Towards a general collisional radiative model

Collisional Radiative Models (CRMs) are a widely used tool in the modelling of plasmas. The results of such models appear as source terms in the particle and energy balances of plasma transport models. In case the change of internal energy of the heavy particle is due to electron collisions and radiative processes the Atomic State Distribution Function (ASDF) can be calculated from plasma parameters, such as the electron density and temperature, solving a set of continuity equations. If the electron density is low only a few excited levels have to be taken into account. This holds for, for example, the modelling of conventional fluorescent lamps where, due to an electron density of around 51017 m-3, a model with only four to six excited atomic mercury levels already gives an accurate description of the discharge (Waymouth, 1971). If the electron density rises more levels must be taken into account. This is necessary because of the onset of the stepwise excitation and ionization processes (van Mullen, 1990). If one would use a purely numerical technique all the levels which are not in partial Local Saha Equilibrium (pLSE) (van Mullen, 1990)] have to be taken into account. Fortunately it is possible to reduce the number of levels that need to be treated numerically by using a so-called Analytical Top Model (ATM) for the densities of the higher excited states