Layer 6: Scenario and Trajectory Supervision
The layer that schedules references through a discharge - ramp-up, flat-top, ramp-down - and adapts the plan as conditions evolve.
A discharge is a plan
Every shot follows a scenario: a planned trajectory of current, shape, density, and heating from breakdown through ramp-up, flat-top, and controlled ramp-down. The scenario layer holds that plan and issues the time-varying references the lower loops track. It is the layer that knows what the discharge is supposed to be doing at each moment.
Feedforward plus feedback
Scenarios are largely feedforward - a precomputed waveform of targets - but the layer also adjusts references based on the estimated state. If the plasma is denser than planned, it may delay a heating step; if a limit is approaching, it may flatten a ramp. This is supervisory control: it does not command actuators directly, it reshapes the goals the fast loops pursue.
Segments and events
- Ramp-up: establish current and shape while avoiding early instabilities
- Flat-top: hold steady conditions and the intended plasma regime
- Transitions: heating steps, fueling changes, confinement-mode changes
- Ramp-down: reduce current and stored energy on a safe path
- Event handling: branch to alternate plans on off-normal conditions
Feasibility checking
Before it issues a reference, the scenario layer checks that the actuator-management layer can plausibly deliver it. Commanding an infeasible target - more shaping than the coils can provide, or a density above a stable limit - would push lower loops into saturation. The supervisor's job includes refusing to ask for the impossible.
Coordination with prediction
The scenario layer listens to the predictive digital twin. If the twin forecasts that the current plan leads toward a limit or a disruption, the supervisor selects a pre-validated alternative branch - a softer ramp, an earlier ramp-down - rather than continuing blindly. Plans are living, not scripts.