Temperature measurement and metallurgical study of cathodes in dc arcs

The occurrence of arc-cathode erosion in pure tungsten and two-percent-thoriated tungsten cathodes was investigated. Specifically, measurements of cathode temperature distribution as well as observations of cathode spot behavior and cathode metallurgy after arcing were obtained using different plasma gases and cathode geometries. The results demonstrated that cathodes should be designed to avoid overcooling which leads to steep temperature gradients and ion bombardment.