On the Relation Between Diffusion and Shear Viscosity in Two-Dimensional Magnetized Yukawa Liquids
We investigate the interplay between shear viscosity and diffusion in a 2D Yukawa liquid subjected to an external magnetic field.
physics.plasm-ph↗
arXiv subjects
T. S. Ramazanov
Publications and source records attributed to T. S. Ramazanov.
Force Fields for Molecular Dynamics Simulations of Charged Dust Particles with Finite Size in Complex Plasmas
To exclude collisions leading to the overlap of finite-sized charged particles in molecular dynamics (MD) simulations in systems like complex (dusty) plasmas, we developed a scheme to generate a pair interaction force functionally depending on the pair distribution of particles. This ensures that the pair distribution function drops to zero at distances between particles corresponding to the point where the surfaces of two particles come into contact. The presented model has a wide utility for the description of various processes in dusty plasmas. As an example, using the non-equilibrium MD method, we performed calculations of the shear viscosity and thermal conductivity of charged spherical particles interacting via screened Yukawa potential. The role of finite particle size was found to be particularly important for small values of the coupling parameter, i.e., for gas-like and weakly correlated liquid-like systems. Furthermore, we have analyzed the shear viscosity and thermal conductivity in the presence of an external uniform magnetic field.
physics.plasm-ph↗
Impact of the local field correction on transport and dynamic properties of warm dense matter
The plasma screening model, taking into account the electronic exchange-correlation effects and the ionic non-ideality in dense quantum plasmas, is presented. This model can be used as an input in various plasma interaction models to calculate the scattering cross-sections and transport properties. The application of the presented plasma screening model is demonstrated on the example of the temperature relaxation rate in dense hydrogen and warm dense aluminum. Additionally, we compute the conductivity of warm-dense aluminum in the regime where collisions are dominated by electron-ion scattering. The obtained results are compared with available theoretical results and simulation data.
physics.plasm-ph↗
Magnetic Field Induced Ion Trapping Around Dust Particle in Plasma
This paper investigates the binary collision between an ion and a charged dust particle in the plasma in the presence of a uniform magnetic field. The trajectories of ions are calculated using the modified Velocity Verlet algorithm designed for a reliable simulation of the charged particle dynamics in arbitrarily strong static homogeneous external magnetic fields. We consider the coupling parameter values characteristic for dusty plasma experiments and the external magnetic field with $B\leq 1~{\rm T}$. It has been revealed that at some magnetic field values, the ions are trapped around the charged dust particle. The magnetic field strength values in which the ion becomes trapped around the dust particle have been obtained for typical argon and helium gas discharge plasma parameters.
physics.plasm-ph↗
Demarcating the classical and quantum approaches for the Coulomb logarithm in plasmas
The Coulomb logarithm often enters various plasma models and simulation methods for computing the transport and relaxation properties of plasmas. Traditionally, a classical pair collision picture was used to calculate the Coulomb logarithm for different plasma parameters. With the recent emergence of the high interest in dense plasmas with partially degenerate electrons, new approaches have been developed to treat electron-ion collisions in a quantum-mechanical way. In this context, gaining a deeper physical understanding of the criteria for the applicability of classical plasma models is crucial. We have analyzed the Coulomb logarithm describing the electron-ion collisions in hydrogen plasmas in a wide range of temperatures and densities relevant to inertial confinement fusion experiments. The electron-ion collision cross-sections were computed using both quantum and classical scattering theories. We found that the classical description of the electron-ion scattering in plasmas and related plasma models is applicable if the de Broglie wavelength of electrons is smaller than the ion charge screening length in plasmas. Additionally, we show that the quantum first-order Born approximation for describing the electron-ion collision is accurate only in the regime where classical scattering theory is accurate.
physics.plasm-ph↗
Microdischarge dynamics of volume DBD under the natural convection flow
The impact of convective flow due to the temperature gradient between discharge cell electrodes and ambient air was studied for parallel-plate electrode arrangement. It was shown that an increase in temperature during the discharge operation leads to an increase in MD number in the discharge gap. The convective gas flow velocity also increased at a higher thermal gradient, and MD channels follow the gas flow direction. The velocity of convective flow was estimated by the CFD simulation and compared with the mean velocity of MD channels obtained by the particle image velocimetry method.
physics.plasm-ph↗
Shear Viscosity in Two-Dimensional Dipole Systems
The results of modeling shear flows in classical two-dimensional dipole systems are presented. We used the method of non-equilibrium molecular dynamics to calculate the viscosity at various shear rates. The coefficients of shear viscosity are given in the limit of low shear rates for various regimes of interparticle correlation from a weakly correlated gaseous state to a strongly non-ideal liquid state near the crystallization point. The effect of shear thinning in 2D dipole systems is reported at small values of the coupling parameter. In addition, it is shown that dipole systems can become both less and more viscous due to the presence of a screening medium, depending on the degree of interparticle correlation. The optimal simulation parameters are discussed within the framework of the method of nonequilibrium molecular dynamics for determining the shear viscosity of two-dimensional dipole systems. Moreover, we present a simple fitting curve which provides universal scaling law for both bare dipole-dipole interaction and screened dipole-dipole interaction.
physics.plasm-ph↗
Ion core effect on transport characteristics in warm dense matter
An effective potential approach in combination with the molecular dynamics (MD) method was used to study the effect of the ionic core on the transport properties of ions in the warm dense matter regime. As an example, we considered shocked silicon. The results of MD simulations within microcanonical ensemble were analyzed by computing the mean squared displacement (MSD) and the velocity autocorrelation function (VAF) of particles. The MSD and VAF are used to compute the diffusion coefficient of ions. The results are compared with the data computed neglecting the ion core effect. It is found that the ion core effect leads to a significant decrease of the diffusion coefficient. Additionally, we computed the viscosity coefficient of ions using the Green-Kubo relation connecting viscosity and the stress autocorrelation function. It is revealed that the ion core effect can cause increase or reduction of the viscosity coefficient depending on the strength of inter-ionic coupling.
physics.plasm-ph↗
Investigation of the influence of single particle oscillations on the transport properties of dense plasma
Transport properties of the ionic component of dense plasmas are investigated on the basis of effective potentials taking into account the presence of an external alternating electrical (laser) field. The latter generates single particle oscillations of electrons and significantly changes the screening of the test charge in plasma. Therefore, transport coefficients become non-monotonic function of the oscillation frequency. The results for the diffusion and viscosity coefficients are presented. These transport coefficients are computed using the generalized Coulomb logarithm within the Chapman-Enskog model for the fluid description. It was revealed that the oscillation of the electrons in the alternating external field in the significant reduction of the ionic diffusion and viscosity coefficients. The ionic diffusion and viscosity coefficients are larger compared to the case without the external field impact.
physics.plasm-ph↗
Surface waves in a collisional quark-gluon plasma
Surface waves propagating in the semi-bounded collisional hot QCD medium (quark-gluon plasma) are considered. To investigate the effect of collisions as damping and non-ideality factor, the longitudinal and transverse dielectric functions of the quark-gluon plasma are used within the Bhatnagar-Gross-Krook (BGK) approach. The results were obtained both analytically and numerically in the long wavelength limit. First of all, collisions lead to smaller values of surface wave frequency and their stronger damping. Secondly, the results show that non-ideality leads to the appearance of a new branch of surface waves compared to the collisionless case. The relevance of the surface excitations (waves) for the QGP realized in experiments is discussed.
physics.plasm-ph↗
Energy loss and friction characteristics of electrons at warm dense matter and non-ideal dense plasma conditions
We investigate the energy loss characteristics of warm dense matter (WDM) and dense plasmas concentrating on the influence of electronic correlations. The basis for our analysis is a recently developed ab initio Quantum Monte-Carlo (QMC) based machine-learning representation of the static local field correction (LFC) [Dornheim et al., J. Chem. Phys. 151, 194104 (2019)], which provides an accurate description of the dynamical density response function of the electron gas at the considered parameters. We focus on the polarization-induced stopping power due to free electrons, the friction function, and the straggling rate. In addition, we compute the friction coefficient which constitutes a key quantity for the adequate Langevin dynamics simulation of ions. Considering typical experimental WDM parameters with partially degenerate electrons, we find that the friction coefficient is of the order of $γ/ω_{pi}=0.01$, where $ω_{pi}$ is the ionic plasma frequency. This analysis is performed by comparing QMC based data to results from the random phase approximation (RPA), the Mermin dielectric function, and the Singwi-Tosi-Land-Sjölander (STLS) approximation. It is revealed that the widely used relaxation time approximation (Mermin dielectric function) has severe limitations regarding the description of the energy loss properties of correlated partially degenerate electrons. Moreover, by comparing QMC based data with the results obtained using STLS, we find that energy loss properties are not sensitive to the inaccuracy of the static LFC at large wave numbers $k/k_{F}>2$ (with $k_F$ being the usual Fermi wave number), but that a correct description of the static LFC at $k/k_{F}\lesssim 1.5$ is important.
physics.plasm-ph↗
Dynamical structure factor of strongly coupled ions in a dense quantum plasma
The dynamical structure factor (DSF) of strongly coupled ions in dense plasmas with partially and strongly degenerate electrons is investigated. The main focus is on the impact of electronic correlations (non-ideality) on the ionic DSF. The latter is computed by carrying out molecular dynamics (MD) simulations with a screened ion-ion interaction potential. The electronic screening is taken into account by invoking the Singwi-Tosi-Land-Sjölander approximation, and compared to the MD simulation data obtained considering the electronic screening in the random phase approximation and using the Yukawa potential. %This allows us to gain insight into the impact of the electronic non-ideality on the ionic DSF. We find that electronic correlations lead to lower values of the ion-acoustic mode frequencies and to an extension of the applicability limit with respect to the wave-number of a hydrodynamic description. Moreover, we show that even in the limit of weak electronic coupling, electronic correlations have a non-negligible impact on the ionic longitudinal sound speed. Additionally, the applicability of the Yukawa potential with an adjustable screening parameter is discussed, which will be of interest, e.g., for the interpretation of experimental results for the ionic DSF of dense plasmas.
physics.plasm-ph↗
A critique of "quantum dusty plasmas"
During the recent decade a steadily increasing number of papers devoted to so-called "quantum dusty plasmas" (QDP) appeared. These systems are combining the properties of dusty (i.e. micrometer to nanometer-sized particles containing) plasmas with quantum effects %(of electrons) appearing at high-density and/or low-temperature. Many exciting properties of QDP were predicted including nontrivial collective oscillations and linear and nonlinear waves. It was predicted that the results have relevance for dense astrophysical plasmas such as white dwarf stars, neutron stars, magnetars and laboratory plasmas in micro- and nano-devices. Here we present a careful examination of the plasma parameters for the expected applications and compare them to the conditions under which a dust particle can exist in a quantum plasma. The conclusion is that quantum dusty plasmas do not exist in reality.
physics.plasm-ph↗
Structural characteristics of strongly coupled ions in a dense quantum plasma
The structural properties of strongly coupled ions in dense plasmas with moderately to strongly degenerate electrons are investigated in the framework of the one-component plasma model of ions interacting through a screened pair interaction potential. Special focus is put on the description of the electronic screening in the Singwi-Tosi-Land-Sjoelander (STLS) approximation. Different crosschecks and analyses using ion potentials obtained from ground-state quantum Monte Carlo data, the random phase approximation (RPA), and existing analytical models are presented for the computation of the structural properties, such as the pair distribution and the static structure factor, of strongly coupled ions. The results are highly sensitive to the features of the screened pair interaction potential. This effect is particularly visible in the static structure factor. The applicability range of the screened potential computed from STLS is identified in terms of density and temperature of the electrons. It is demonstrated that at r_s > 1, where rs is the ratio of the mean inter-electronic distance to the Bohr radius, electronic correlations beyond RPA have a non-negligible effect on the structural properties. Additionally, the applicability of the hypernetted chain approximation for the calculation of the structural properties using the screened pair interaction potential is analyzed employing the effective coupling parameter approach.
physics.plasm-ph↗
Wakefields in streaming plasmas: Characteristics of the induced charge density distribution
Motivated by experiments on the generation of streaming plasmas in high energy density facilities, industrial setups, and fundamental dusty plasma research the plasma polarization around a test charge in streaming plasmas is considered. The induced charge density distribution of plasma constituents is discussed for the subsonic, sonic, and supersonic regime. Also, it is shown that the plasma polarization in the vicinity of the test charge shows different scaling in subsonic and supersonic regimes.
physics.plasm-ph↗
Ion Potential in Non-ideal Dense Quantum Plasmas
The screened ion potential in non-ideal dense quantum plasmas is investigated by invoking the Singwi-Tosi-Land-Sjölander approximation for the electronic local field correction at densities $r_s\lesssim 2$ and degeneracy parameters $θ\lesssim 1$, where $r_s$ is the ratio of the mean inter-particle distance to the first Bohr radius, and $θ$ is the ratio of the thermal energy to the Fermi energy of the electrons. Various cross-checks with ion potentials obtained from ground state quantum Monte-Carlo data, the random phase approximation, as well as with existing analytical models are presented. Further, the importance of the electronic correlation effects for the dynamics in strongly coupled ionic subsystems for $0.1\leq r_s\leq 2$ is discussed.
physics.plasm-ph↗
Gradient correction and Bohm potential for 2D and 1D electron gases at a finite temperature
From the static polarization function of electrons in the random phase approximation the quantum Bohm potential for the quantum hydrodynamic description of electrons, and the density gradient correction to the Thomas-Fermi free energy at a finite temperature for the 2D and 1D cases are derived. The behavior of the Bohm potential and of the density gradient correction as a function of the degeneracy parameter is discussed. Based on recent developments in the fluid description of quantum plasmas, the Bohm potential for the high frequency domain is presented.
physics.plasm-ph↗
Theoretical foundations of quantum hydrodynamics for plasmas
Beginning from the semiclassical Hamiltonian, the Fermi pressure and Bohm potential for the quantum hydrodynamics application (QHD) at finite temperature are consistently derived in the framework of the local density approximation with the first order density gradient correction. Previously known results are revised and improved with a clear description of the underlying approximations. A fully non-local Bohm potential, which goes beyond of all previous results and is linked to the electron polarization function in the random phase approximation, for the QHD model is presented. The dynamic QHD exchange correlation potential is introduced in the framework of local field corrections, and considered for the case of the relaxation time approximation. Finally, the range of applicability of the QHD is discussed.
physics.plasm-ph↗