Ion current produced by a vacuum arc carbon plasma source

A vacuum arc carbon plasma source is described, in which an arc was ignited between a cathode and an anode having In aperture, by bringing the two electrodes into contact, and parting them while current was flowing. The inter-electrode gap length was varied. A focusing magnetic field was applied in the inter-electrode gap, and a toroidal magnetic field was applied to guide plasma through a toroidal duct. The influence of the arc current (I/sub arc/), gap length (L), and focusing magnetic field (B/sub f/) on the cathode spot motion, plasma behavior, and output ion current was studied. It was shown that with I/sub arc/=150-250 A and relatively weak B/sub f/, the spots moved on the cathode periphery, causing noisy arcing and fluctuation of the output ion current, while at a lower I/sub arc/ (50-100 A) and strong B/sub f/ (/spl ges/28 mT), there were fewer spots on the cathode surface, they tended to move toward the cathode center, the arc noise decreased and the average output ion current increased. With increasing L from 2 to 18 mm, the total ion current at first rapidly increased, and then saturated at L/spl ges/10 mm. Best performance of the carbon plasma source was obtained with an arc current chosen so that with a given field configuration, the cathode spots locate in the center of the cathode surface, and with strong magnetic fields in both the electrode and toroidal filter regions.