A self-consistent joint description of free and weakly bound electron states in strongly coupled plasmas is presented. The existence of two problems is emphasized. The first one is a well-known restriction of the number of atomic excited states. Another one is a description of the smooth crossover from bound pair electron-ion excited states to collective excitations of free electrons. The fluctuation approach is developed to study the spectrum domain intermediate between low-lying excited atoms and free electron continuous energy levels. The molecular dynamics method is applied to study the plasma model since the method is able to distinguish all kinds of fluctuations. The electronion interaction is described by the temperature-independent cutoff Coulomb potential. The diagnostics of pair electron-ion fluctuations is developed. The concept of pair fluctuations elucidates the smooth vanishing of atomic states near the ionization limit. The approach suggested removes the artificial break of the electron state density at the ionization limit: atomic state density divergent at the negative energy side and free electron state density starting from zero density at the positive energy side.

A plasma model of relaxation of a medium in heavy-ion tracks in condensed matter is proposed. The model is based on three assumptions: the Maxwell distribution of plasma electrons, localization of plasma inside the track nanochannel, and constant values of the plasma electron density and temperature during the x-ray irradiation. The model of multiple ionization of target atoms by a fast projectile ion is used to determine the initial conditions. An analysis of the results of the calculations performed makes it possible to define when the atomic relaxation model is a very rough approximation and the plasma relaxation model must be used. It is demonstrated that the plasma relaxation model adequately describes the x-ray spectra observed upon interaction of a fast ion with condensed target. The comparison with the experimental data justifies the reliability of the plasma relaxation model. Preassumptions of plasma relaxation model are validated by the molecular-dynamics simulation. An x-ray spectral method based on the plasma relaxation model is proposed for diagnostics of the plasma in fast ion tracks. The results obtained can be useful in examining the initial stage of defect formation in solids under irradiation with single fast heavy ions.

A self-consistent fluctuation approach is developed to the consideration of the spectral region intermediate between discrete and continuous levels of energy in nonideal plasma. Pair fluctuations are identified within the classical method of molecular dynamics. The transition of pair fluctuations in the limit of low degrees of nonideality of plasma to excited atoms is considered. The domains of existence of excited atoms and pair fluctuations are estimated. The pattern of restraint of statistical sum of atom in nonideal plasma is clarified.

The molecular dynamics model of collisional recombination in strongly coupled plasmas is developed in the frames of the fluctuation approach. A non-monotonic nonideality dependence of the collisional recombination rate is discovered for all multiplicities of ionization studied. The rate is drastically suppressed with respect to the extrapolation of the ideal plasma three-body recombination conventional expression. The mechanisms of the suppression are discussed. The value of the suppression agrees with the value which was measured for the ultracold plasma. Collisional recombination reduces to the three-body recombination at the decrease of the nonideality.