Scenario and Trajectory Control
Designing and executing the time-varying reference trajectories that carry a plasma safely from breakdown to controlled termination.
What a scenario is
A scenario is the full plan of a discharge: coordinated waveforms of plasma current, shape, density, heating, and current drive versus time. It is designed offline to reach a target plasma regime while staying inside every stability and hardware limit at each instant, and executed as the reference the control loops track.
The phases
- Breakdown and burn-through: initiate the plasma and establish current
- Ramp-up: raise current and build the shape while avoiding early modes
- Flat-top: hold the target regime for the useful part of the discharge
- Ramp-down: reduce current and stored energy on a safe path
- Termination: land the plasma softly or trigger protection if needed
Trajectory feasibility
A trajectory is only valid if, at every point along it, the actuators can deliver the demand and the plasma stays inside its limits. Scenario design is therefore constrained trajectory optimization: find waveforms that reach the goal while respecting actuator bounds, volt-second budget, and stability margins throughout - not just at the endpoint.
Feedforward and adaptation
The scenario is executed mostly as feedforward, with feedback trimming residuals. But real plasmas deviate from plan, so the scenario layer adapts references in response to the estimated state and the predictive twin: flattening a ramp that is heating too fast, delaying a step until density settles, or branching to an alternate plan on off-normal conditions.
Design context
For the Kronos breeder Hyperion, reference scenarios target a 9.86 MA plasma with strong shaping and negative triangularity, computed in simulation. These trajectories are design studies used to test the control approach, not records of operating hardware. Construction is planned to begin in Q2 2027.