Cathode ions from microsecond aluminum vacuum arcs

A triggered vacuum gap with a 1.25-mm-diam aluminum cathode, a nickel mesh anode, and a separate two-terminal gold trigger, were used to generate vacuum arcs of 60--90 A, 6--40 μs in duration. A retarding potential analyzer was used to investigate the cathode ion flux. A typical ion signal showed an initial peak about 10--20 μs after arc initiation, followed by a rapid decay, then the signal leveled off at about 30--35 μs to a fairly constant signal (plateau), which persisted until a few microseconds after the arc current was cut off; finally the ion signal decayed to zero. The initial peak was primarily composed of ions produced during the initial stage of the vacuum arc. The plateau represented ions produced after the arc settled down to a reasonably steady state. Conclusions were as follows: (1) The cathode ions produced during the initiation stage of such vacuum arcs are more energetic than those produced after the arc has settled down to a steady state, and (2) after this steady state has been reached, the cathode ion flux still appears somewhat more energetic than the cathode ion flux from dc vacuum arcs, although this may be because of the higher arc voltage caused by the relatively small ratio of electrode diameter to gap length in these experiments