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 operate d with oxygen gas at a constant current level of 100 A has been investigate d by employing a Langmuir spherical probe and a calorimetric technique. The plasma potential and electron temperature at several axial distances (betw een 10 and 25 cm) from the cathode surface and for different O-2 pressure v alues (between 0.5 and 5 Pa) have been measured. A simplified one-dimension al model which incorporates the relevant atomic processes of the problem (c harge-exchange, lateral diffusion loses, electron impact ionization, and di ssociative recombination) is developed. This model allows calculating densi ties and drift velocities of the different species and, in particular, pred icts the creation of a considerable number of metallic neutrals and gaseous ions. A comparison of the experimental ion saturation probe current and th e heat source term derived from the calorimetric measurements with the corr esponding quantities predicted by the model is performed. We found good agr eement between theory and experiment, notwithstanding the fact that the phy sical 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.