High ion charge states in a high-current, short-pulse, vacuum arc ion source

Ions of the cathode material are formed at vacuum are cathode spots and extracted by a grid system. The ion charge states (typically 1-4) depend on the cathode material and only a little on the discharge current as long as the current is low. Here we report on experiments with short pulses (several mu s) and high currents (several kA); this regime of operation is thus approaching a more vacuum sparklike regime. Mean ion charge states of up to 6.2 for tungsten and 3.7 for titanium have been measured, with the corresponding maximum charge states of up to 8+ and 6+, respectively. The results are discussed in terms of Saha calculations and freezing of the charge state distribution. (C) 1996 American Institute of Physics.