ANALYSIS OF THERMAL NONEQUILIBRIUM IN THE NEAR-CATHODE REGION OF ATMOSPHERIC-PRESSURE ARCS

The electron energy equation for the near-cathode region of an are dis charge is analysed qualitatively. Estimates based on the most recent d ata of temperature and current density in atmospheric-pressure arcs sh ow that deviations of the electron temperature from the heavy-particle temperature are not likely to be localized in a near-cathode layer of thickness of the order of 100 mu m, as most authors have assumed, but extend over distances of the order of the radius of the cathode spot. It is shown that electron heat conduction dominates all other process es affecting the electron temperature in the ionization layer and the electron temperature is, to a first approximation, constant across the layer. In order to find it, the multi-dimensional electron energy equ ation in the expansion zone should be solved. A boundary condition for this equation at the edge of the ionization layer is established.