On the frequency of inelastic collisions in a plasma

The effect of polarization plasma phenomena on the frequency of inelastic atomic transitions induced by the combined electron and ion field is considered. The inelastic collision frequency W can be expressed in terms of the Born matrix element and the longitudinal component of the plasma dielectric permeability at the atomic transition frequency ωsub(0)=ΔE/h (ΔE is the transition energy). For a low-density plasma the frequency W is identical with N (vsigmasub(01)), where sigmasub(01) is the effective excitation cross section for the transition averaged over the velocity distribution function of the perturbing charged particles of the plasma and N is the particle density. The dependence of the collision freqeuncy on plasma temperature and density is investigated in detail for optically allowed transitions with a small resonance defect sigma0. It is shown that polarization effects play an important role at temperatures for which the main contribution to the inelastic collision frequency is due to electron - atom collisions. Although inelastic transitions in the plasma may predominantly be due to interaction with ions, the polarization effects are not appreciable up to high densities which are close to those of a solid body. Conditions of applicability of the first order perturbation theory are formulated for an inelastic transition frequency with a small resonance defect