Spectroscopic Temperature Determinations for a Microwave-Induced Helium Plasma Formed in a Laminar Flow Torch

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Abstract
This study represents the first plasma diagnostic investigation of a laminar flow torch configuration for microwave-induced plasma emission spectroscopy. Spatial intensity profiles indicate that this torch design facilitates the formation of a stable plasma discharge which does not reside on the walls of the plasma containment tube. Spectroscopic temperature determinations were based on the assumption of local thermodynamic equilibrium. Excitation temperatures were found to be several thousand degrees higher than those reported for other low-power He plasmas. Rotational temperature determinations afforded bimodal temperature distributions from the Boltzmann plots, with lower temperature slope regions comparable to values reported by others. Rotational temperatures derived from high-temperature slope regions were several thousand degrees above values obtained in other studies. Temperatures were evaluated as a function of radial position, microwave power, and flow rate.