Thermodynamic and transport properties of Fe-Ni alloys in the Warm Dense Matter regime
Warm Dense Matter (WDM) lies at the intersection of condensed matter physics and
plasma physics. In particular, it is characterized by temperatures comparable to those of the
Fermi level (1,000 to 10,000 K) and densities on the order of those of solids. In this
state of matter, a thorough understanding of the phase diagram and transport properties, such as
electrical conductivity, is crucial for modeling the magnetospheres of rocky planets,
hydrodynamic instabilities encountered in inertial confinement fusion experiments,
or during giant impacts, such as the one believed to have formed the Moon from the collision between
Earth and Theia.
For several years now, the Laboratory for Matter under Extreme Conditions at CEA DAM Île-de-France developed
an experimental facility (Pulsed Plasma Chamber—EPP) dedicated to the study of WDM. Using
pulsed-power discharges with very high currents (20–500 kA), this experimental facility enables the investigation of
changes in the thermodynamic and transport properties of matter as it transitions from the solid state to
the plasma state over time scales of the order of hundreds of nanoseconds. Very recently, these experiments
have been carried out using an X-ray synchrotron source to evaluate the electronic state density of the plasmas encountered in the EPP experiments.
This PhD will focus on the study of thermodynamic and transport properties of a
binary iron-nickel alloy within a pressure-temperature range associated with giant impacts. To this end, experiments will be conducted both at the CEA DAM Île-de-France site and at a synchrotron facility in order to investigate the thermodynamic, optical, and transport properties of Fe-Ni. The experimental data collected will then be compared with quantum molecular dynamics simulations that provide information, in particular, on the electronic states observed during the experiments. Finally, new theoretical approaches, based on the experimental and numerical results, will need to be proposed in order to improve the modeling of this type of alloy in the WDM regime.
Attosecond photoemission spectroscopy of molecular gases and liquids
The aim of the thesis is to perform attosecond photoemission spectroscopy on molecules in the gas and liquid phase exploiting a novel high repetition rate Ytterbium laser system. These studies will unveil the processes of photoionization of inner/outer shells and the dynamics of electron scattering in real time.
microstructure informed kinetic model : application to solid explosives
When an explosive composition is subjected to an intense stress, such as a shock, the wave generated interacts with the microstructure and in particular with the defects it contains. Due to the nature of the defects, the energy can be localised, as when porosity is compacted, which can lead to the appearance of hot spots. Beyond a certain critical size, these hot spots grow as a result of the chemical decomposition of the explosive, and in some cases this can lead to the creation of a detonation wave. The role of these hot spots is therefore decisive in the initiation of solid explosives. The majority of macroscopic models used to study the shock-detonation transition (SDT) are phenomenological models calibrated on experiments (e.g. multi-strand gauge experiments) and therefore do not take into account the microstructural peculiarities specific to each explosive. It then becomes necessary to recalibrate a model for each composition, which limits any predictive capacity.
Microtomographic studies of real microstructures of explosive compositions have revealed that these deviate significantly from an average description based on a spherical pore. Through image segmentation, these microtomographs can provide essential ingredients for mesoscopic-scale simulation codes: these microstructures can be used directly as input for calculations or as a basis for generating virtual but realistic microstructures, thereby extending the accessible database given the experimental difficulties in generating this type of image in large numbers.
The computing power available today means that we can now envisage explicit simulations of realistic microstructures of explosive compositions. These simulations, in two or even three dimensions, will form the basis for the construction of a macroscopic kinetics model for modelling the shock-detonation transition. The results expected from this work are cross-disciplinary and can be transposed to all composite energetic materials. The effect of thermal or mechanical damage on the behaviour of an explosive or a solid propellant (vulnerability issues) could also benefit from this project. This more detailed knowledge of the role of microstructure (grain shape, porosity, etc.) could also improve filler manufacturing processes (e.g. ‘Very Insensitive’-RDX).