Numerical Study of Spectral Line Shapes in High-Density He Plasmas

Abstract

In order to determine the densities and temperatures in high-density helium plasmas by emission spectroscopy, a numerical study of He I spectral line shapes have been performed taking into account radiation trapping. A computational simulation code has been developed, consisting of two parts. The first part solves coupled rate equations to obtain population densities in each energy level of the He atom. The other describes the absorption rate, emission rate, and spectral line shapes by solving the equation of radiation transfer. In a homogeneous plasma, the calculated line profile has a central dip caused by photoabsorption by residual cold atoms. In addition, the results show that radiation trapping significantly alters the population dynamics. The population densities estimated from the intensity of the line profile considering the photoabsorption are lower by one order of magnitude than those without the photoabsorption. For application to a He arc plasma, the temporal evolution of this central dip is also examined as a preliminary calculation.