A SELF-CONSISTENT MODEL FOR THE CATHODE FALL REGION OF AN ELECTRIC-ARC

A one-dimensional model of the non-equilibrium plasma region adjacent to an electric are cathode is developed. The collisionless space-charg e zone (sheath) and the hydrodynamically described ionization zone (pr e-sheath) are connected to a unified model. In the pre-sheath, ionizat ion, diffusion and decoupling of electron and heavy-particle temperatu re are considered. The voltage drop in the space-charge zone is comput ed self-consistently including thermionic electron emission at the cat hode surface. This unified model yields the overall cathode potential drop (cathode fall), the extent of the non-equilibrium region and the net energy flux towards the cathode surface. In this paper, the model is applied to an argon are plasma at atmospheric pressure with a thori ated tungsten cathode, as is typically used for welding of stainless s teel materials.