Neutral-Beam Injection Actuator

Neutral-beam heating is a primary actuator on both machines; L1 modulates delivered beam power deterministically for heating, current drive, and fast protection.

Beams as an actuator

Neutral-beam injection (NBI) delivers energetic neutral atoms that ionize and heat the plasma, and can drive current and momentum. For control, NBI is an actuator whose delivered power and, where steerable, deposition location are commanded by L1. The breeder uses beam power for heating and current-profile influence; the burner uses beams to sustain the plug and mirror-cell populations.

Deterministic modulation

The beam driver closes a fast inner loop on delivered power, tracking L1's setpoint. Power can be modulated on the control timescale for feedback on stored energy or plug density. Because delivered power is a physical quantity with device limits, the driver clamps commands to the beam's safe operating envelope locally.

Fast protection: beam notching

NBI participates in protection through notching: on a disruption precursor or a plug fault, L1 can cut or notch beam power within the deterministic window to remove drive from an evolving instability. This is a fast, reversible actuation that buys time for slower mitigation, and it is arbitrated below protection priority.

• Command variable: delivered beam power (and steering, where available).
• Inner loop: driver regulates power with bounded response.
• Protection: fast notch/cut on precursor within the 10 µs class.
• Envelope: local clamps to beam-source and duct limits.

Two roles, two machines

On the breeder (Hyperion), beams contribute to reaching and holding the operating point that yields Q_sci 3.076 and 85.0 MW of fusion power, and to current-profile control alongside the 9.66 MA plasma current. On the burner, beams sustain the end-plug and central-cell populations that hold the ambipolar potential. In both, L1 treats the beam as a fast, envelope-limited power actuator.