Diagnostic of Ar-CO2 mixture plasma using a fine-structure resolved collisional radiative model

Abstract

In the present work, we develop a collisional radiative (CR) model for the Ar-CO2 mixture plasma. The model is applied to the diagnostics of a recently reported low-pressure DC generated Ar-CO2 plasma of Rodríguez et al. [Phys. Plasmas 25, 053512 (2018)] utilizing their spectroscopic measurements who reported the plasma parameters at different concentrations of CO2 in Ar at various pressures and powers. Our CR model includes various population transfer mechanisms between the fine structure levels, viz., electron-impact excitation, radiative decay, and ionization, as well as their reverse processes, e.g., electron-impact de-excitation as well as two- and three-body recombination. The effects of radiation trapping and diffusion are also taken into account. The plasma parameters viz. electron density (ne) and electron temperature (Te) are obtained as a function of different pressures (0.2, 0.3, and 0.6 mbars) and discharge powers at 25 and 50% concentrations of CO2 in argon. These results are determined using measured intensities of seven intense emission lines out of 3p54p (2pi) → 3p54s (1si) fine-structure transitions. It is observed that both the electron density and electron temperature increase with the increase of CO2 concentration, which is in confirmation with experimental predictions. The populations obtained for 1si and 2pi levels from our CR model are also reported and compared respectively with the corresponding available values from the simple CR model and experiment of Rodríguez et al. [Phys. Plasmas 25, 053512 (2018)]. A significant difference in the populations is observed from the two models.