Enhancement of effective excitation rate coefficients of ions in dense plasma through doubly excited states

We constructed a collisional-radiative model including doubly excited states for a two electron ion. We study the density effects on the effective rate coefficients and the n-dependence of the population densities where n is the principal quantum number. The effective 1s-2l excitation rate coefficients increase with increasing electron density due to the indirect process. We also found that for 2s-1s de-excitation, l-changing transitions, 2snl-2pnl, are important at intermediate densities. The population densities per statistical weight for doubly excited states attain a scale of n-4 at very high density in ionizing plasmas. (author)