Solid target boronization of the MST reversed-field pinch during pulsed discharge cleaning

A solid rod of hot-pressed boron carbide is currently being used as the source of boron during boronization of MST. In previous work the authors have demonstrated that boronization can be effectively accomplished by insertion of a low apparent density B4C rod into the edge hydrogen plasma of normal high-power RFP discharges. The authors have now extended that technique and can boronize MST by inserting a negatively biased B4C rod into pulsed discharge cleaning (PDC) helium plasmas. The same positive results of reduced impurity contamination and particle reflux are achieved with this new boronization method. The bias for the target is provided by the ohmic heating transformer which is pulsed to produce the PDC discharges. Current flow through the B4C rod is limited by an inductor. The amount of hydrogen in the amorphous boron carbide films is minimal because the only hydrogen in the PDC plasma is that left over from RFP discharges