S. H. Glenzer

We report on a theoretical model for the calculation of x-ray scattering from high-pressure electrides. By treating interstitial electrons as effective anions forming a sublattice within the crystal, we explicitly account for Bragg reflections from the sublattice as well as for scattering interferences between the ion lattice and the anion sublattice. The additional reflections and interferences lead to significant modifications of the static structure factor as compared to the pure lattices. Our results are important for accurate calculations of material properties in the high-pressure phase and allow for direct experimental verification of electride phases in matter at ultrahigh pressures through angle-resolved x-ray scattering.

DOI:https://doi.org/10.1103/PhysRevE.83.059905

The introduction of brilliant free-electron lasers enables new pump-probe experiments to characterize warm dense matter states. For instance, a short-pulse optical laser irradiates a liquid hydrogen jet that is subsequently probed with brilliant soft x-ray radiation. The strongly inhomogeneous plasma prepared by the optical laser is characterized with particle-in-cell simulations. The interaction of the soft x-ray probe radiation for different time delays between pump and probe with the inhomogeneous plasma is also taken into account via radiative hydrodynamic simulations. We calculate the respective scattering spectrum based on the Born-Mermin approximation for the dynamic structure factor considering the full density and temperature-dependent Thomson scattering cross section throughout the target. We can identify plasmon modes that are generated in different target regions and monitor their temporal evolution. Therefore, such pump-probe experiments are promising tools not only to measure the important plasma parameters density and temperature but also to gain valuable information about their time-dependent profile through the target. The method described here can be applied to various pump-probe scenarios by combining optical lasers and soft x ray, as well as x-ray sources.

Ignition Set to Go: One aim of the National Ignition Facility is to implode a capsule containing a deuterium-tritium fuel mix and initiate a fusion reaction. With 192 intense laser beams focused into a centimeter-scale cavity, a major challenge has been to create a symmetric implosion and the necessary temperatures within the cavity for ignition to be realized (see the Perspective by Norreys ). Glenzer et al. (p. 1228 , published online 28 January) now show that these conditions can be met, paving the way for the next step of igniting a fuel-filled capsule. Furthermore, Li et al. (p. 1231 , published online 28 January) show how charged particles can be used to characterize and measure the conditions within the imploding capsule. The high energies and temperature realized can also be used to model astrophysical and other extreme energy processes in a laboratory settings.

Recent developments of dynamic x-ray characterization experiments of dense matter are reviewed, with particular emphasis on conditions relevant to interiors of terrestrial and gas giant planets. These studies include characterization of compressed states of matter in light elements by x-ray scattering and imaging of shocked iron by radiography. Several applications of this work are examined. These include the structure of massive “super-Earth” terrestrial planets around other stars, the 40 known extrasolar gas giants with measured masses and radii, and Jupiter itself, which serves as the benchmark for giant planets.