Measurement of Stark width of some Ar I transitions and the investigation of local thermodynamic equilibrium (LTE) in an atmospheric d.c. argon plasma jet

The Stark widths of seven Ar I transitions are reported. Axial line shape data from an atmospheric d.c. argon plasma jet were Abel-inverted to obtain radial line shapes. The electron-density was determined by Stark width measurements of the hydrogen H{dollar}sbbeta{dollar} transition. In the electron-density region of {dollar}leq{dollar}6 {dollar}times{dollar} 10{dollar}sp{lcub}22{rcub}{dollar} m{dollar}sp{lcub}-3{rcub}{dollar} the experimental Ar I Stark widths are fitted to a linear dependence on the electron-density. Values of Stark width extrapolated to other electron-densities are compared to measurements reported in the literature on the 4s-4p array. Experimental values are up to 45% smaller than those predicted by Griem's theory of Stark broadening. The experimental values of the electron-impact parameter W are reported.; An investigation has been made of the conditions for local thermodynamic equilibrium (LTE) to exist in an atmospheric argon plasma jet. The experiment measures the emission coefficient of seven Ar I transitions and the line shape of the hydrogen H{dollar}sbbeta{dollar} transition. After transforming the side-on data into radial space the excited neutral argon atom-density and the electron-density are determined. It is found LTE does not exist below an electron-density of 6 {dollar}times{dollar} 10{dollar}sp{lcub}33{rcub}{dollar} m{dollar}sp{lcub}-3{rcub}{dollar} in our experimental conditions. The two-temperature Saha equation is shown to give non-physical results for gas temperatures in our electron-density range of 2-6 {dollar}times{dollar} 10{dollar}sp{lcub}22{rcub}{dollar} m{dollar}sp{lcub}-3{rcub}{dollar}. Diffusion effects are important under the experimental conditions studied.