Analysis of Electrode Phenomena in the High-Current Arc

Abstract

An analysis is made of the phenomena at the electrodes of a high-current short-time arc. It is shown that the input power density to the anode spot is in the range 5×104 to 1×106 watts/cm2. To a first-order approximation, all this power can be carried off by evaporation. Power conducted into the metal and lost by radiation is negligible in the probable operating range. For most materials, the anode spot is probably considerably above the boiling temperature. The process of evaporation holds the spot temperature constant at a value such that the input power and evaporation power are equal. Experimental data indicate that for any given metal the anode spot temperature is that for which the evaporation power density is at least 3×105 watts/cm2. As an example, for copper the theoretical limits of temperature are 2490 to 3040°K, while experimental data indicate a temperature of 2920°K. Other metals considered are: Ag, Al, C, Fe, Mo, Sn, Ti, W, Zn, Zr. It is also shown that for the maximum power input that can be expected at the cathode, the thermionic emission current density is very small compared to the observed values of current density.