Plasma Control System Architecture
A plasma control system links diagnostics, real-time computation, and actuators into feedback loops that hold a discharge on its intended trajectory.
What the PCS is
A plasma control system (PCS) is the real-time software and hardware that keeps a magnetically confined plasma inside its operating envelope. It reads measurements from diagnostics, estimates the plasma state, compares that state against a reference trajectory, and commands actuators such as coils, heating systems, and fueling. The loop runs continuously for the length of a discharge, from breakdown through ramp-down.
Layered structure
Mature control systems are layered. A fast layer handles time-critical loops like vertical stabilization at kilohertz rates. A feedback layer regulates shape, current, and density on millisecond timescales. A supervisory layer sequences scenario phases and arbitrates between controllers. Above these, an off-normal layer watches for faults and can trigger avoidance or safe shutdown.
This separation matters because the loops span very different bandwidths. Vertical position may need a response faster than a millisecond, while current-profile shaping evolves over the resistive timescale of seconds. Bundling everything into one loop would force the slow physics to run at the pace of the fast physics, wasting computation and coupling unrelated failures.
Determinism
A PCS is a hard real-time system: each cycle must finish within a fixed deadline, every cycle, or the control action is late and the plasma can move out of reach. This drives the use of real-time operating systems, dedicated networks, and bounded algorithms. Jitter, not average speed, is the enemy.
In the Kronos program
For the Hyperion breeder, a spherical tokamak, the architecture must give vertical stabilization very high priority because elongated, low-aspect-ratio plasmas are strongly vertically unstable. The burner generators use a different actuator set built around mirror plug fields and direct energy conversion. Because these machines are in design and simulation ahead of construction beginning in the second quarter of 2027, the control architecture is validated against models before it ever commands hardware.
- Diagnostics feed a state estimator
- Controllers compare state to reference
- Actuators apply the correction
- Supervisor sequences the whole discharge