An overview of the ion dynamic effect in line broadening, and a generalization of the unified theory

Abstract

We present a brief overview of the collisional broadening of hydrogenic radiators in thermal plasmas. Our focus is on lines with unshifted central components, particularly the alpha lines (Δ n = 1), for which ion motion effects can be very large. Our calculations span a wide range of electron densities, temperatures, and radiator-ion perturber reduced masses μ. At fixed density and temperature, the ion dynamics will be quasistatic for large μ and impact in nature for sufficiently small μ. The half width, Δω 1 2 , increases with μ in the impact region, and decreases with μ as the quasistatic region is approached. In between these two regions, Δω 1 2 reaches an extrenum where it is relatively insensitive to μ. In this region, the width of L α is a factor more than 30 larger than the value obtained assuming quasistatic ions. We present validity criteria for the different regions of ion dynamic behavior. The above computations were made using a numerical simulation approach. Numerical methods have proven necessary to deal with the overlapping strong collisions of different ion perturbers. Most current analytical methods, such as the unified theory, are not valid when strong collisions overlap, as is often the case with ion perturbers. We are developing a generalization of the unified theory which endeavors to overcome this limitation.