Path Integral Monte Carlo and Density Functional Molecular Dynamics Simulations of Hot, Dense Helium

Two first-principles simulation techniques, path integral Monte Carlo (PIMC) and density functional molecular dynamics (DFT-MD), are applied to study hot, dense helium in the density-temperature range of 0.387 - 5.35 g/cc and 500 K - 1.28x10^8 K. One coherent equation of state (EOS) is derived by combining DFT-MD data at lower temperatures with PIMC results at higher temperatures. Good agreement between both techniques is found in an intermediate temperature range. For the highest temperatures, the PIMC results converge to the Debye-Hueckel limiting law. In order derive the entropy, a thermodynamically consistent free energy fit is introduced that reproduces the internal energies and pressure derived from the first-principles simulations. The equation of state is presented in form of a table as well as a fit and is compared with chemical models. In addition, the structure of the fluid is analyzed using pair correlation functions. Shock Hugoniot curves are compared with recent laser shock wave experiments.Comment: 16 pages, 15 figure

Dense plasmas in astrophysics: from giant planets to neutron stars

We briefly examine the properties of dense plasmas characteristic of the interior of giant planets and the atmospheres of neutron stars. Special attention is devoted to the equation of state of hydrogen and helium at high density and to the effect of magnetic fields on the properties of dense matter.Comment: Invited Review, Strongly Coupled Coulomb Systems, Moscow June 2005; to appear in Journal of Physics

Phase Transition in Strongly Degenerate Hydrogen Plasma

Direct fermionic path-integral Monte-Carlo simulations of strongly coupled hydrogen are presented. Our results show evidence for the hypothetical plasma phase transition. Its most remarkable manifestation is the appearance of metallic droplets which are predicted to be crucial for the electrical conductivity allowing to explain the rapid increase observed in recent shock compression measurments.Comment: 1 LaTeX file using jetpl.cls (included), 5 ps figures. Manuscript submitted to JETP Letter

DOI:10.1068/htwu586 Determination of liquid ^ vapour phase boundaries by a dynamic experimental method

Abstract. Shock compression and the following expansion into helium were used to generate the boiling of porous nickel. The brightness temperature and velocity of expansion were measured by a fast multichannel optical pyrometer. Gas dynamic peculiarities of expansion in the final pressure range below 0.4 GPa were studied. It has been proved that a shock rarefaction wave is formed under expansion when final states of the sample are inside the two-phase region. The fast heating of tungsten by multiple shocked helium in the process of acceleration of tungsten foil at dynamically formed isobaric conditions is proposed as a new way for generating nearcritical-point states of liquid ^ vapour phase transition. Additionally, an estimation of the critical point data of tungsten is made.

Phase transition in a strongly nonideal deuterium plasma generated by quasi-isentropical compression at megabar pressures

High-explosive driven generators of cylindrical and plane shock waves in D-2 and H-2 were used for the generation of warm and dense strongly nonideal matter with an intense interparticle interaction and Fermi statistics. Highly resolved flash x-ray diagnostics were used to measure the adiabatic plasma compressibility. The thermodynamic measurements demonstrated the 20% increase of density at megabar pressure, just in the density range, where the electrical measurements indicated a sharp - 5 orders of magnitude - increase of electrical conductivity due to pressure ionization in strongly coupled plasmas