Mass-to-charge composition of high-current vacuum arc plasmas with Cu–Cr cathodes

Abstract

Copper–chromium composite electrodes are widely used in high-current vacuum interrupters. Current interruption may trigger a vacuum arc between such electrodes. The operational dynamics of interrupters is determined by the vacuum arc parameters. We have employed a time-of-flight spectrometer to study the mass-to-charge composition of plasma ions in the arc discharge with Cu–Cr electrodes at a current density of 1 kA cm−2 as is typical for the arc in interrupters. We find that the average charge states of copper and chromium ions depend on their fractional content in the cathode material. With the percentage of chromium ions increasing from 0% to 50%, the average charge state of chromium ions 〈Q〉Cr increases from 1.98 to 2.13, while that of copper ions 〈Q〉Cu decreases from 2.15 to 1.95. We observe a decrease in the average charge states of both copper and chromium ions over the duration of the arc pulse. The results of our investigations of arc plasma composition may be useful for analysis of mass and charge transport in interrupters.