Time and Energy-resolved Average Ion Charge States in Pulsed Cathodic Vacuum Arc Plasmas of Nb-A1 Cathodes as a Function of Ar Pressure

Abstract

Despite substantial progress in the last decades, the physics responsible for the plasma properties of cathodic vacuum arcs are still a matter of dispute, particularly for multi-element cathodes. The plasma analysis is complicated by the generally occurring neutral background of metal atoms, which perturbs initial ion properties. By using a time-resolved method in combination with pulsed arcs and a Nb-Al cathode model system, we investigate the influence of cathode composition on ion properties, while making the influence of neutrals visible for the observed time frame. This model system consists out of two different Nb-Al compositions with the the atomic ratios 75/25 and 25/75, as well as pure Nb and Al cathodes. The results visualize average charge states of Nb and Al ions of $600 \mu\mathrm{s}$ plasma pulses, extracted 0.27 m from the cathode, resolved in energy and time. In addition to high vacuum at a base pressure of 10–4 Pa, results at three elevated Ar gas pressures (0.04 Pa, 0.20 Pa and 0.40 Pa) are shown. For high vacuum, ion properties were generally found to be strongly dependent on the cathode material, but deviating from a simple linear interpolation between the ion properties from Nb and Al cathodes. The influence of an inert background gas is analyzed by comparing these results with those at increased pressure, which show reduced ion charge states, up to a situation where mostly Nb2+ and Al+ ions are detected.