Coupling Physics Domains
Real systems obey many kinds of physics at once; coupling separate solvers correctly is where much of the difficulty and the error lives.
When One Physics Is Not Enough
A real device rarely obeys a single physics. A fusion plasma is at once a fluid, an electromagnetic system, and a source of heat and particles interacting with materials. Multiphysics coupling joins solvers for these different domains so their mutual influence is captured, because each domain changes the conditions the others operate in.
Coupling Schemes
- Monolithic: solve all the coupled physics together as one large system; accurate but demanding.
- Partitioned: run separate solvers and exchange information between them; modular but requiring care.
- Explicit exchange: pass data once per step; simple but can be unstable or inaccurate.
- Iterative exchange: pass data back and forth within a step until consistent; more robust, more costly.
Where Errors Hide
The interface between domains is where coupling errors concentrate: mismatched grids, inconsistent units, differing time steps, and data passed at the wrong moment. Two individually verified solvers can produce a wrong coupled result if the exchange between them is flawed. The coupling itself must be verified, not just the components, and its seam deserves dedicated testing.
Stability of the Coupling
Even when each solver is stable alone, a weak coupling scheme can make the combined system unstable or drive it to a wrong steady state. Explicit, one-way exchange is cheap but can miss strong feedback between domains; iterating the exchange to consistency within each step is often needed when the domains are tightly coupled. Matching the scheme to the strength of the coupling is a key design choice.
At Kronos
The breeder and burner designs involve coupled plasma, electromagnetic, thermal, and material physics. Kronos work treats the coupling interfaces as first-class objects, agreeing on units, grids, and exchange points, and verifies the coupled behavior rather than assuming that correct components guarantee a correct whole.