Dependence of the plasma composition in the low-current vacuum arc discharge on CuCr cathode on the current value and surface conditions

Abstract

The dependence of the ion flux mass-charge composition from the vacuum arc plasma with the CuCr cathode on a value of the discharge current was investigated via the Thomson spectrometer with automatic signal registration and analysis. The microsecond arc was formed in a millimeter gap between CuCr cathode and copper anode under high vacuum conditions. The arc current was changed within the range from a few to tens of ampere. At the highest currents the plasma composition corresponded the elemental composition of the cathode surface. The fraction of the chromium ions significantly decreased with the arc current decreasing below 30 A. There was noticeable increasing of the fraction of the chromium ions in the plasma at the discharge currents near the threshold values for the cathode materials. The effect appeared on coarse-grained non-melted cathode surfaces, and vanished after a multiple arcing.