Predictions of x-ray scattering spectra for warm dense matter

Souza, Andre N.; Perkins, David J.; Starrett, C. E.; Saumon, D.; Hansen, Stephanie B.

doi:10.1103/physreve.89.023108

Cited by 48 publications

(51 citation statements)

References 33 publications

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“…These results differ from recently published structure factors 23,24 . Furthermore, our experimental and computational findings using DFT-MD are precise enough to allow for the direct calculation of macroscopic material properties.…”

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confidence: 85%

Ultrabright X-ray laser scattering for dynamic warm dense matter physics

et al. 2015

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In megabar shock waves, materials compress and undergo a phase transition to a dense charged-particle system that is dominated by strong correlations and quantum effects. This complex state, known as warm dense matter, exists in planetary interiors and many laboratory experiments (for example, during high-power laser interactions with solids or the compression phase of inertial confinement fusion implosions). Here, we apply record peak brightness X-rays at the Linac Coherent Light Source to resolve ionic interactions at atomic (ångström) scale lengths and to determine their physical properties. Our in situ measurements characterize the compressed lattice and resolve the transition to warm dense matter, demonstrating that short-range repulsion between ions must be accounted for to obtain accurate structure factor and equation of state data. In addition, the unique properties of the X-ray laser provide plasmon spectra that yield the temperature and density with unprecedented precision at micrometre-scale resolution in dynamic compression experiments. M aterials exposed to high pressures of 1 Mbar and above have recently been the subject of increased attention due to their importance for the physics of planetary formation 1-3 , for material science 4 and for inertial confinement fusion research 5 . The behaviour of shock-compressed aluminium is of particular interest because it has been proposed as a standard for shock-wave experiments 6 and is widely used for equation-of-state 7,8 and warm dense matter (WDM) 9,10 studies. At room temperature, aluminium has three delocalized electrons, so it provides a prototype for an ideal electron fluid. As temperatures and pressures increase, compressing and breaking ionic lattice bonds, strong ionic forces remain, resulting in significant deviations from a simple fluid.Simulations using density functional theory coupled to manyparticle molecular dynamics (DFT-MD) have evolved into an ab initio tool to explore this regime of high-pressure physics 11,12 . To date, these simulations have been used to predict physical properties derived from optical observations of particle and shock velocities. Studies of structural properties that are sensitive to many-particle electron-ion and ion-ion interaction physics 13 have been challenging 14 , although recent progress has been made using X-ray absorption spectroscopy 15,16 . Early experiments on fourth-generation light sources 17 have made use of X-ray diffraction and measured the structural evolution from elastic to plastic states 18 . However, pressures in the Mbar regime, as required for melting many solids, have only recently become available at the Matter in Extreme Conditions (MEC) instrument at the Linac Coherent Light Source (LCLS).Here we visualize, for the first time, the evolution of compressed matter across the melting line and the coexistence regime into a WDM state. The combination of high-power optical lasers and the X-ray beam at MEC provides high-resolution X-ray scattering at multi-Mbar pressures. Our data provide the io...

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Ultrabright X-ray laser scattering for dynamic warm dense matter physics

et al. 2015

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“…Lastly, we present an application of the model to CH 1. 36 and compare the resulting electronic and ionic structures to OFMD and…”

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confidence: 99%

Integral equation model for warm and hot dense mixtures

et al. 2014

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In Starrett and Saumon [Phys. Rev. E 87, 013104 (2013)] a model for the calculation of electronic and ionic structures of warm and hot dense matter was described and validated. In that model the electronic structure of one 'atom' in a plasma is determined using a density functional theory based average-atom (AA) model, and the ionic structure is determined by coupling the AA model to integral equations governing the fluid structure. That model was for plasmas with one nuclear species only. Here we extend it to treat plasmas with many nuclear species, i.e. mixtures, and apply it to a carbon-hydrogen mixture relevant to inertial confinement fusion experiments. Comparison of the predicted electronic and ionic structures with orbital-free and Kohn-Sham molecular dynamics simulations reveals excellent agreement wherever chemical bonding is not significant.

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“…The sum of the two contributions at the origin yields the total number of electrons Z. The comparison with the average atom results of Souza [11] is shown in Fig. 2.…”

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Evidence for out-of-equilibrium states in warm dense matter probed by x-ray Thomson scattering

et al. 2015

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A recent and unexpected discrepancy between ab initio simulations and the interpretation of a laser shock experiment on aluminum, probed by X-ray Thomson scattering (XRTS), is addressed.The ion-ion structure factor deduced from the XRTS elastic peak (ion feature) is only compatible with a strongly coupled out-of-equilibrium state. Orbital free molecular dynamics simulations with ions colder than the electrons are employed to interpret the experiment. The relevance of decoupled temperatures for ions and electrons is discussed. The possibility that it mimics a transient, or metastable, out-of-equilibrium state after melting is also suggested.

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Predictions of x-ray scattering spectra for warm dense matter

Cited by 48 publications

References 33 publications

Ultrabright X-ray laser scattering for dynamic warm dense matter physics

Ultrabright X-ray laser scattering for dynamic warm dense matter physics

Integral equation model for warm and hot dense mixtures

Evidence for out-of-equilibrium states in warm dense matter probed by x-ray Thomson scattering

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