Kinetics of the Population of Atomic Levels in Plasmas

Abstract

The kinetics of the local population of atomic states (p) of ions of charge (z) in plasmas is governed by coupled rate equations of the type $\${\textbackslash}frac{\{{\textbackslash}rm d} n_z {\textbackslash}left(p{\textbackslash}right)}{\{{\textbackslash}rm d}t} = - R_z {\textbackslash}left(p{\textbackslash}to {\textbackslash}right) + R_z {\textbackslash}left({\textbackslash}to p{\textbackslash}right) + {\textbackslash}Gamma_z {\textbackslash}left(p{\textbackslash}right),$$ (8.1) where R z (p→) and R z (→ p) represent the sums of all rates of possible radiative and collisional transitions out of the level (p) and into the level, respectively, and Γ z (p) is the external flux of level-p population by diffusion and convection. It is obvious, that a general solution is practically impossible not only because of the large number of transitions which have to be considered but also for the fact that for many transitions the probabilities and rate coefficients are not known with sufficient accuracy. It is therefore a common approach to reduce the number of rate equations to a set of tractable size by taking into account only the most relevant processes and by considering the pertinent time scales. These so-called collisional-radiative models may differ for different atomic and ionic species and certainly for molecules, and they depend on the regime of plasma parameters.