Arc modulator for the TFTR neutral-beam ion source

A discussion is presented of the protection of the tokamak fusion reactor neutral-beam ion source, located at the Princeton Plasma Physics Laboratory. The system design is based on three operational protection requirements that include provisions for ion-source current pulse matching, ion-source fault current extinction, and metallic fault current extinction. A power circuit configuration satisfying these requirements is illustrated and briefly described. Simplified analytical expressions relating the protection requirements to the circuit parameters are developed. Experimental findings are in good agreement with a computer simulation of the circuit model, although several side effects introduced by the circuit configuration have been observed. The side effects observed include ion-source current overshoot and the existence of a negative ion source current. Modifications to counteract these side effects are briefly described