A hybrid method for investigating the detailed emission spectra of mid-Z plasmas in non-local thermodynamic equilibrium: Ge as an example

The detailed radiative properties of plasmas in non-local thermodynamic equilibrium (NLTE) are important for determining experimental plasma states. However, a complete detailed-level-accounting approach calculation is impractical for mid- and high-Z elements. Herein, we propose a hybrid method for obtaining the detailed radiative properties of mid-Z NLTE plasmas. First, a large-scale rate equation within the framework of a detailed-configuration-accounting method is established using atomic data in a configuration-configuration formalism. Second, we assume that the population distributions in fine-structure levels belonging to a particular configuration are in equilibrium. Thus, the populations at fine-structure levels are obtained through the populations in the corresponding configurations. Finally, detailed radiative properties are calculated using the populations in fine-structure levels and radiative data in level-level formalism. Such a method can balance computation costs and accuracy. Examples utilizing Ge plasmas demonstrate that the proposed method can better predict detailed structures in emission spectra than the detailed-configuration-accounting method.