Unified Analysis of the Metal Vapour Arc

Abstract

Abstract for given values of the total current density j and the cathode spot surface temperature T a unified and consistent calculation of the cathode drop, Uc , the electron temperature in the ionization region T _- the electron emission current density je , the ion current density j+ , and the extension of the space charge region lsp are presented. We find that the counter diffusion of plasma electrons into the space charge region plays a decisive role. It causes an effective space charge region extension lsp of a few plasma electron Debey lengths which in general is much less than the ion mean-free-path commonly used. Without the effect of the counter diffusing electrons, the theoretical results deviate from the experimental data by orders of magnitude. For the example of a Cu metal vapour-or vacuum arc the cathode drop is found to be approximately Uc = 15 [V], the electron temperature about T- =25000 [°K] and the ratio j+/j= 0.5. Since the analysis allows for multiple ionization the presence of multiply charged ions in the spot area can be calculated. The results of this investigation justify within the E-areas the approximations used in the analysis for the copper arc in an earlier investigation 1. Outside these E-areas a recalculation with the new results derived here may cause markable changes.