Electron Density Measurements of Shocked Argon Using Stark Profile of the H Line

Abstract

Electron density measurements are conducted using a free-piston shock tube to investigate the nonequilibrium ionization process of shocked argon. The H line of hydrogen is observed using the spatially resolved emission spectroscopy, and the electron density is evaluated by a profile matching of the Stark broadened H line. The experimental results are compared with calculated ones obtained by computational fluid dynamics. The measured electron density shows larger values than the calculated ones by one order of magnitude. The calculated electron density increases until the equilibrium value, showing the difference of the spatial distribution of the electron density between experiment and calculation. Water vapor impurity has a significant effect, which shortens the relaxation distance in the present condition, making the agreement between experiment and calculation better. There is, however, still a discrepancy between experiment and calculation. Precursor phenomena could be a possible reason causing the discrepancy. The modeling and implementation of precursor phenomena are important for future investigations.