Effect of multiple current spikes on the enhancement of ion charge states of vacuum arc plasmas

Ion charge state distributions of vacuum arc ion sources are correlated to the arc operating voltage. Recent research has shown that an enhancement of ion charges via an increase of the arc voltage can be achieved utilizing t he transient processes that accompany an arc current spike. The idea invest igated is to further enhance the ion charge states by multiple current puls es. It is shown that although the ion charge states are enhanced compared t o quasi-dc operation, the application of a sequence of pulses does not lead to the desired additional increase in charge states. This can be attribute d to the additional plasma production that is caused by higher arc currents : The additional power supplied to the plasma is distributed over a larger number of plasma particles. One can expect that in the limiting case of man y current spikes, the ion charges state distribution approaches the one kno wn for arc plasmas at higher discharge current. (C) 2000 American Institute of Physics. [S0021- 8979(00)05612-7].