Molecular-Dynamics Simulations of Electron-Ion Temperature Relaxation in a Classical Coulomb Plasma

Abstract

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.

Molecular dynamics studies of electron-ion temperature equilibration in hydrogen plasmas within the coupled-mode regime

“…(dT e /dt = −dT i /dt) were noted in earlier work on hydrogen plasmas [8,9,[11][12][13]. In our cases here, however, the ions are sufficiently cold that such an asymmetric temperature relax-ation is expected [7,21,23].…”

“…For the classical like-charge proton-positron system, demonstration of agreement was somewhat more straightforward, motivating a clear connection between the classic LandauSpitzer equilibration rate [15] derived from the Fokker-Planck equation, and a generalized Lenard-Balescu [16] scheme in which both dynamical screening and 2-body static correlations (in the form of local field corrections) are included [8]. Furthermore, it was shown that for many regimes of interest to ICF, the complex dynamical screening of the 2-component (electron + proton) plasma could be replaced by the static response of the electrons alone, yielding identical results [8,9,12,13]. This is hardly surprising, since in a given electronproton collision, the "spectator" electrons are expected to move much faster than the much heavier "spectator" protons.…”

“…Recent work on T -equilibration has involved both kinetic theory of various types [4][5][6][7][8], and MD simulations with like-charges and the pure Coulomb interaction [8,9] as well as opposite-charge simulations with quantum statistical potentials (QSPs) to mock up the effects of quantum diffraction [10][11][12][13][14]. All but a few of these studies [7,11,14] confined themselves to pure hydrogen (or the proton-positron system [8,9]).…”

“…All but a few of these studies [7,11,14] confined themselves to pure hydrogen (or the proton-positron system [8,9]). Even for H, the demonstration of agreement between MD results and kinetic theory took some time [10][11][12][13], in part because the effect of using the QSPs changes the result slightly even in weak coupling [11].…”

“…To this end, Vorberger and Gericke searched through the existing MD results [8,9,[11][12][13][14]25] to assess if simulations within the regime of interest for…”