge
Neutron transport is expensive to compute accurately, traditionally by Monte Carlo methods that trace many particle histories. This is far too slow for a real-time twin, so the neutronics twin relies on precomputed response functions and surrogates: relate the plasma neutron source, which the plasma twin estimates, to the fields elsewhere through fast mappings validated against full transport calculations. See surrogate models.
Coupling to other twins
The neutronics twin is a hub. It takes the neutron source strength and distribution from the plasma state estimate, and it feeds heating into the thermal twin, tritium production into the breeding-cycle twin, and damage rates into the life-tracking twin. Getting this coupling right is what makes the plant twin coherent rather than a set of disconnected models.
In the Kronos machines
The two machines differ sharply in their neutron environment. The Hyperion breeder, burning deuterium and tritium, produces intense 14 million-electron-volt neutrons that drive its tritium breeding, designed to a breeding ratio of 1.8, and dominate its material damage. The burner, burning deuterium and helium-3, has a neutron fraction of only 5.44 percent, so its neutronics twin carries a much smaller load. Both are built on validated neutron-transport models today, with real activation and damage data available only after the machines operate. See tritium breeding cycle twin and thermal-hydraulic twin.