Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userAnalysis of laser shock experiments on precompressed samples using a quartz reference and application to warm dense hydrogen and helium
96
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Megabar (1 Mbar = 100 GPa) laser shocks on precompressed samples allow reaching unprecedented high densities and moderately high 10000-100000K temperatures. We describe here a complete analysis framework for the velocimetry (VISAR) and pyrometry (SOP) data produced in these experiments. Since the precompression increases the initial density of both the sample of interest and the quartz reference for pressure-density, reflectivity and temperature measurements, we describe analytical corrections based on available experimental data on warm dense silica and density-functional-theory based molecular dynamics computer simulations. Using our improved analysis framework we report a re-analysis of previously published data on warm dense hydrogen and helium, compare the newly inferred pressure, density and temperature data with most advanced equation of state models and provide updated reflectivity values.
rate research
Read More
We study the thermophysical properties of warm dense hydrogen using quantum molecular dynamics simulations. New results are presented for the pair distribution functions, the equation of state, the Hugoniot curve, and the reflectivity. We compare with available experimental data and predictions of the chemical picture. Especially, we discuss the nonmetal-to-metal transition which occurs at about 40 GPa in the dense fluid.
We present new experiments to study the formation of radiative shocks and the interaction between two counter-propagating radiative shocks. The experiments were performed at the Orion laser facility which was used to drive shocks in xenon inside large aspect ratio gas-cells. The collision between the two shocks and their respective radiative precursors, combined with the formation of inherently 3-dimensional shocks, provides a novel platform particularly suited for benchmarking of numerical codes. The dynamics of the shocks before and after the collision were investigated using point-projection X-ray backlighting while, simultaneously, the electron density in the radiative precursor was measured via optical laser interferometry. Modelling of the experiments using the 2-D radiation hydrodynamic codes NYM/PETRA show a very good agreement with the experimental results.
We report on the design and first results from experiments looking at the formation of radiative shocks on the Shenguang-II (SG-II) laser at the Shanghai Institute of Optics and Fine Mechanics in China. Laser-heating of a two-layer CH/CH-Br foil drives a $sim$40 km/s shock inside a gas-cell filled with argon at an initial pressure of 1 bar. The use of gas-cell targets with large (several mm) lateral and axial extent allows the shock to propagate freely without any wall interactions, and permits a large field of view to image single and colliding counter-propagating shocks with time resolved, point-projection X-ray backlighting ($sim20$ $mu$m source size, 4.3 keV photon energy). Single shocks were imaged up to 100 ns after the onset of the laser drive allowing to probe the growth of spatial non-uniformities in the shock apex. These results are compared with experiments looking at counter-propagating shocks, showing a symmetric drive which leads to a collision and stagnation from $sim$40 ns onward. We present a preliminary comparison with numerical simulations with the radiation hydrodynamics code ARWEN, which provides expected plasma parameters for the design of future experiments in this facility.
The aim of this work is the investigation of the statistical properties of local electric fields in an ion-electron two component plasmas for coupled conditions. The stochastic fields at a charged or at a neutral point in plasmas involve both slow and fast fluctuation characteristics. The statistical study of these local fields based on a direct time average is done for the first time. For warm and dense plasma conditions, typically $N_{e}approx 10^{18}cm^{-3}$, $% T_{e}approx 1eV$, well controlled molecular dynamics (MD) simulations of neutral hydrogen, protons and electrons have been carried out. Relying on these textit{ab initio} MD calculations this work focuses on an analysis of the concepts of statistically independent slow and fast local field components, based on the consideration of a time averaged electric field. Large differences are found between the results of these MD simulations and corresponding standard results based on static screened fields. The effects discussed are of importance for physical phenomena connected with stochastic electric field fluctuations, e.g., for spectral line broadening in dense plasmas.
We present results from new experiments to study the dynamics of radiative shocks, reverse shocks and radiative precursors. Laser ablation of a solid piston by the Orion high-power laser at AWE Aldermaston UK was used to drive radiative shocks into a gas cell initially pressurised between $0.1$ and $1.0 bar$ with different noble gases. Shocks propagated at {$80 pm 10 km/s$} and experienced strong radiative cooling resulting in post-shock compressions of { $times 25 pm 2$}. A combination of X-ray backlighting, optical self-emission streak imaging and interferometry (multi-frame and streak imaging) were used to simultaneously study both the shock front and the radiative precursor. These experiments present a new configuration to produce counter-propagating radiative shocks, allowing for the study of reverse shocks and providing a unique platform for numerical validation. In addition, the radiative shocks were able to expand freely into a large gas volume without being confined by the walls of the gas cell. This allows for 3-D effects of the shocks to be studied which, in principle, could lead to a more direct comparison to astrophysical phenomena. By maintaining a constant mass density between different gas fills the shocks evolved with similar hydrodynamics but the radiative precursor was found to extend significantly further in higher atomic number gases ($sim$$4$ times further in xenon than neon). Finally, 1-D and 2-D radiative-hydrodynamic simulations are presented showing good agreement with the experimental data.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
