Spectroscopic investigations on impurities and their effect on the electron number density in the shock tube

An accurate estimation of electron number density is significant in many plasma physics studies. In this paper, the effect of impurities in test gas on the electron number density of the plasma generated in the hypersonic flow of a free-piston driven hypersonic shock tube has been studied using optical emission spectroscopy. Emission spectra of argon plasma showed the presence of following impurities: sodium, potassium, nitrogen, oxygen and hydrogen. The electron number density calculated from the spectral broadening of argon emission lines, is one order of magnitude higher than the electron number density calculated from the thermochemical equilibrium flow model that does not include the impurities. Hence the results show that the presence of impurities has a significant impact on the shock tube plasma and warrants the need to include these effects in the thermochemical equilibrium flow model while investigating magneto-aerodynamic interaction flows and communication blackout studies in the hypersonic ground-based test facilities.