Optimizing Plasma Scenarios
A scenario is the full time trajectory of a discharge; optimizing it means shaping the whole path, not just a steady operating point.
What a scenario is
Running a plasma is not just holding one state; it is a trajectory from breakdown through ramp-up, a flat-top phase, and a controlled ramp-down. A scenario specifies how current, density, heating, and shape evolve over that whole path. Optimizing the scenario means choosing the trajectory that reaches the target safely and efficiently.
Why the path matters
- Ramp-up can trigger instabilities if done too fast or in the wrong order.
- The flat-top must sit inside the safe operating envelope.
- Ramp-down must avoid disruptions as current unwinds.
- The whole path must respect actuator limits.
Optimization over trajectories
Scenario optimization is a trajectory-optimization problem: find the time-dependent actuator commands that reach the target while satisfying constraints along the entire path. It uses reduced-order models to evaluate candidate trajectories and optimization to search among them.
Testing against the twin
Candidate scenarios are tested against the digital twin before being run on hardware, so a scenario is vetted end to end in simulation first. This is how the Hyperion breeder's operating scenarios are being developed ahead of first plasma.
Both machines
The tandem-mirror burner has its own scenario problem centered on establishing and holding the plug potentials, optimized with the same trajectory approach even though the physics differs.
Robustness
A good scenario is robust to uncertainty, working across the credible range of plasma conditions rather than only on the nominal case.