Ionic excitation in dense, two-component plasmas: A nonperturbative approach

A nonperturbative formulation of atomic collisional excitation rates in dense plasmas is developed on the basis of the equations of motion for density matrices in a stochastic potential. This model treats the strong scattering between the atom and plasma particles through the many-body correlation functions describing plasma density fluctuations, which are decomposed into the products of dynamic structure factors within the decorrelation approximation and then are summed to infinite order. A simple analytic solution to the density matrix equation is obtained for two-level atoms. The electron-induced transition of a hydrogen-like ion in dense hydrogen plasma is studied as an example. It is demonstrated that, when the plasma density is sufficiently high, low-frequency ion-density fluctuations influence the electron dynamics and thereby cause coherent excitation between close-lying atomic states. The resultant time evolution of the atomic level population differs considerably from the prediction of one-component plasma collisional rate equations based on first-order perturbation theory (Born approximation). (C) 2000 American Institute of Physics. [S1070-664X(00)02508-8].