Control Actuator Inventory
The hardware the control stack can command - coils, power supplies, heating, current drive, and fueling - and each one's character.
Magnetic actuators
- Central solenoid: drives and regulates plasma current inductively
- Poloidal-field coils: set shape, position, and boundary flux
- Fast vertical-control coils: high-bandwidth stabilization
- Correction and RWM coils: cancel error fields and stabilize slow modes
- Power supplies: the amplifiers whose voltage and current limits bound all of the above
Heating and current drive
Neutral-beam injection and radio-frequency systems (ion- and electron-cyclotron, lower-hybrid) heat the plasma and can drive non-inductive current. They are slower to modulate than coils and are shared among several control goals - heating power, current-profile shaping, and localized mode control - so their allocation is a control problem in itself.
Fueling and impurity actuators
- Gas valves: fast edge fueling, easy to modulate
- Pellet injectors: deeper, more efficient core fueling
- Impurity seeding: controlled radiation for divertor and power-exhaust control
- Pumping: sets the particle-balance baseline
Actuator character matters
Every actuator has a bandwidth, a delay, a range, and a cost of use. Coils are fast and precise but limited in authority; beams are powerful but slow and coarse; gas is fast but inefficient; pellets are efficient but discrete. Good control matches each objective to the actuator whose character fits, rather than forcing one actuator to do everything.
The command surface
The actuator-management layer presents this heterogeneous hardware to the controllers as a bounded command surface with known limits and dynamics. Understanding the inventory - what each actuator can and cannot do - is a prerequisite for designing any loop that uses it.