The Linear Feedback Stabilization System for Scyllac

A linear feedback stabilization system is being designed, tested, and constructed for the 5-m toroidal sector of Scyllac. Each closed loop consists of an optical plasma position detector, resolver and preamplifier, power amplifier, and one-turn load coil to apply the magnetic field for plasma position control. This paper describes the entire system; however, the major engineering effort is on the power amplifier and therefore is the point of major emphasis in this paper. The final stage of each closed loop in the linear power amplifier is made up of two Machlett ML-8618 magnetically-beamed power tubes operated in push-pull at plate currents up to 500 amperes. The output is coupled through a step-down transformer to the load so that up to 5 kA will be available for plasma position control. The design goal is to have a risetime of 0.2 ¿sec in the load coils. There are thirty closed loops which together can provide a peak power of 1 Gigawatt.