Multiphysics Coupling
Fusion phenomena are coupled: plasma, neutrons, heat, and structure influence each other, so their models must be solved together.
Why coupling matters
In a fusion machine the plasma sets the neutron source, the neutrons heat and damage the structure, the heat drives thermal stress, and the resulting deformation and temperature feed back on the fields and the plasma. Solving each in isolation gives an answer that ignores these feedbacks and can be badly wrong.
How models are coupled
- One-way coupling passes results from one model to the next without feedback.
- Loose coupling exchanges data between models between steps.
- Tight coupling solves the models together as one system.
- The choice depends on how strong the feedback is and how much accuracy is needed.
The computational cost
Coupled solves are expensive because each physics is already heavy and the coupling adds iterations. This is a major reason multiphysics runs on HPC and why reduced-order models and surrogates are used where full coupling is unaffordable.
In the Kronos design
Closing the Hyperion design point is fundamentally a coupled problem: the field, current, heat exhaust, breeding, and structure must all be consistent at once. Treating them separately would produce a point that looks closed but is not.
Both machines
The tandem-mirror burner has its own coupling between plug fields, plasma potential, and direct energy conversion. The framework for coupling models transfers even as the specific physics changes.
Verification
Coupled results are checked for consistency, such as conserved energy across the coupling interface, part of verification and validation.