First principles nonequilibrium plasma mixing

Abstract

We have performed nonequilibrium classical and quantum-mechanical molecular dynamics simulations that follow the interpenetration of deuterium-tritium (DT) and carbon (C) components through an interface initially in hydrostatic and thermal equilibrium. We concentrate on the warm, dense matter regime with initial densities of 2.5-5.5 g/cm3 and temperatures from 10 to 100 eV. The classical treatment employs a Yukawa pair-potential with the parameters adjusted to the plasma conditions, and the quantum treatment rests on an orbital-free density functional theory at the Thomas-Fermi-Dirac level. For times greater than about a picosecond, the component concentrations evolve in accordance with Fick's law for a classically diffusing fluid with the motion, though, described by the mutual diffusion coefficient of the mixed system rather than the self-diffusion of the individual components. For shorter times, microscopic processes control the clearly non-Fickian dynamics and require a detailed representation of the electron probability density in space and time.

Cooking strongly coupled plasmas

“…A particularly interesting feature is the possibility to perform direct simulations of mixtures such as deuterium-tritium, hydrogen-iron, deuterium-carbon, deuterium-tritium-carbon, lithium-hydride, lithiumdeuteride [29][30][31][32][33][34][35], etc. to check the validity of mixture rules for thermodynamical [30] and transport properties [36].…”

Molecular Dynamics Simulations of Warm Dense Carbon

“…We note that, while some studies have used a specific definition to compute Z from DFT calculations, [12,24] the definition of Z is somewhat complicated since it requires one to make some assumptions regarding how to differentiate between "free" vs. "bound" electrons. In this study, the DFT-MD calculations are expected to give the best description of the electronic structure at these conditions.…”

“…Convergence of the EOS with respect to simulation size requires a modest number of C atoms (∼10s -100s, depending on density and temperature) in a periodically repeated box. Recent calculations of interspecies mixing at C/DT (50-50 mixture of deuterium and tritium) interfaces [12] use both orbital-free DFT (a more approximate variant of DFT neglecting atomic shell structure) and simple Yukawa pair potentials. Those approaches were chosen to enable the much larger simulation boxes (1000s of atoms) needed to produce accurate descriptions of the time-evolving material interface.…”

Transport properties of an asymmetric mixture in the dense plasma regime

“…We will perform simulations along isobars-isotherms and look at the impact of varying concentration at several different temperatures, and we systematically study the evolution of the ionic transport properties. We imagine an interface at pressure and temperature equilibrium [33,34] and sample different concentrations between pure H and Ag. The density varies from pure Ag at 20 g/cc to pure H. The density of the H depends on the temperature (0.8-3.8 g/cc).…”