Collisional-radiative model

A collisional-radiative model solves coupled atomic population equations using collisions, radiative transitions, ionization and recombination. For one fixed ion stage, a common stationary approximation is $0={\sum }_{j\ne i}(n_j{P}_{ji}-n_i{P}_{ij})$, supplemented by the total ion population. Electron-impact rates contribute $n_e{q}_{ij}(T)$ and spontaneous downward transitions contribute $A_{ij}$. Additional radiation, proton collisions and adjacent-ion source terms are included when significant.