Spectroscopic Analysis of Titan Atmospheric Plasmas

摘要

The analysis of emission spectroscopy measurements performed on plasmas with a composition representative of the atmosphere of Titan is presented. The plasmas are produced in the von Karman Institute for Fluid Dynamics Minitorch inductively coupled plasma wind tunnel. Absolute volume emissivities are obtained for two different test conditions. The first one, a high-pressure test condition, is selected to obtain conditions close to local thermodynamic equilibrium. The second one, a low-pressure test condition, is selected to investigate possible departure from equilibrium conditions. The analysis of the measured spectra is performed with a radiation code developed at the von Karman Institute for Fluid Dynamics for this purpose. Dynamic behavior of the plasma jet is considered and the effect of observed fluctuations is included in the analysis. An estimated radial distribution of the error induced by the fluctuations on the measured volume emissivity is computed. Good agreement between measurement and computation is obtained for the high-pressure test condition at the center of the jet. For larger radial positions the error induced by the fluctuations increases and greater corrections have to be applied. A preliminary analysis of the low-pressure test condition at the center of the jet leads to the introduction of large overpopulation factors attributed to the emitting vibrational and electronic energy levels.