Beam Notching for Fast Protection

Cutting or notching neutral-beam power within microseconds removes drive from an evolving instability, a fast reversible protection actuation on both machines.

What notching does

Beam notching is the rapid, brief removal of neutral-beam power. When L1 detects a fast precursor — a disruption cue on the breeder or a plug/potential fault on the burner — cutting beam drive can arrest an instability that the beam was feeding, or protect beam hardware from an adverse plasma state. It is fast, reversible, and low-regret, which makes it a first-response protection lever.

Timing

Notching must land inside the fast-protection window. The command path — precursor detection, arbitration at protection priority, delivery to the beam driver, and power cut — is engineered within the deterministic bound so the notch takes effect before the instability has grown. The beam driver supports a fast power step precisely so this actuation is available on demand.

Why reversible protection matters

• A notch removes drive without terminating the discharge.
• If the precursor clears, power ramps back and operation continues.
• If it does not, slower mitigation proceeds with time bought.
• Low false-trip cost encourages sensitive, early triggering.

Because a notch is cheap to recover from, L1 can afford to trigger it on relatively early, uncertain precursors — the opposite trade-off from a magnet dump, which is protective but disruptive. This graded response, from notch to full mitigation, lets the control plane match action severity to threat confidence.

Coordination

Notching is one member of a coordinated protection repertoire that also includes gas/impurity actuation and, at the extreme, discharge termination. L1 sequences these by severity, with the magnet failsafe underneath as the independent floor. On the burner, the analogous fast lever pairs beam notching with DEC fault ride-through to protect the conversion train.