SPECTRAL CHARACTERISTICS OF A LOW DENSITY ARC-HEATED NITROGEN PLASMA
ARO INC ARNOLD AFS TN
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The visible and near ultraviolet spectrum from free jets of nitrogen plasmas produced by an arc-jet and exhausted into a low pressure approx torr test cell was photographed under varying conditions. The spectral characteristics were compared to the spectra obtained from argon plasmas produced in the same apparatus. The characteristics of the argon spectra have been attributed to the existence of long-lived, metastable argon atoms the nitrogen spectral characteristics were found to be interpretable in a similar way. The spectrum consisted of N sub 2 first negative and N sub 2 second positive band systems, N atomic lines, and strong impurity radiation from OH, NH, and NO. The impurity bands can be explained on the basis of the ambient test cell gases which mix in the jet boundary and become excited by collision of the second kind with nitrogen atomic and molecular metastables. Several gases, chiefly argon, were mixed with the nitrogen in order to investigate the possible collisions of the second kind and thus determine the mechanisms responsible for the radiation. Several possible mechanisms are proposed in the report, but complete explanation must await further studcy.
- Plasma Physics and Magnetohydrodynamics