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Nicolas Desbiens

Bio: Nicolas Desbiens is an academic researcher. The author has contributed to research in topics: Nuclear reaction & Warm dense matter. The author has an hindex of 7, co-authored 9 publications receiving 148 citations.

Papers
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Journal ArticleDOI
TL;DR: A detailed review of the state-of-the-art EOS models for inertial confinement fusion (ICF) implosions can be found in this paper, where the authors present a detailed comparison with experiments.

65 citations

Journal ArticleDOI
TL;DR: The concept of an effective one component plasma is used to quantify the overcorrelation of the light element induced by the admixture of a heavy element and comparison to a global pseudo ion in jellium model is presented.
Abstract: Transport properties of mixtures of elements in the dense plasma regime play an important role in natural astrophysical and experimental systems, eg, inertial confinement fusion We present a series of orbital-free molecular dynamics simulations on dense plasma mixtures with comparison to a global pseudo ion in jellium model Hydrogen is mixed with elements of increasingly high atomic number (lithium, carbon, aluminum, copper, and silver) at a fixed temperature of 100 eV and constant pressure set by pure hydrogen at 2g/cm^{3}, namely, 370 Mbars We compute ionic transport coefficients, such as self-diffusion, mutual diffusion, and viscosity for various concentrations Small concentrations of the heavy atoms significantly change the density of the plasma and decrease the transport coefficients The structure of the mixture evidences a strong Coulomb coupling between heavy ions and the appearance of a broad correlation peak at short distances between hydrogen atoms The concept of an effective one component plasma is used to quantify the overcorrelation of the light element induced by the admixture of a heavy element

29 citations

Journal ArticleDOI
TL;DR: In this paper, a parametrization of the pair correlation function and the static structure factor of the Coulomb one component plasma (OCP) from the weakly coupled regime to the strongly coupled regime is presented.
Abstract: We present a parametrization of the pair correlation function and the static structure factor of the Coulomb one component plasma (OCP) from the weakly coupled regime to the strongly coupled regime. Recent experiments strongly suggest that the OCP model can play the role of a reference system for warm dense matter. It can provide the ionic static structure factor that is necessary to interpret the x-ray Thomson scattering measurements, for instance. We illustrate this with the interpretation of a x-ray diffraction spectrum recently measured, using a Bayesian method that requires many evaluations of the static structure factor to automatically calibrate the parameters. For strongly coupled dusty plasmas, the proposed parametrization of the Coulomb OCP pair correlation function can be related to the Yukawa one, including screening. Further prospects to parametrize the static structure of Yukawa systems are also discussed.

26 citations

Journal ArticleDOI
TL;DR: In this paper, a parametrization of the pair correlation function and the static structure factor of the Coulomb one component plasma (OCP) from the weakly coupled regime to the strongly coupled regime is presented.
Abstract: We present a parametrization of the pair correlation function and the static structure factor of the Coulomb one component plasma (OCP) from the weakly coupled regime to the strongly coupled regime. Recent experiments strongly suggest that the OCP model can play the role of a reference system for warm dense matter. It can provide the ionic static structure factor that is necessary to interpret the x-ray Thomson scattering measurements, for instance. We illustrate this with the interpretation of an x-ray diffraction spectrum recently measured, using a Bayesian method that requires many evaluations of the static structure factor to automatically calibrate the parameters. For strongly coupled dusty plasmas, the proposed parametrization of the Coulomb OCP pair correlation function can be related to the Yukawa one, including screening. Further prospects to parametrize the static structure of Yukawa systems are also discussed.

25 citations

Journal ArticleDOI
TL;DR: A simple, fast, and promising method to compute the melting curves of materials with ab initio molecular dynamics, based on the two-phase thermodynamic model of Lin et al, comparable to the most sophisticated methods, for a much lower computational cost.
Abstract: We present a simple, fast, and promising method to compute the melting curves of materials with ab initio molecular dynamics. It is based on the two-phase thermodynamic model of Lin et al [J. Chem. Phys. 119, 11792 (2003)] and its improved version given by Desjarlais [Phys. Rev. E 88, 062145 (2013)]. In this model, the velocity autocorrelation function is utilized to calculate the contribution of the nuclei motion to the entropy of the solid and liquid phases. It is then possible to find the thermodynamic conditions of equal Gibbs free energy between these phases, defining the melting curve. The first benchmark on the face-centered cubic melting curve of aluminum from 0 to 300 GPa demonstrates how to obtain an accuracy of 5%--10%, comparable to the most sophisticated methods, for a much lower computational cost.

16 citations


Cited by
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Journal ArticleDOI
TL;DR: In this article, Zhou et al. presented the initial condition dependence of Rayleigh-Taylor (RT) and Richtmyer-Meshkov (RM) mixing layers, and introduced parameters that are used to evaluate the level of mixedness and mixed mass within the layers.

606 citations

Journal ArticleDOI
TL;DR: The first controlled fusion experiment on the National Ignition Facility to produce capsule gain greater than unity (here 5.8) and reach ignition by many different formulations of the Lawson criterion was reported in this paper .
Abstract: For more than half a century, researchers around the world have been engaged in attempts to achieve fusion ignition as a proof of principle of various fusion concepts. As recently reported, a burning plasma state, where the alpha-heating in the plasma is the primary source of heating, was achieved in laboratory experiments. Following the Lawson criterion, an ignited plasma is one where the fusion heating power is high enough to overcome all the physical processes that cool the fusion plasma, creating a positive thermodynamic feedback loop with rapidly increasing temperature. In inertially confined fusion, ignition is a state where the fusion plasma can begin ``burn propagation'' into surrounding cold fuel, enabling the possibility of high energy gain. While ``scientific breakeven'' (i.e. unity target gain) has not yet been achieved, this talk reports the first controlled fusion experiment on the National Ignition Facility to produce capsule gain greater than unity (here 5.8) and reach ignition by many different formulations of the Lawson criterion. In the talk, we will discuss some key basic physics inertial confinement fusion (ICF) principles behind the burning plasma and ignition results as well as discuss future challenges.

100 citations

Journal ArticleDOI
05 Aug 2020-Nature
TL;DR: Researchers have measured the equation of state of hydrocarbon in a high-density regime, which is necessary for accurate modelling of the oscillations of white dwarf stars and predicts an increase in compressibility due to ionization of the inner-core orbitals of carbon.
Abstract: White dwarfs represent the final state of evolution for most stars1–3. Certain classes of white dwarfs pulsate4,5, leading to observable brightness variations, and analysis of these variations with theoretical stellar models probes their internal structure. Modelling of these pulsating stars provides stringent tests of white dwarf models and a detailed picture of the outcome of the late stages of stellar evolution6. However, the high-energy-density states that exist in white dwarfs are extremely difficult to reach and to measure in the laboratory, so theoretical predictions are largely untested at these conditions. Here we report measurements of the relationship between pressure and density along the principal shock Hugoniot (equations describing the state of the sample material before and after the passage of the shock derived from conservation laws) of hydrocarbon to within five per cent. The observed maximum compressibility is consistent with theoretical models that include detailed electronic structure. This is relevant for the equation of state of matter at pressures ranging from 100 million to 450 million atmospheres, where the understanding of white dwarf physics is sensitive to the equation of state and where models differ considerably. The measurements test these equation-of-state relations that are used in the modelling of white dwarfs and inertial confinement fusion experiments7,8, and we predict an increase in compressibility due to ionization of the inner-core orbitals of carbon. We also find that a detailed treatment of the electronic structure and the electron degeneracy pressure is required to capture the measured shape of the pressure–density evolution for hydrocarbon before peak compression. Our results illuminate the equation of state of the white dwarf envelope (the region surrounding the stellar core that contains partially ionized and partially degenerate non-ideal plasmas), which is a weak link in the constitutive physics informing the structure and evolution of white dwarf stars9. Researchers have measured the equation of state of hydrocarbon in a high-density regime, which is necessary for accurate modelling of the oscillations of white dwarf stars.

64 citations

Journal Article
TL;DR: In this paper, an X-ray diffraction from polystyrene (C8H8n) samples was used to demonstrate the necessity of high pressures for carbon-hydrogen separation.
Abstract: The effects of hydrocarbon reactions and diamond precipitation on the internal structure and evolution of icy giant planets such as Neptune and Uranus have been discussed for more than three decades1. Inside these celestial bodies, simple hydrocarbons such as methane, which are highly abundant in the atmospheres2, are believed to undergo structural transitions3,4 that release hydrogen from deeper layers and may lead to compact stratified cores5–7. Indeed, from the surface towards the core, the isentropes of Uranus and Neptune intersect a temperature–pressure regime in which methane first transforms into a mixture of hydrocarbon polymers8, whereas, in deeper layers, a phase separation into diamond and hydrogen may be possible. Here we show experimental evidence for this phase separation process obtained by in situ X-ray diffraction from polystyrene (C8H8)n samples dynamically compressed to conditions around 150 GPa and 5,000 K; these conditions resemble the environment around 10,000 km below the surfaces of Neptune and Uranus9. Our findings demonstrate the necessity of high pressures for initiating carbon–hydrogen separation3 and imply that diamond precipitation may require pressures about ten times as high as previously indicated by static compression experiments4,8,10. Our results will inform mass–radius relationships of carbon-bearing exoplanets11, provide constraints for their internal layer structure and improve evolutionary models of Uranus and Neptune, in which carbon–hydrogen separation could influence the convective heat transport7.Diamonds precipitate from methane under the intense pressures of the atmospheres of Neptune and Uranus. Here, a laser shock experiment on a hydrocarbon sample shows that diamonds may require ten times as much pressure to precipitate as was previously thought.

56 citations