Surrogate Model Generation
Building fast emulators of expensive solvers so the twin can evaluate neutronics, transport, and equilibrium in real time.
Emulating the expensive solvers
Many L0 solvers, gyrokinetic turbulence, Monte Carlo neutronics, coupled transport, are far too slow for the real-time twin. Surrogate model generation is the L0 process that replaces each with a fast emulator: a model trained to reproduce the solver's input-output mapping in a single cheap evaluation. Surrogates are what let the twin carry physics it could never solve live.
Design of experiments
A surrogate is only as good as the samples it learns from. Kronos uses design-of-experiments sampling, space-filling designs over the input parameters, to run the expensive solver at well-chosen points, then fits the surrogate to that data. The sampling strategy matters more than raw sample count, because coverage of the input space determines where the surrogate can be trusted.
- Space-filling sampling of solver inputs
- Fitting emulators to solver outputs
- Error estimation across the input domain
- Active-learning to add samples where error is high
Knowing the surrogate's limits
Every surrogate carries an error estimate and a domain of validity. Outside the sampled region, its output is extrapolation and must not drive control. Kronos records these bounds with the model so the twin knows when a prediction is inside its trained envelope and when it should defer or trigger a fresh solve. A surrogate that hides its uncertainty is dangerous.
Surrogates serve both machines and many modules. Breeder neutronics response tables, burner ambipolar-potential emulators, transport-coefficient surrogates from gyrokinetics, and equilibrium surrogates all follow the same generate-validate-bound pattern. The physics differs; the discipline of building a bounded, validated emulator does not.
Surrogate generation is coupled to retraining: as new solver runs accumulate, surrogates are refreshed and their validity domains extended. This is how the twin's fast physics stays anchored to the slow ground truth, and it is a central reason the offline foundation exists.