Extractable, elevated ion charge states in the transition regime from vacuum sparks to high current vacuum arcs

Metal ions were extracted from pulsed discharge plasma operating in the transition region between vacuum spark and vacuum arc. At a peak current of about 4kA, and with a pulse duration of 8μs, we observed mean ion charges states of about 6 for several cathode materials. In the case of platinum, the highest average charge state was 6.74 with charge states present as high as 10, and with gold we found traces of charge state 11. At higher currents, nonmetallic contaminants started to dominate the ion beam, preventing further enhancement of the metal charge states.