Quantum Atomic Population Kinetics in Dense Plasmas

The atomic populations are the fundamental quantities for various different disciplines in science and applications. Although the rate equation model has widely been employed, it has principal deficiencies as it considers only populations related to the squared of the wave functions, while all mixed populations (coherences) are missing. In plasmas, however, large effects of strong plasma electric microfields on atomic (usually highly charged ions) energy levels are encountered that require more advanced descriptions, e.g., energy level evolution under the action of a quasi-static electric ion field including coherence effects. For real systems, these phenomena cannot be described consistently in the framework of the Schrödinger picture but request the density matrix description in contrast to the standard population balance rate equations. The general system of density matrix equations, however, is extremely challenging. It is demonstrated that the system can be transformed to a standard form of population kinetic rate equations with additional terms describing the effect of the ion electric field, the so-called quantum F-matrix theory (QFMT) allowing to construct real (large) closed model systems. The density matrix approach results in a new understanding of the fundamental physical problem connected with the transition of atomic populations to the Boltzmann equilibrium in dense plasmas. The standard transition is provided by electron collisions only satisfying the principle of detailed balance related to a statistical population of energy levels over magnetic quantum numbers. However, the effect of static electric fields on the atomic population is selective in magnetic quantum numbers resulting in a destruction of statistical Boltzmann populations. The interplay between the statistical effect of electrons and non-statistical effect of quasi-static ions is illustrated in detail for autoionizing atomic states of highly charged ions in dense laser-produced plasmas.