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Crystal structure and equation of state of Fe-Si alloys at super-Earth core conditions
The high-pressure behavior of Fe alloys governs the interior structure and dynamics of super-Earths, rocky extrasolar planets that could be as much as 10 times more massive than Earth. In experiments reaching up to 1300 GPa, we combine laser-driven dynamic ramp compression with in situ x-ray diffraction to study the effect of composition on the crystal structure and density of Fe-Si alloys, a potential constituent of super-Earth cores. We find that Fe-Si alloy with 7 weight % (wt %) Si adopts the hexagonal close-packed structure over the measured pressure range, whereas Fe-15wt%Si is observed in a body-centered cubic structure. This study represents the first experimental determination of the density and crystal structure of Fe-Si alloys at pressures corresponding to the center of a ~3–Earth mass terrestrial planet. Our results allow for direct determination of the effects of light elements on core radius, density, and pressures for these planets
Crystal structure and equation of state of Fe-Si alloys at super-Earth core conditions
The high-pressure behavior of Fe alloys governs the interior structure and dynamics of super-Earths, rocky extrasolar planets that could be as much as 10 times more massive than Earth. In experiments reaching up to 1300 GPa, we combine laser-driven dynamic ramp compression with in situ x-ray diffraction to study the effect of composition on the crystal structure and density of Fe-Si alloys, a potential constituent of super-Earth cores. We find that Fe-Si alloy with 7 weight % (wt %) Si adopts the hexagonal close-packed structure over the measured pressure range, whereas Fe-15wt%Si is observed in a body-centered cubic structure. This study represents the first experimental determination of the density and crystal structure of Fe-Si alloys at pressures corresponding to the center of a ~3–Earth mass terrestrial planet. Our results allow for direct determination of the effects of light elements on core radius, density, and pressures for these planets
Effects of fuel-capsule shimming and drive asymmetry on inertial-confinement-fusion symmetry and yield
Three orthogonal proton emission imaging cameras were used to study the 3D effects of low-mode drive asymmetries and target asymmetries on nuclear burn symmetry and yield in direct-drive, inertial-confinement-fusion experiments. The fusion yield decreased quickly as the burn region became asymmetric due to either drive or capsule asymmetry. Measurements and analytic scaling are used to predict how intentionally asymmetric capsule shells could improve performance by compensating for drive asymmetry when it cannot be avoided (such as with indirect drive or with polar direct drive).United States. Department of Energy (Grant DE-NA0002726)United States. Department of Energy (Grant DE-NA0002949
Response to Comment on "Insulator-metal transition in dense fluid deuterium"
International audienceIn their comment, Desjarlais et al. claim that a small temperature drop occurs after isentropic compression of fluid deuterium through the first-order insulator-metal transition. We show that their calculations do not correspond to the experimental thermodynamic path, and that thermodynamic integrations with parameters from first-principles calculations produce results in agreement with our original estimate of the temperature drop
Analysis of laser shock experiments on precompressed samples using a quartz reference and application to warm dense hydrogen and helium
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.Comment: 13 pages, 16 figures, 4 table