Gas-Puff Servo-Valve Interface
Piezo servo valves give the fast, shallow end of the fueling authority spectrum; their interface is a millisecond flow-command loop with hard interlocks.
Role in the fueling mix
Gas puffing is the fast, edge-localized complement to deep pellet fueling on the breeder, and it is also used for edge density and radiative control. On the burner it feeds the plug and central cell. The interface commands piezoelectric servo valves that respond in milliseconds — far faster than a pellet but with shallow deposition.
Command and interlock
# gas-puff flow command (L1)
flow_cmd = density_mpc(n_e_edge, n_ref).fast
if plenum_P_ok and vac_valve_open and not disruption_lock:
piezo_valve.set(flow_cmd) # ms response
else:
piezo_valve.close() # fail-closedThe valve is fail-closed: any loss of plenum pressure, vacuum-boundary fault, or disruption lock drives it shut. This is enforced at the L1 edge so a supervisory fault cannot leave gas flowing into the vessel.
Interlock table
| Plenum P ok | Vac boundary ok | Valve enable |
|---|---|---|
| 0 | 0 | 0 |
| 0 | 1 | 0 |
| 1 | 0 | 0 |
| 1 | 1 | 1 |
- Owner: L1 for the flow loop; L3 for the edge-density setpoint.
- Timing: milliseconds, well inside the shape/density MPC cycle.
- Cross-link: shares the vacuum feedthrough and vacuum interlocks.
Calibration maps valve drive to mass flow at a known plenum pressure and is re-checked as the piezo ages. Design-and-simulation specification, exercised against the twin.