Investigation of Factors Influencing the Charge-state Composition of the Cathode Material Ions in the Plasma of Low-current Vacuum Arc

Abstract

Copper and Copper-Chromium samples were used as the vacuum arc cathodes in the 4 microsecond vacuum arc discharge. Pulse source was an LC-line with a quasi-rectangular pulse shape. Arc current varied from threshold current to 100 A. Charge state distribution and the average charge state of the cathode material ions were measured via the Thomson spectrometer with automated image recording and digital data processing. It was found that the ion charge state distributions were close to the classical data at the hundred-ampere currents, and the average charge state significantly decreased with the arc current decrease. The decrease of the average charge was due to a decrease of the high-ionized ion fractions and an increase of single-ionized ion fraction. In comparison with early experiments with copper cathodes, it was confirmed, that the effect was not the product of the spark stage plasma influence. And besides the hydrogen ions fraction in the plasma, the arc current value itself was a key factor of the charge distribution variation effect. This effect, observed earlier only for copper cathodes, confirmed to be a feature of the plasma generation in low-current vacuum arcs on the CuCr cathodes. Additionally, the measurement results showed, that average charge states of the cathode material component ions can differ from the average charge state in case of the pure Cu and Cr cathodes.