Role of metallic neutrals and gaseous molecular ions in a copper cathodic arc operated with oxygen gas

The plasma-neutral gas structure generated in a copper cathodic arc operated with oxygen gas at a constant current level of 100 A has been investigated by employing a Langmuir spherical probe and a calorimetric technique. The plasma potential and electron temperature at several axial distances (between 10 and 25 cm) from the cathode surface and for different O-2 pressure values (between 0.5 and 5 Pa) have been measured. A simplified one-dimensional model which incorporates the relevant atomic processes of the problem (charge-exchange, lateral diffusion loses, electron impact ionization, and dissociative recombination) is developed. This model allows calculating densities and drift velocities of the different species and, in particular, predicts the creation of a considerable number of metallic neutrals and gaseous ions. A comparison of the experimental ion saturation probe current and the heat source term derived from the calorimetric measurements with the corresponding quantities predicted by the model is performed. We found good agreement between theory and experiment, notwithstanding the fact that the physical quantities presented large variations, and the atomic reaction rates varied for several orders of magnitude, over the range of gas pressure and axial position values investigated. (C) 2001 American Institute of Physics.