Collisionalradiative

Collisional-radiative modeling refers to a framework used in plasma physics to describe the populations of atomic and ionic energy levels under non-equilibrium conditions by balancing collisional and radiative processes. A collisional-radiative (CR) model treats each element as a set of ionization stages and excited levels, and determines their populations by solving coupled rate equations that account for electron-impact excitation and de-excitation, electron-impact ionization, three-body recombination, radiative recombination, dielectronic recombination, and spontaneous radiative decay. When present, radiation fields can also drive photoexcitation and photoionization, and, in some cases, collisional interactions with ions other than electrons may be included.

Inputs to a CR model include the electron temperature and density, elemental abundances, and a database of atomic data such as energy levels and transition rates. The model can be time-dependent, yielding the evolution of level populations and ionization balance, or steady-state, where production and loss rates are balanced (dN/dt = 0). From the computed level populations and ion fractions, one can predict emitted spectra and line intensities, allowing CR models to serve as tools for diagnostic of plasma conditions.

CR modeling is widely used in laboratory plasmas, such as laser-produced and pulsed-power plasmas, as well as in astrophysical contexts like stellar coronae and supernova remnants, and in fusion devices. Limitations include reliance on comprehensive and accurate atomic data and the need to account for radiative transfer effects in optically thick media, which may require coupling to separate radiation transport calculations.