Effect of burning conditions on erosion shape of cathode in pulsed cathodic arcs

Vacuum cathodic arc plasmas have attracted much attention as a surface modification tool. For instance, metallic plasma ion implantation - deposition has demonstrated good effectiveness and versatility in the fabrication of sticking ceramic films in a plasma immersion configuration. Due to the pulsed working mode, the vacuum arc extinguishes frequently and periodically. This results in some consistent burning characteristics on the cathode rod after a burning period but some other features can also appear due to unstable burning of the vacuum arc and low efficiency of the cathode materials. The end configuration of the cathode rod is influenced by the pulse duration, arc current, gas pressure, etc. In a short pulse (e.g., pure metallic implantation), the cathode spot has insufficient time to spread to the entire surface before the arc extinguishes. Consequently the outer section of the cathode surface is preferentially eroded. A longer pulse duration can effectively avoid this local burning, for example, changing the arc duration from 0.4 ms to 2.0 ms. A 2.0 ms pulse arc results in a cathode surface without the protruding feature in the center and sometime even with a concave feature. Using typical operating conditions with a short pulse arc, a hollow cathode is experimentally proved to be very effective in avoiding the protruded features in the center as well as to stabilize the arc burning process. In this paper the influence of burning conditions on the eroded shape of the cathode end in the pulsed cathodic arc mode is presented.