Influence of Lyman-series fine-structure opacity on theK-shell spectrum and level populations of low-to-medium-Zplasmas

As laboratory plasmas of increasing atomic number, temperature, size, and/or density are produced, it becomes likely that the details of the doublet opacity profiles of the Lyman series will influence the $K$-shell level populations and spectrum. Accordingly, we have analyzed these effects for a range of plasma parameters, confined to densities low enough for Stark broadening to be unimportant. An analytic model is developed which predicts line power enhancements and level-population changes for $K$-shell plasmas. This model is based upon photon escape probability and collisional quenching concepts and is valid for plasmas of atomic number ∼13-26. Additionally, an extensive set of numerical calculations of line ratios, line profiles, and level populations has been carried out for $K$-shell argon plasmas. Each computation was performed both with detailed fine-structure opacity profiles and with a single-Voigt-profile approximation. The results of these calculations may be scaled for plasmas of atomic number other than 18 using a simple set of rules discussed in the text.