It is an alternative regulator where the output voltage is controlled by a knob that may be changed.
T1 is a 15 Volt audio frequency transistor rated at 6000 amps. This is the shunt regulator. The Diode Ring DR1 rated at 6000 amp and 15 volts takes current from the TNR (Thermonuclear Reactor) Power coil W1 to the transistor.
DR2 is the detector of the voltage the TNR has reached; I have omitted the smoothing capacitor that is connected across the output of the diode ring rectifier. This rated at 15 volts 0.5 amp
W3 supplies the current to a commercial off the shelf power supply unit comprising a diode ring rectifier smoothing capacitor and regulator rated at 100 amps 24 volt.
The power amplifier takes the output from the op amp and increases the current it may deliver to probably 100 amps to drive the 6000 amp transistor T1.
The potentiometer 10K linear and is the reference for the op amp. This will be fed from a zener with an emitter follower to feed the op amp or another op amp.