Charge state and residence time of metal ions generated from a microsecond vacuum arc

Metal ions generated from a microsecond vacuum arc were measured using a time-of-flight (TOF) method. A point-plane vacuum gap was fired by an impulse voltage to generate metal ions. The risetime and time constant for the decay of the arc current were 0.1 and 4.5 mu s, respectively. TOF ion currents were measured for variable ion extraction times after the arc ignition. At a lead cathode, Pb/sup +/ and Pb/sup ++/ ions were detected for ion extraction times less than 45 mu s. The average charge-state fractions of the Pb/sup +/ and Pb/sup ++/ ions were 91 and 9%, respectively. At a copper cathode, Cu/sup +/, Cu/sup ++/, and Cu/sup +++/ ions were detected for ion-extraction times less than 12.5 mu s, and the average charge-state fractions were 42, 41, and 17%, respectively. The residence times of the generated lead and copper ions were also discussed.>