Coupling Multi-Physics Models
A plant twin is a federation of coupled physics models that must exchange boundary information consistently without instability.
One machine, many physics
No single code captures a fusion plant. The plasma, magnets, neutron field, coolant, and structure each have their own physics and their own solver, yet they are tightly linked: neutrons heat the coolant, fields stress the structure, temperatures shift material properties. A plant twin couples these models so information flows across their shared boundaries consistently. Getting the coupling right is as important as any individual model.
How models exchange
- Neutronics passes heating and damage rates to thermal and structural models
- The plasma state sets the neutron source and the heat exhaust to surfaces
- Thermal fields feed temperatures into structural and magnet models
- Structural deformation and magnet fields feed back to the plasma boundary
Weak versus strong coupling
Weak coupling exchanges information once per step and is simple but can lose accuracy or stability when the physics interact strongly. Strong coupling iterates the exchange within each step until the models agree, which is more accurate but more expensive. A twin chooses the coupling strength per interaction: strong where feedback is tight and fast, weak where it is loose and slow.
Timescale separation
The coupled physics span timescales from the fast plasma to the slow accumulation of structural fatigue. A twin exploits this separation, running fast-coupled subsystems together in the real-time path while updating slow interactions, such as damage accumulation, far less often. Mixing timescales naively wastes computation or misses fast feedback.
In the Kronos twins
For the Hyperion breeder, tight coupling among plasma, magnets, and control runs fast, while neutronics-driven breeding and structural damage update on slower cadences. For the burner, plasma and high-field plug coupling dominates the fast path while its low neutron fraction of 5.44 percent lightens the neutronics coupling. The coupled federation is verified against standalone codes and cross-checks today, with real cross-validation after the machines operate. See neutronics twin and thermal-hydraulic twin.