Estimate of the Cathodic Arc Spot Size in a Nontransferred Arc Plasma Torch by Comparing the Results of a Numerical Analysis with the Experimental Results

Abstract

The cathodic arc spot size of a nontransferred arc plasma torch is an important parameter that can predict the thermionic emission phenomenon for arc channel formation and the ion flux that impinges on the cathode surface. However, experimentally measuring the cathodic arc spot size is difficult. Therefore, in this study, a numerical analysis to estimate the cathodic arc spot size was performed according to the input current level with a tungsten cathode by using a self-developed magnetohydrodynamics (MHD) code. The various current environments were compared as low (0.424 A), intermediate (35, 60, and 90 A), and high (350 A) current levels. At each input current level, the arc voltage was calculated for the arc spot sizes from 1.0 to 4.0 mm. The appropriate cathodic arc spot size was estimated by comparing the measured and the calculated voltages. As a result, the cathodic arc spot radius had a valid difference depending on the input current level, and the influence of the cathodic arc spot radius was particularly sensitive under the low (0.424 A) current condition.