The aim of this paper is to provide experimental data on various expanded elements in the warm dense matter regime. The experiments were done on the experimental facility “enceinte à plasma isochore” and are evaluated through a thorough comparison with ab initio calculations, average-atom codes, and chemical models. This comparison allows for the evaluation of the experimental temperatures that are not accessible to the measurements and permits the building of useful data tables gathering energy, pressure, conductivity, and temperatures. We summarize experiments performed on aluminum (0.1 and 0.3 g/cm3), nickel (0.2 g/cm3), titanium (0.1 g/cm3), copper (0.3 and 0.5 g/cm3), silver (0.43 g/cm3), gold (0.5 g/cm3), boron (0.094 g/cm3), and silicon (0.21 g/cm3) for temperatures ranging from 0.5 eV to 3-4 eV.

Exploring and understanding ultrafast processes at the atomic level is a scientific challenge. Femtosecond X-ray absorption spectroscopy (XAS) arises as an essential experimental probing method, as it can simultaneously reveal both electronic and atomic structures, and thus potentially unravel their nonequilibrium dynamic interplay which is at the origin of most of the ultrafast mechanisms. However, despite considerable efforts, there is still no femtosecond X-ray source suitable for routine experiments. Here we show that betatron radiation from relativistic laser−plasma interaction combines ideal features for femtosecond XAS. It has been used to investigate the nonequilibrium dynamics of a copper sample brought at extreme conditions of temperature and pressure by a femtosecond laser pulse. We measured a rise-time of the electron temperature below 100 fs. This experiment demonstrates the great potential of the table-top betatron source which makes possible the investigation of unexplored ultrafast processes in manifold fields of research.

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This paper presents an improved analytical expression for the x-ray dynamic structure factor from a dense plasma which includes the effects of weakly bound electrons. This result can be applied to describe scattering from low to moderate Z plasmas, and it covers the entire range of plasma conditions that can be found in inertial confinement fusion experiments, from ideal to degenerate up to moderately coupled systems. The theory is used to interpret x-ray scattering experiments from solid density carbon plasmas and to extract accurate measurements of electron temperature, electron density, and charge state. The experimental results are applied to validate various equation-of-state models for carbon plasmas.

Isochore measurements were performed in the warm dense matter regime. Pressure and internal energy variation of aluminum plasma (density 0.1 g/cm(3) and 0.3 g/cm(3)) are measured using a homogeneous and thermally equilibrated media produced inside an isochoric plasma closed vessel in the internal energy range 20-50 MJ/kg. These data are compared to detailed calculations obtained from ab initio quantum molecular dynamics, average atom model within the framework of the density functional theory, and standard theories. A dispersion between theoretical isochore equation of state is found in the studied experimental thermodynamic regime.

Calculations of equation of state, transport coefficients, and stopping power of dense plasmas are presented. Theoretical results have been obtained using the first-principles average-atom model self-consistent approach for astrophysical and laboratory plasmas (SCAALP) based on the finite-temperature density-functional theory and the Gibbs–Bogolyubov inequality. Numerical results, comparisons with molecular dynamics, and Monte Carlo simulations and experiments are presented and discussed in the high energy density physics domain including part of the warm dense matter regime. Results show that the average-atom model SCAALP is well suited to describe thermodynamic and transport properties for a wide range of high energy density physics applications.

We have used point-projection K-shell absorption spectroscopy to infer the ionization and recombination dynamics of transient aluminum plasmas. Two femtosecond beams of the 100 TW laser at the LULI facility were used to produce an aluminum plasma on a thin aluminum foil (83 or 50 nm), and a picosecond x-ray backlighter source. The short-pulse backlighter probed the aluminum plasma at different times by adjusting the delay between the two femtosecond driving beams. Absorption x-ray spectra at early times are characteristic of a dense and rather homogeneous plasma. Collisional-radiative atomic physics coupled with hydrodynamic simulations reproduce fairly well the measured average ionization as a function of time.

Using ultrafast x-ray probing, we experimentally observed a progressive loss of ordering within solid-density aluminum as the temperature raises from 300 K to >10{4} K. The Al sample was isochorically heated by a short ( approximately ps), laser-accelerated proton beam and probed by a short broadband x-ray source around the Al K edge. The loss of short-range ordering is detected through the progressive smoothing of the time-resolved x-ray absorption near-edge spectroscopy (XANES) structure. The results are compared with two different theoretical models of warm dense matter and allow us to put an upper bound on the onset of ion lattice disorder within the heated solid-density medium of approximately 10 ps.