Molecular-dynamics simulations are used to investigate temperature relaxation between electrons and ions in a fully ionized, classical Coulomb plasma with minimal assumptions. Recombination is avoided by using like charges. The relaxation rate agrees with theory in the weak coupling limit (g identical with potential/kinetic energy << 1), whereas it saturates at g > 1 due to correlation effects. The "Coulomb log" is found to be independent of the ion charge (at constant g) and mass ratio > 25.

A plasma transport theory that spans weak to strong coupling is developed from a binary collision picture, but where the interaction potential is taken to be an effective potential that includes correlation effects and screening self-consistently. This physically motivated approach provides a practical model for evaluating transport coefficients across coupling regimes. The theory is shown to compare well with classical molecular dynamics simulations of temperature relaxation in electronion plasmas, as well as simulations and experiments of self-diffusion in one component plasmas. The approach is versatile and can be applied to other transport coefficients as well.PACS numbers: 52.25. Fi,52.27.Gr,52.65.Yy The microscopic dynamics of Coulomb collisions determines macroscopic transport properties of plasmas such as diffusivity, resistivity, viscosity, etc. [1,2]. Usually plasmas are so hot and dilute that the average particle kinetic energy greatly exceeds the potential energy of interaction. In this weakly coupled regime, Coulomb collisions consist of a series of many small angle binary scattering events [3][4][5][6]. Strongly coupled plasmas are fundamentally different. In this regime, the interaction potential energy exceeds the particle kinetic energies, so scattering angles are large and correlation effects are important. Plasmas in several modern experiments, including inertial confinement fusion (ICF) [7,8], antimatter plasmas [9], ultra cold plasmas [10] and dusty plasmas [11], exhibit strong coupling effects; as do some naturally occurring objects including neutron star crusts [12], white dwarf stars [13,14] and giant planet interiors [15][16][17].Understanding how transport properties are modified in strongly coupled plasmas is interesting both from a fundamental physics standpoint and as a practical matter. Accounting for correlation effects remains a challenge for theory, even though accurate transport coefficients are critical input to the macroscopic (fluid) equations used to model these systems. Transport calculations typically rely on computationally expensive particle simulations, such as molecular dynamics (MD) [18][19][20]. Analytic theory is desirable because it can both elucidate the physical processes that influence transport at strong coupling, and provide an efficient means for estimating the transport coefficients that fluid equations require as input [21][22][23]. In this Letter, we describe a physically motivated method of extending conventional transport calculations, which is efficient enough to be practically implemented in fluid simulation codes. The theory provides coefficients that agree with experimental [24] and classical MD simulation data [25,26] across coupling regimes.Like weakly coupled theories, our theory is based on a binary collision picture, but where particles interact via an effective potential that includes average effects of the intervening medium; including both correlations and screening. This effective potential is used to derive a scattering cross section, wh...

We present a model for the rate of temperature relaxation between electrons and ions in plasmas. The model includes self-consistently the effects of particle screening, electron degeneracy and correlations between electrons and ions. We successfully validate the model over a wide range of plasma coupling against molecular-dynamics simulations of classical plasma of like-charged electrons and ions. We present calculations of the relaxation rates in dense hydrogen and show that, while electron-ion correlation effects are indispensable in classical, like-charged plasmas at any density and temperature, quantum diffraction effects prevail over e-i correlation effects in dense hydrogen plasmas.

A method for extending traditional plasma transport theories into the strong coupling regime is presented. Like traditional theories, this is based on a binary scattering approximation, but where physics associated with many body correlations is included through the use of an effective interaction potential. The latter is simply related to the pair-distribution function. Modeling many body effects in this manner can extend traditional plasma theory to orders of magnitude stronger coupling. Theoretical predictions are tested against molecular dynamics simulations for electron-ion temperature relaxation as well as diffusion in one component systems. Emphasis is placed on the connection with traditional plasma theory, where it is stressed that the effective potential concept has precedence through the manner in which screening is imposed. The extension to strong coupling requires accounting for correlations in addition to screening. Limitations of this approach in the presence of strong caging is also discussed.

Molecular dynamics simulations are used to investigate the diffusion properties of one-component plasmas and binary ionic mixtures from the weakly to the strongly coupled regimes. A physically motivated model for the diffusivities is proposed that reproduces the simulation data and gives insight into the nature of ionic motions and interactions in plasmas across the coupling regimes. The model extends the widely used Chapman-Spitzer theory from the weakly to the moderately coupled regime. In the strongly coupled regime, diffusion is modeled in terms of thermally activated jumps between equilibrium positions separated by an energy barrier. The basic ideas discussed are applicable to the study of other transport coefficients.