Gas-Puffing Servo Valves

Fast piezo servo valves meter fuel and impurity gas into both machines; L1 modulates flow deterministically for density control and edge management.

Gas puffing as fueling and control

Gas puffing injects neutral fuel (or impurity) gas through fast servo valves. It is the primary fine-fueling actuator: L1 modulates valve opening to control plasma density, feed the edge, and — with impurity species — radiate power where wanted. The valves are piezo-driven for fast, proportional response on the control timescale.

Deterministic flow control

Each valve driver closes a fast loop on commanded flow (or valve position as a flow proxy), so L1's density controller sees a predictable actuator. Because gas transport into the plasma has its own delay, the valve response must be fast and repeatable for the outer density loop to remain stable; jitter in valve actuation would translate into density ripple.

Roles per machine

• Breeder: line-averaged density control, edge fueling for the ELM-free regime, impurity seeding for radiative divertor operation.
• Burner: central-cell and plug fueling to support the density profile that holds the ambipolar potential.
• Both: gated by vacuum permissives — valves enable only in a proven vacuum state.

On the breeder, fine density control interacts with the edge regime: pushing density too hard can move the edge toward an ELMy state, so the fueling loop respects edge limits. On the burner, fueling supports the plug density that is central to confinement.

Coordination with pellets

Gas puffing handles fine, fast density trimming; pellet injection handles deeper, larger fueling and mitigation. L1 coordinates the two so they do not fight, using gas for continuous regulation and pellets for discrete deposition. Both flow through the deterministic driver layer and are gated by the vacuum interlocks.