Microfield dynamics in dense hydrogen plasmas with high-Zimpurities

Abstract

We use large-scale classical molecular dynamics to determine microfield properties for several dense plasma mixtures. By employing quantum statistical potentials (QSPs) to regularize the Coulomb interaction, our simulations follow motions of electrons as well as ions for times long enough to track relaxation phenomena involving both types of particles. Coulomb coupling, relative to temperature, of different pairs of species in the hot, dense matter being simulated ranges from weak to strong. We first study the effect of such coupling differences, along with composition and QSP differences, on the roles of electrons and various mixture components in determining probability distributions of instantaneous, total microfields experienced by the ions. Then, we address two important dynamical questions: (1) how is the quasi-static part of the total field to be extracted from the timedependent simulation data; and, (2) under what conditions does the commonly used approximation of ions with fixed Yukawa-like screening by free electrons accurately describe quasi-static fields? We identify a running, short-time average of the total field at each ion as its slowly evolving, quasi-static part. We consider several ways to specify the averaging interval, and note the influence of ion dynamics in this issue. When all species are weakly coupled, the quasi-static fields have probability distributions agreeing well with those we obtain from simulations of Yukawa-screened ions. However, agreement deteriorates as the coupling between high-Z ions increases well beyond unity, principally because the Yukawa model tends to underestimate the true screening of close high-Z pairs. Examples of this fact are given, and some consequences for the high-field portions of probability distributions are discussed.

A drift of Langmuir waves in a magnetized inhomogeneous plasma

“…(2012, 2016), Ziebell et al. (2012), Plunk (2013), Wang (2013), Hau-Riege & Weisheit (2017), Rozmus et al. (2017), Shi, Qin & Fisch (2017), Belyi (2018) and Schoeffler, Loureiro & Silva (2018).…”

Classical molecular dynamics simulations of hydrogen plasmas and development of an analytical statistical model for computational validity assessment

“…While QSPs' behavior at short distances typically depends on plasma temperature through the thermal de Broglie wavelength, the latter one is designed to match the corresponding ionization energy at the origin. The impact of using different types of potentials on statistical properties of dense hydrogen plasmas with impurities has been recently studied [24,25]. Neglecting the ionization-recombination mechanism, these works suggest that slow electric microfield distributions are rather insensitive to the potential alternatives and, therefore, such choice would have a small impact on the calculation of Stark-broadened line profiles.…”

“…On the upside, however, collective behaviors (e.g., ion dynamic effects) emerge in a natural way, the range of validity extends to strongly coupled plasmas and, with the lack of experimental data, MD results are often considered as a reference to reveal model deficiencies and provide valuable guidance for theory improvement. Classical MD simulations have been applied to the study of diverse statistical properties, particle correlation effects, and in particular to the investigation of plasma electric microfield distributions [17][18][19][20][21][22][23][24][25]. Although mainly performed in the context of fully ionized two-component plasmas, all this work enabled the study of electric microfield issues beyond the capability of most theoretical methods.…”