Erosion rate in a vacuum arc and in a gas arc at threshold currents

The present paper reports an experimental study of the erosion rate of pulsed arcs in vacuum under the influence of surface conditions (contaminants and clean), and ambient gases (argon, nitrogen with high purity introduced with pressures 600 Torr) with cold cathodes. Erosion rates have been studied of wires cathodes from Au, Ag, Cu, W prepared by heating less then melting temperature prior to arcing. Such surfaces may be sufficiently clean also without preceding erosion. In both systems the ion current streaming was measured by a biased collector. It appears that the erosion rates are not changed by outer influences background gas. The discrepancy between the ion collection and weighing methods clearly points to the contribution of macroparticles to cathode erosion. It has been shown that macroparticle mass losses are indeed important. Experimental results show that the mass of cathode material removed by the macroparticles flux is greater than the mass of cathode material leaving in form of ions. Besides ion current measurements also used the weighing method to determine the total erosion rate of cathode materials. From the analysis of the erosion rate as a function of charge transferred by the vacuum arc and arc in gases were concluded that the total erosion rate approaches the ion erosion rate if the charge transferred by the arc is small. The dependence of the ion current from vacuum arc current is in linear relation. The approximate independence of arc current is consistent with findings that increasing the arc current leads to an increase in the number of emission centers rather than changing the character of these centers.