Spatial charge effects in retarding field analyzer ion measurements in a cathodic vacuum arc

The ion energy distribution generated in a pulsed vacuum arc operated with a Ti cathode and N-2 filling gas is reported. A retarding field analyzer system is employed, for which the usual derivation of the ion energy spectrum has been modified to take into account spatial charge effects in the grid-collector region of the analyzer. It allows one to interpret the decrease in the collector current at collector bias voltages unusually low (even negatives) observed in this experiment, as well as in others. It is found that spatial charge effects are more marked when the arc operates with gas filling because of the creation (by charge-exchange processes) of low energy gaseous ions which are easily stopped by the potential hump created by the positive charge in the grid-collector region of the analyzer. (C) 2001 American Institute of Physics.