Draft:Collisional-Radiative Modeling

Collisional-radiative modeling is used to calculate quantum state densities and the emission/absorption properties of a plasma. It is one of the most general approaches and lies between the extrema of a local thermal equilibrium and a coronal picture. In a local thermal equilibrium the population of excited states is distributed according to a Boltzmann distribution. However, this holds only if densities are high enough for an excited hydrogen atom to undergo many collisions such that the energy is distributed before the radiative process sets in. In a coronal picture the timescale of the radiative process is small compared to the collisions since densities are very small.

The coronal picture should not be confused with a coronal equilibrium. A coronal equilibrium is the non-transport ionization balance of recombination and ionization. The only thing they have in common is that they are not valid in nowadays tokamaks.