Molecular dynamics simulations of temperature equilibration in dense hydrogen

Abstract

The temperature equilibration rate between electrons and protons in dense hydrogen has been calculated with molecular dynamics simulations for temperatures between 10 and 600eV and densities between 10;{20}cm;{-3}to10;{24}cm;{-3} . Careful attention has been devoted to convergence of the simulations, including the role of semiclassical potentials. We find that for Coulomb logarithms L greater, similar1 , a model by Gericke-Murillo-Schlanges (GMS) [D. O. Gericke, Phys. Rev. E 65, 036418 (2002)] based on a T -matrix method and the approach by Brown-Preston-Singleton [L. S. Brown, Phys. Rep. 410, 237 (2005)] agrees with the simulation data to within the error bars of the simulation. For smaller Coulomb logarithms, the GMS model is consistent with the simulation results. Landau-Spitzer models are consistent with the simulation data for L>4 .

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

“…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.…”

“…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]. 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].…”

“…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]).…”

“…[23] is particularly notable for its accuracy in this regard, but its application in ICF simulations [24] incurs significant computational expense relative to the simpler theories which neglect CMs such as Landau-Spitzer and its many variants [12,13,15].…”

“…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…”