Mass-radius relationships for exoplanets

For planets other than Earth, interpretation of the composition and structure depends largely on comparing the mass and radius with the composition expected given their distance from the parent star. The composition implies a mass-radius relation which relies heavily on equations of state calculated from electronic structure theory and measured experimentally on Earth. We lay out a method for deriving and testing equations of state, and deduce mass-radius and mass-pressure relations for key materials whose equation of state is reasonably well established, and for differentiated Fe/rock. We find that variations in the equation of state, such as may arise when extrapolating from low pressure data, can have significant effects on predicted mass- radius relations, and on planetary pressure profiles. The relations are compared with the observed masses and radii of planets and exoplanets. Kepler-10b is apparently 'Earth- like,' likely with a proportionately larger core than Earth's, nominally 2/3 of the mass of the planet. CoRoT-7b is consistent with a rocky mantle over an Fe-based core which is likely to be proportionately smaller than Earth's. GJ 1214b lies between the mass-radius curves for H2O and CH4, suggesting an 'icy' composition with a relatively large core or a relatively large proportion of H2O. CoRoT-2b is less dense than the hydrogen relation, which could be explained by an anomalously high degree of heating or by higher than assumed atmospheric opacity. HAT-P-2b is slightly denser than the mass-radius relation for hydrogen, suggesting the presence of a significant amount of matter of higher atomic number. CoRoT-3b lies close to the hydrogen relation. The pressure at the center of Kepler-10b is 1.5+1.2-1.0 TPa. The central pressure in CoRoT-7b is probably close to 0.8TPa, though may be up to 2TPa.Comment: Added more recent exoplanets. Tidied text and references. Added extra "rock" compositions. Responded to referee comment

Viscosity coefficient of dense fluid hydrogen

Evaluations of the viscosity of the dense hydrogen are presented in a region whese dissociation plays a major role. The viscosity is computed by a classical molecular dynamics model where the fraction of dissociated hydrogen is a priori given by the Ross model. A universal fit is given, based on scaling laws of inverse power potential

Contributions to Plasma PhysicsVolume 59, Issues 4-5 & 6: Special Issues: Part I & II

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The role of nuclear reactions and alpha-particle transport in the dynamics of Inertial Confinement Fusion capsules

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Approche sans orbitale des plasmas denses

Les propriétés microscopiques des plasmas chauds et denses plasmas couplés constituent un domaine d étude essentiellement exploré par les théories de physique classique telles que le plasma à une composante, théorie basée sur un certain nombre de paramètres ajustables, en particulier l ionisation. Nous nous proposons, dans ce travail de thèse, d aborder cette thématique par une approche sans paramètre fondée sur le couplage cohérent de la dynamique moléculaire classique des noyaux et de la théorie de la fonctionnelle de la densité sans orbitale pour les électrons. La composante électronique est ainsi représentée par une énergie libre semi-classique dont la seule variable pertinente est la densité locale. Le modèle a été validé par comparaison avec une méthode ab initio, la dynamique moléculaire quantique, qui décrit également le fluide électronique par une énergie libre mais exprimée au moyen d une théorie quantique de particules indépendantes. Suite à cette validation, la dynamique moléculaire sans orbitale a été mise à profit pour évaluer l équation d état, à l équilibre thermodynamique, de plasmas de bore et de fer à très haute température et densité. Des comparaisons avec les modèles classiques ont été entreprises sur les propriétés structurales et dynamiques. Enfin, les lois de mélange d équations d état ou de coefficient de transport ont été vérifiées par simulation directe d un plasma constitué de deutérium et de cuivre.The microscopic properties of hot and dense plasmas stay a field essentially studied thanks to classical theories like the One Component Plasma, models which rely on free parameters, particularly ionisation. In order to investigate these systems, we have used, in this PhD work, a semiclassical model, without free parameters, that is based on coupling consistently classical molecular dynamics for nuclei and orbital free density functional theory for the electrons. The electronic fluid is represented by a free energy entirely determined by the local density. This approximation was validated by a comparison with an ab initio technique, quantum molecular dynamics. This one is identical to the previous except for the description of free energy that depends on a quantum-independent-particle model. Orbital free molecular dynamics was then used to compute equation of state of boron and iron plasmas in the hot and dense regime. Furthermore, comparisons with classical theories were performed on structural and dynamical properties. Finally, equation of state and transport coefficients mixing laws were studied by direct simulation of a plasma composed of deuterium and copper.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Theoretical and experimental refraction index of shock compressed and pre-compressed water in the megabar pressure range

The refraction index of water at megabar pressures was calculated ab initio with the quantum molecular dynamics (QMD) package ABINIT using the projector augmented (PAW) formalism. Calculations were compared to experimental results obtained by laser-driven shocks on water in standard conditions and on water samples statically precompressed at ${\approx}10\ \text{kBar}$ . The refraction index was measured in transparent and opaque states of water using a VISAR diagnostics. We also modelled the data using an extended Lorentz-Drude model. At high compressions, a strong increase of the refraction index is observed both in experimental results and in the theoretical calculations, which is an indication of water approaching band gap closure

Sudden diffusion of turbulent mixing layers in weakly coupled plasmas under compression

International audienceThe rapid growth of viscosity driven by temperature increase in turbulent plasmas under compression induces a sudden dissipation of kinetic energy, eventually leading to the relaminarization of the flow [Davidovits and Fisch, Phys. Rev. Lett. 116, 105004 (2016)]. The interdiffusion between species is also greatly enhanced, so that mixing layers appearing at interfaces between different materials are subjected to strong dynamical modifications. The result is a competition between the vanishing turbulent diffusion and the expanding plasma microscopic diffusion. In direct numerical simulations with conditions relevant to inertial confinement fusion, we evidence regimes where compressed spherical mixing layers are quickly diffused during the relaminarization process. Using one and two-point turbulent statistics, we also detail how mixing heterogeneities are smoothed out