arXiv subjects

D. Kremp

Publications and source records attributed to D. Kremp.

13 recordsLinked to original sources

arXiv2004

Monte Carlo results for the hydrogen Hugoniot

We propose a theoretical Hugoniot obtained by combining results for the equation of state (EOS) from the Direct Path Integral Monte Carlo technique (DPIMC) and those from Reaction Ensemble Monte Carlo (REMC) simulations. The main idea of such proposal is based on the fact that DPMIC provides first-principle results for a wide range of densities and temperatures including the region of partially ionized plasmas. On the other hand, for lower temperatures where the formation of molecules becomes dominant, DPIMC simulations become cumbersome and inefficient. For this region it is possible to use accurate REMC simulations where bound states (molecules) are treated on the Born-Oppenheimer level using a binding potential calculated by Kolos and Wolniewicz. The remaining interaction is then reduced to the scattering between neutral particles which is reliably treated classically applying effective potentials. The resulting Hugoniot is located between the experimental values of Knudson {\textit{et al.}} \cite{1} and Collins {\textit{et al.}} \cite{2}.

physics.plasm-ph↗

arXiv2001

Plasmon dispersion of a weakly degenerate nonideal one-component plasma

Classical Molecular Dynamics simulations (MD) for a one-component weakly degenerate plasma are presented. Using an effective quantum pair potential (Kelbg potential), the dynamic structure factor and the dispersion of Langmuir waves are computed. The influence of the coupling strength $Γ$ and degree of degeneracy $ρΛ^3$ on these properties is discussed. The results are compared with predictions of mean-field theories.

cond-mat.str-el↗

arXiv2001

Dielectric properties of correlated quantum plasmas

Results for the dynamic structure factor of a one-component plasma are presented for the situations of strong coupling and weak degeneracy and strong degeneracy and weak coupling. Possibilities to obtain rigorous results when both, coupling and degeneracy are large are discussed.

cond-mat.stat-mech↗

arXiv2001

Path integral Monte Carlo simulations and analytical approximations for high-temperature plasmas

The results of analytical approximations and extensive calculations based on a path integral Monte Carlo (PIMC) scheme are presented. A new (direct) PIMC method allows for a correct determination of thermodynamic properties such as energy and equation of state of dense degenerate Coulomb systems. In this paper, we present results for dense partially ionized hydrogen at intermediate and high temperature. We give a quantitative comparison with the available results of alternative (restricted) PIMC simulations and with analytical expressions based on iterpolation formulas meeting the exact limits at low and high densities. Good agreement between the two simulations is found up to densities of the order of $10^{24}cm^{-3}$. The agreement with the analytical results is satisfactory up to densities in the range $10^{22}... 10^{23}cm^{-3}$.

astro-ph↗

arXiv2001

Kadanoff-Baym equations and non-Markovian Boltzmann equation in generalized T-matrix approximation

A recently developed method for incorporating initial binary correlations into the Kadanoff-Baym equations (KBE) is used to derive a generalized T-matrix approximation for the self-energies. It is shown that the T-matrix obtains additional contributions arising from initial correlations. Using these results and taking the time-diagonal limit of the KBE, a generalized quantum kinetic equation in binary collision approximation is derived. This equation is a far-reaching generalization of Boltzmann-type kinetic equations: it selfconsistently includes memory effects (retardation, off-shell T-matrices) as well as many-particle effects (damping, in-medium T-Matrices) and spin-statistics effects (Pauli-blocking).

cond-mat.stat-mech↗

arXiv2000

Dynamical Properties and Plasmon Dispersion of a Weakly Degenerate Correlated One-Component Plasma

Classical Molecular Dynamics (MD) simulations for a one-component plasma (OCP) are presented. Quantum effects are included in the form of the Kelbg potential. Results for the dynamical structure factor are compared with the Vlasov and RPA (random phase approximation) theories. The influence of the coupling parameter $Γ$, degeneracy parameter $ρΛ^3$ and the form of the pair interaction on the optical plasmon dispersion is investigated. An improved analytical approximation for the dispersion of Langmuir waves is presented.

physics.plasm-ph↗

arXiv2000

Harmonics generation in electron-ion collisions in a short laser pulse

Anomalously high generation efficiency of coherent higher field-harmonics in collisions between {\em oppositely charged particles} in the field of femtosecond lasers is predicted. This is based on rigorous numerical solutions of a quantum kinetic equation for dense laser plasmas which overcomes limitations of previous investigations.

cond-mat↗

arXiv1999

Quantum kinetic theory for dense Coulomb systems in strong electromagnetic fields

A quantum kinetic theory for correlated charged-particle systems in strong time-dependent electromagnetic fields is developed. Our approach is based on a systematic gauge-invariant nonequilibrium Green's functions formulation. We concentrate on the selfconsistent treatment of dynamical screening and electromagnetic fields which is applicable to arbitrary nonequilibrium situations. Numerical results for the nonlinear plasma heating by the laser field and the electron-ion collision frequency including multi-photon absorption (inverse bremsstrahlung) are presented.

cond-mat.str-el↗

arXiv1999

Quantum Kinetic Theory for Laser Plasmas. Dynamical Screening in Strong Fields

A quantum kinetic theory for correlated charged-particle systems in strong time-dependent electromagnetic fields is developed. Our approach is based on a systematic gauge-invariant nonequilibrium Green's functions formulation. Extending our previous analysis (Kremp et al., Phys. Rev. E vol. 60, p. 4725 (1999) we concentrate on the selfconsistent treatment of dynamical screening and electromagnetic fields which is applicable to arbitrary nonequilibrium situations. The resulting kinetic equation generalizes previous results to quantum plasmas with full dynamical screening and includes many-body effects. It is, in particular, applicable to the interaction of dense plasmas with strong electromagnetic fields, including laser fields and x-rays. Furthermore, results for the modification of the plasma screening and the longitudinal field fluctuations due to the electromagnetic field are presented.

cond-mat.stat-mech↗

arXiv1999

Kadanoff-Baym Equations with Initial Correlations

The Kadanoff-Baym equations (KBE) are usually derived under the assumption of the weakening of initial correlations (Bogolyubov's condition) and, therefore, fail to correctly describe the short time behavior. We demonstrate that this assumption is not necessary. Using functional derivatives techniques, we present a straightforward generalization of the KBE which allows to include arbitrary initial correlations and which is more general than previous derivations. As a result, an additional collision integral is obtained which is being damped out after a few collisions. Our results are complemented with numerical investigations showing the effect of initial correlations.

cond-mat.stat-mech↗

arXiv1999

Short time dynamics with initial correlations

The short-time dynamics of correlated systems is strongly influenced by initial correlations giving rise to an additional collision integral in the non-Markovian kinetic equation. Exact cancellation of the two integrals is found if the initial state is thermal equilibrium which is an important consistency criterion. Analytical results are given for the time evolution of the correlation energy which are confirmed by comparisons with molecular dynamics simulations (MD).

physics.plasm-ph↗

arXiv1999

The two-particle problem in a many-particle system: I. Dynamically screened ladder approximation

The two-particle problem within a nonequilibrium many-particle system is investigated in the framework of real-time Green's functions. Starting from the dynamically screened ladder approximation of the nonequlibrium Bethe-Salpeter equation, a nonequilibrium Dyson equation is given for two-time two-particle Green's functions. Thereby the well-known Kadanoff-Baym equations are generalized to the case of two-particle functions. The two-time structure of the equations is achieved in an exact way avoiding the so-called Shindo approximation. For the case of thermodynamic equilibrium, the differences to former results obtained for the effective two-particle hamiltonian are discussed.

physics.plasm-ph↗

arXiv1993

In-medium relativistic kinetic theory and nucleon-meson systems

Within the $σ-ω$ model of coupled nucleon-meson systems, a generalized relativistic Lenard--Balescu--equation is presented resulting from a relativistic random phase approximation (RRPA). This provides a systematic derivation of relativistic transport equations in the frame of nonequilibrium Green's function technique including medium effects as well as fluctuation effects. It contains all possible processes due to one meson exchange and special attention is kept to the off--shell character of the particles. As a new feature of many particle effects, processes are possible which can be interpreted as particle creation and annihilation due to in-medium one meson exchange. In-medium cross sections are obtained from the generalized derivation of collision integrals, which possess complete crossing symmetries.

nucl-th↗