Average Charge State Variation in the Cathode Material Ion Flow from the Low Current Microsecond Vacuum Arc

Abstract

Molybdenum and Copper-Chromium samples were used as the vacuum arc cathodes in the 4-microsecond vacuum arc discharge. The pulse source was an LC-line with a quasi-rectangular pulse shape. Arc current varied from units of ampere to 125 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 for both materials. The decrease of the average charge was due to a decrease of the high-ionized ion fractions and an increase of low-ionized ion fractions (+1 and +2 for molybdenum, and +1 for copper and chromium). 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 and refractory cathodes, such as molybdenum.