Speaker
Description
Cathode erosion of vacuum arcs is due to emission of high-speed plasma jet of energetic ions and a liquid droplet ejection from a melted cathode surface. Most of the research (experimental and theoretical) has been devoted to studies of the ionic erosion. However, droplet emission could be as important (and even prevalent) mechanism responsible for the cathode erosion. According to a widely accepted model [1], the ejection of the droplets is caused by a very high pressure of vaporized cathode material at the foot of the cathode spot. That pressure expels the melt from the bottom of the cathode liquid pool thus creating a crater on the cathode surface. In many existing works, the expulsion rate has been calculated. However, at present, these is no model that would allow one to calculate what fraction of the expelled metal remains at the cathode in the form of a rim and what fraction leaves it in the form of droplets. In our presentation, we will suggest a simple model, which allows one to find that fraction. The central point of our model is the solidification of the molten metal extruded from the crater. No adjustable parameters are used in the model, which operates only with experimental data. In the first part of our presentation, we will describe the model and calculate the droplet erosion rate in a vacuum arc. The satisfactory agreement with experimental data for the erosion rate has been obtained. In the second part, the calculations of the erosion rates for high-pressure arcs will be presented. Comparison of simulation results with experimental data shows satisfactory agreement and may explain the observed non-monotonic dependence of the erosion rate on gas pressure.
Acknowledgment
This work is supported by the DOE SBIR Project DE-SC0015746.
References
[1] G W McClure. Journal of Applied Physics 45, 2078 (1974)