Modeling and measurements of the arc plasma in a mixture of gases

The wall-stabilized arc is a useful source of the radiation emitted by excited atoms and ions. This plasma has been widely applied in the spectroscopic research, e. g. for measurements of atomic and ionic structure data, such as spectral line strengths or Stark shifts and widths. The wall-stabilized arc and similar plasma sources are also used in many other industrial and scientific applications - especially as the plasma generators in various plasma torches and jets. In most of the applications the plasma is generated in a mixture of gases. As the wall-stabilized cascade arc exhibits the rather strong temperature gradients, the diffusion effects due to the temperature and molar gradients (in the cases of the molecular gases) are prominent, and strongly affect the arc parameters. In this work we present the comparison of the results of the measurements of the plasma parameters in the wall-stabilized arc working in the mixture of argon and nitrogen with the theoretical calculations of the plasma temperatures and molar ratios. The gas mixture is introduced uniformly along the arc column between each of the stabilizing plates. From measured lateral distribution of radiation (NI, HI, ArI line intensity and width measurements), after Abel inversion the radial temperature and species distributions were obtained at various positions of the arc column. As the atomic lines can be measured only close to the plasma axis (the Boltzmann plot of the atomic argon or nitrogen lines is reliable only if the sufficiently highly excited states are present), for the measurement of the fringe temperatures the molecular spectroscopy was also performed (measurements of the bands of nitrogen molecule and nitrogen molecular ion). The model consisted of one-dimensional calculations of all plasma parameters (both temperature and demixing), based on the theory developed by Murphy. The results show that even the relatively simple model can predict the molecular ratio distributions in the gas mixtures and its dependence on the initial gas flow ratios. (author)