Power Flow and Cathode Erosion in a Vacuum-Arc Centrifuge

Measurements of discharge voltage, current, and cathode erosion rates in a vacuum-arc centrifuge are described. Such a centrifuge consists of a high-current vacuum-arc source imbedded in a uniform axial magnetic field. Plasma produced by the vacuum-arc discharge is collimated and rotated by the magnetic field. This rotation leads to radial centrifugal separation across the plasma column. Voltage-current characteristics reveal that the plasma resistance is independent of the axial magnetic field. A minimum turn-on voltage is required by the discharge, independent of the conducted current. This turn-on voltage is probably associated with sheath voltages at the electrodes. An appropriate electrical analog for the discharge is that of a diode in series with a pure resistance. Impedance matching of the electrolytic pulse-forming network to such a load is examined. Typically, 90 percent of the stored electrical energy is found to be coupled to the plasma load, making this a very efficient source for the centrifuge. Cathode erosion rates for carbon and magnesium cathodes are presented. These measurements are compared with those of other investigators at lower currents.