A MATHEMATICAL-MODEL FOR THE STOCHASTIC-BEHAVIOR OF SPECIES NEAR THE CATHODE IN ARC-WELDING

The velocity distributions of ions and electrons are evaluated in the region intermediate between the plasma bulk and the so-called drift re gion. A largely analytical one dimensional model is provided in which the motion of particles is described by the Langevin equation taking i nto account the effect of the electric field. In the case of ions, thi s produces a non-stationary Maxwellian distribution of velocities. For the much lighter electrons, the effect of the electric field is here described using the Druyvesteyn velocity distribution. The non-station ary Maxwellian character of the ion distribution may explain the signi ficant differences in temperature inferred from measurements, causing different spectral lines which may arise at different distances from t he cathode.