Pellet Injection Timing

Cryogenic pellets deliver deep, discrete fuel; L1 times each injection precisely for density profile control, pacing, and disruption mitigation.

Discrete deep fueling

Pellet injection fires small cryogenic fuel pellets deep into the plasma, depositing particles where gas puffing cannot reach. Unlike continuous gas flow, each pellet is a discrete event, so control is about timing and sizing: when to fire, how large, and how fast. L1 schedules injections against the density-profile objective.

Timing as the control variable

Because a pellet's effect is a step in density, the outer loop controls the injection rate and phase rather than a continuous flow. L1 fires pellets on a deterministic schedule derived from the density error and profile target, with each shot's launch precisely timed relative to the plasma state and, where relevant, to the ELM/edge cycle for pacing.

Uses

• Deep density-profile control beyond the reach of edge gas fueling.
• Fuel throughput consistent with the breeder's tritium/deuterium mix.
• Edge pacing to manage the edge in the ELM-free strategy.
• A pathway for disruption mitigation deposition.

On the breeder, pellet fueling supports reaching and holding the density needed for the operating point behind Q_sci 3.076 and 85.0 MW, and it interacts with the fuel cycle's isotope balance since pellets carry a defined D-T composition. The injector's deterministic timing lets L1 place each pellet's density perturbation predictably.

Determinism of a discrete actuator

A discrete actuator is deterministic when its trigger-to-launch latency and its launch-to-deposition transit are bounded and repeatable. L1 characterizes both so the density step lands where the controller expects. Pellet and gas actuation are arbitrated together, and both draw fuel from the balance managed by the fuel cycle.