Coil Power-Supply Control
Power supplies convert grid power into the precisely regulated currents the magnet coils need, and their fast inner loops underpin all magnetic control.
What the supplies do
Each controllable coil is driven by a power supply, usually a thyristor or transistor converter, that turns AC grid power into a regulated DC current. The supply is the actuator through which every magnetic-control command reaches the plasma: shape, position, and stability loops all ultimately ask a supply to change a coil current.
Current regulation
The innermost loop regulates coil current to a reference by controlling the converter output voltage, because coil current responds to applied voltage through the coil inductance. A measured current from a DC transducer closes the loop. This loop is fast and tight, so the higher-level plasma controllers can treat coil current as a directly commandable quantity.
Voltage headroom and limits
How fast a coil current can change is limited by the supply's available voltage, since dI/dt equals applied voltage divided by inductance. Vertical-stability coils need high-bandwidth supplies with ample voltage; slowly varying coils need less. Supplies enforce current, voltage, and rate limits, and they must handle the reactive power and disturbances that pulsed operation imposes on the grid connection.
- Convert grid AC to regulated coil DC current
- Inner current loop tracks the commanded reference
- Voltage headroom sets maximum current slew rate
- Enforce current, voltage, and rate limits
Protection
Supplies protect their coils and themselves against over-current, over-voltage, and short circuits, and they coordinate with quench protection so that a fault trips the breaker and inserts the dump path cleanly. For superconducting coils the supply also manages the current leads' thermal load. In the Kronos designs the coil-supply architecture is specified for the breeder's and burner's high-field coils as part of the simulation and design basis, not as installed equipment.
Reliable current regulation is the foundation the whole magnetic-control stack is built on.