Neon is the fifth most abundant element and is found in the interior of stars and gas giant planets. Neon's noble, atomic fluid nature and large bandgap makes it an excellent candidate for comparison of experiment and theory at extreme conditions. We performed a combined computational and experimental study on shock compressed cryogenic liquid neon. Experiments at the Omega laser facility measured the principal Hugoniot to 600 GPa and provided temperature data along the principal Hugoniot. Magnetically accelerated, plate impact experiments at Sandia's Z machine demonstrate consistent results with the laser-driven data and emphasize the importance of using well-characterized impedance matching standards on the two experimental platforms. Additionally, density functional theory based molecular dynamics simulations reproduced the experimental Hugoniot data up to 500 GPa. We developed a new neon equation of state model based on the combined experimental data and simulation results at extreme conditions. This new equation of state significantly improves our understanding of the high pressure properties of neon compared to legacy models.

Helium or neopentane can be used as surrogate gas fill for deuterium (D2) or deuterium-tritium (DT) in laser-plasma interaction studies. Surrogates are convenient to avoid flammability hazards or the integration of cryogenics in an experiment. To test the degree of equivalency between deuterium and helium, experiments were conducted in the Pecos target chamber at Sandia National Laboratories. Observables such as laser propagation and signatures of laser-plasma instabilities (LPI) were recorded for multiple laser and target configurations. It was found that some observables can differ significantly despite the apparent similarity of the gases with respect to molecular charge and weight. While a qualitative behaviour of the interaction may very well be studied by finding a suitable compromise of laser absorption, electron density, and LPI cross sections, a quantitative investigation of expected values for deuterium fills at high laser intensities is not likely to succeed with surrogate gases.

Helium (He) plays a critical role in numerous areas ranging from the study of celestial objects like brown dwarfs and gas giants to modern-day technologies like nuclear energy and rocket propulsion. For many of these applications, it is essential to have a reliable equation of state (EOS) for He that yields an accurate representation of its thermodynamic behavior. To help constrain and develop such EOS models, we have performed a series of shock-compression experiments on cryogenic liquid He to pressures exceeding 100 GPa using a magnetically accelerated flyer plate on Sandia National Laboratories' Z-machine. We have also performed quantum molecular dynamics simulations that are consistent with our shock measurements. None of the previously available EOSs agree with our experimental and simulation results, motivating the development of a fluid-phase He EOS that we present in this study. We show that our EOS yields good agreement with published data that span temperatures and pressures encountered across a diverse array of applications.

the density resolution lower limits of the DI. Initial testing of the DI has demonstrated line-average electron density measurements within 9% of results acquired via a 94 GHz mm wave interferometer for line densities of ∼1 × 1014 cm−2, despite significant differences in probe beam geometries. The instrument will next be utilized for measurements on a ∼1 MA-scale pulsed power driver {MYKONOS [N. Bennett et al., Phys. Rev. Accel. Beams 22, 120401 (2019)] at SNL} before finally being deployed on SNL’s Z machine. The close electrode spacing (mm scale) on Z requires probe beam sizes of ∼1 mm, which can only be obtained with visible or near infrared optical systems, as opposed to longer wavelength mm wave systems that would normally be chosen for this range of density.

Zambian rivers belong to two major drainages: the Luapula-Congo and the Zambezi River system. Tectonic activity repeatedly altered drainage systems in Africa, so that current fish faunas can only be understood in the context of historic drainage capture events. We use phylogenetic relationships of one widespread lineage of haplochromine cichlids, the serranochromines, to trace their biogeographic expansion and diversification in Zambia. The mitochondrial DNA phylogeny suggests five ancient clades, and their common ancestor was likely to have invaded from the Lower Congo River. The branching intervals in the linearized tree analysis suggest three major cladogenesis events and two periods of faunal exchange. The five clades originating in the Congo River drainage diversified further; one stayed in the Congo drainage, one diversified in the Zambezi system only, while the three clades of mixed distribution underwent diversification in the Zambezi system, to re-enter the Congo drainage very recently, as indicated by sometimes zero mutation differences among taxa from different drainages. Our hypothesis is consistent with the suggested radiation in the extinct Lake palaeo-Makgadikgadi, so that we propose that the Zambian serranochromine fauna in part represents survivors of the extinct lacustrine flock plus several novel species that originated in situ.

the density resolution lower limits of the DI. Initial testing of the DI has demonstrated line-average electron density measurements within 9% of results acquired via a 94 GHz mm wave interferometer for line densities of ∼1 × 1014 cm−2, despite significant differences in probe beam geometries. The instrument will next be utilized for measurements on a ∼1 MA-scale pulsed power driver {MYKONOS [N. Bennett et al., Phys. Rev. Accel. Beams 22, 120401 (2019)] at SNL} before finally being deployed on SNL’s Z machine. The close electrode spacing (mm scale) on Z requires probe beam sizes of ∼1 mm, which can only be obtained with visible or near infrared optical systems, as opposed to longer wavelength mm wave systems that would normally be chosen for this range of density.

New Mexico to quantify the density resolution lower limits of the DI. Initial testing of the DI has demonstrated line-average electron density measurements within 9% of results acquired via a 94 GHz mm wave interferometer for line densities of ∼1 × 10 14 cm −2 , despite significant differences in probe beam geometries. The instrument will next be utilized for measurements on a ∼1 MA-scale pulsed power driver {MYKONOS [N. Bennett et al., Phys. Rev. Accel. Beams 22, 120401 (2019)] at SNL} before finally being deployed on SNL’s Z machine. The close electrode spacing (mm scale) on Z requires probe beam sizes of ∼1 mm, which can only be obtained with visible or near infrared optical systems, as opposed to longer wavelength mm wave systems that would normally be chosen for this range of density.

Forsterite (Mg 2 SiO 4 ) single crystals were shock compressed to pressures between 200 and 950 GPa using independent plate‐impact steady shocks and laser‐driven decaying shock compression experiments. Additionally, we performed density functional theory‐based molecular dynamics to aid interpretation of the experimental data and to investigate possible phase transformations and phase separations along the Hugoniot. We show that the experimentally obtained Hugoniot cannot distinguish between a pure liquid Mg 2 SiO 4 and an assemblage of solid MgO plus liquid magnesium silicate. The measured reflectivity is nonzero and increases with pressure, which implies that the liquid is a poor electrical conductor at low pressures and that the conductivity increases with pressure.