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.

The Chicxulub asteroid impact triggered mass extinction, mega-tsunamis and a spell of global warming that lasted for around 100,000 years. Although the recent Double Asteroid Redirection Test mission by NASA demonstrated that near-Earth objects can be successfully targeted, deflecting the most dangerous asteroids will require energy concentrations akin to nuclear explosions. However, targets suitable for practice missions are scarce. Here we demonstrate the simulation of asteroid deflection with an X-ray pulse from a dense argon plasma generated at the Z machine, a pulsed power device at Sandia National Laboratories. We use so-called X-ray scissors to place surrogate asteroidal material into free space, simultaneously severing supports and vapourizing the target surface. The ensuing explosion accelerates the mock asteroidal material in a scaled asteroid intercept mission. Deflection velocities of around 70 m s-1 for silica targets agree with radiation-hydrodynamic model predictions. We scale these results to proposed interceptor energies and predict that asteroids up to a diameter of (4 +/- 1) km can be deflected with this mechanism, showing a viable way to prepare for future planetary defence missions. Deflection is one of the options discussed for preventing catastrophic collisions of asteroids with Earth. Now, a megajoule-class X-ray pulse is used to simulate such scenarios, demonstrating that it is a viable strategy at higher interceptor energies.

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.

Sapphire (Al2O3) is a major constituent of the Earth's mantle and has significant contributions to the field of high-pressure physics. Constraining its Hugoniot over a wide pressure range and identifying the location of shock-driven phase transitions allows for development of a multiphase equation of state and enables its use as an impedance-matching standard in shock physics experiments. Here, we present measurements of the principal Hugoniot and sound velocity from direct impact experiments using magnetically launched flyers on the Z machine at Sandia National Laboratories. The Hugoniot was constrained for pressures from 0.2-2.1 TPa and a four-segment piecewise linear shock-velocity-particle-velocity fit was determined. First-principles molecular dynamics simulations were conducted and agree well with the experimental Hugoniot. Sound-speed measurements identified the onset of melt between 450 and 530 GPa, and the Hugoniot fit refined the onset to 525 +/- 13 GPa. A phase diagram which incorporates literature diamond-anvil cell data and melting measurements is presented.

Argon is the most abundant noble gas on Earth and its noble, atomic fluid nature 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 argon. Using Sandia's Z machine, we shock compressed liquid argon to 600 GPa and reshock states up to 950 GPa. Laser shock experiments at the Omega Laser facility extend the principal Hugoniot to 1000 GPa and provided temperature data along the principal Hugoniot. The plate impact experiments and laser shock experiments used well-characterized impedance matching standards and demonstrate consistent results between the two platforms over a common range. Density functional theory based molecular dynamics simulations provided additional data on the Hugoniot to 600 GPa. The combined experimental data and simulation results provide constraints on the development of new equation of state models at extreme conditions.

determine the silicate solubility and metal-silicate partitioning behavior of W, including its concomitant oxidation state. However, results of previous studies (Fig. 1) are inconsistent on whether W occurs as W4+ or W{sup 6+}. It is assumed that W{sup 4+} is the cation valence relevant to core formation. Given the sensitivity to silicate composition of high valence cations, knowledge of the oxidation state of W over a wide range of fO{sub 2} is critical to understanding the oxidation state of the mantle and core formation processes. This study seeks to measure the W valence and change in valence state over the range of fO{sub 2} most relevant to core formation, around IW-2.

Lattice and electronic structure interactions for f-electrons are fundamental challenges for lanthanide equation of state development. Difficulties in first-principles calculations, such as density functional theory (DFT), emphasize the need for well-characterized experimental data. Here, we measure in-situ x-ray diffraction of shocked samarium (Sm) and temperature along the Hugoniot for the first time, providing direct evidence for phase transitions. We report direct evidence of a distorted fcc (dfcc) phase at 23 GPa. Shocked samarium melts from the dfcc phase starting at 33 GPa (1333 K), with complete melt at 40 GPa (1468 K). Previous work indicated shock melt at 27 GPa (1200 K), underscoring the significance of x-ray measurements for detecting phase transitions. Interestingly, our observed melting is in sharp contrast with the melting reported by a diamond anvil cell study. These experimental data can tightly constrain first principles calculations and serve as key touchstones for equation of state modeling.