Angular Distribution of Ions in a Vacuum Arc Plasma With Single-Element and Composite Cathodes

The angular distribution of the different cathode materials and gaseous ion flow from vacuum arc plasma is investigated. A metal-vapor-vacuum-arc-type ion source and a time-of-flight mass spectrometer were used. The experiments were performed using a range of different cathode materials, including C, Al, Zn, Cu, Ti, Co, Cr, W, Pb, Cu0.7Cr0.3, W0.4Co0.17C0.43, and Zn0.4Pb0.6, over a range of vacuum arc discharge parameters. It was shown that, for all materials, the fraction of singly charged ions on the axis of the system is much less than that of multiply charged ions, but at the edges, the fraction of single-charged ions is greater than that of multiply charged ions; for composite cathodes consisting of light and heavy materials, there were substantially less light atoms on the axis than heavy atoms, while the opposite situation prevailed at the edges, but for cathodes with similar mass, the angular distributions of the materials were very close to each other. The velocities of ions of different materials in the composite cathode were different, but light ions had a higher velocity than those in a pure cathode plasma. With admission of gas, the angular distribution of Ar+ became more isotropic with increasing pressure, while the metal ion distributions changed only minimally.