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We present the development of a pulsed power experimental technique to infer the electrical conductivity of metals from ambient to high energy density conditions. The method is implemented on Thor, a moderate scale (1–2 MA) pulsed power driver. The electrical conductivity of copper at elevated temperature (>4000 K) and pressure (>10 GPa) is determined, and a new tabular material model is developed, guided by density functional theory, which preserves agreement with existing experimental data. Minor modifications (<10%) are found to be necessary to the previous Lee–More–Desjarlais model isotherms in the vicinity of the melt transition in order to account for observed discrepancies with the new experimental data. An analytical model for magnetic direct drive flyer acceleration and Joule heating induced vaporization based on the Tsiolkovsky "rocket equation" is presented to assess sensitivity of the method to minor changes in electrical conductivity. [ABSTRACT FROM AUTHOR]

We present a comprehensive study of transport coefficients including DC electrical conductivity and related optical properties, electrical contribution to the thermal conductivity, and the shear viscosity via ab initio molecular dynamics and density functional theory calculations on the "priority 1" cases from the "Second Charged-Particle Transport Coefficient Workshop" [Stanek et al., Phys. Plasmas (to be published 2024)]. The purpose of this work is to carefully document the entire workflow used to generate our reported transport coefficients, up to and including our definitions of finite size and statistical convergence, extrapolation techniques, and choice of thermodynamic ensembles. In pursuit of accurate optical properties, we also present a novel, simple, and highly accurate algorithm for evaluating the Kramers–Kronig relations. These heuristics are often not discussed in the literature, and it is hoped that this work will facilitate the reproducibility of our data. [ABSTRACT FROM AUTHOR]

We present density functional theory (DFT) simulations and shock-reshock experiments for liquid carbon dioxide (CO2) in the range 100 to 800 GPa. The simulations support the previously suggested dissociation threshold around 50 GPa [W. J. Nellis et al., J. Chem. Phys. 95, 5268 (1991)] for shocked liquid CO2 and describe a very steep Hugoniot past dissociation. We performed the shock-reshock experiments using the Sandia Z machine. The Z machine magnetically accelerated aluminum flyer plates to shock compress cryogenic liquid CO2 to 550 GPa and attained reshock states up to 840 GPa. The plate impact experiments combined with well-characterized impedance matching standards and laser velocimetry results in high-accuracy measurements of the principal Hugoniot and reshock states of liquid CO2. The experimental results validated the DFT simulations at extreme conditions and the combination of experiment and DFT provide reliable data for evaluating existing and constructing future wide-range equations of state models for molecular compounds such as CO2. [ABSTRACT FROM AUTHOR]

The equation of state (EOS) of bulk niobium (Nb) was investigated within the framework of density functional theory, with Mermin's generalization to finite temperatures. The shock Hugoniot for fully-dense and porous Nb was obtained from canonical ab initio molecular dynamics simulations with Erpenbeck's approach based on the Rankine-Hugoniot jump conditions. The phase space was sampled along isotherms between 300 and 4000 K, for densities ranging from ρ = 5.5 to 12 g/cm 3. Results from simulations compare favorably with room-temperature multianvil and diamond anvil cell data for fully-dense Nb samples and with a recent tabulated SESAME EOS. The results of this study indicate that, for the application of weak and intermediate shocks, the tabular EOS models are expected to give reliable predictions. [ABSTRACT FROM AUTHOR]

We report the results of the second charged-particle transport coefficient code comparison workshop, which was held in Livermore, California on 24–27 July 2023. This workshop gathered theoretical, computational, and experimental scientists to assess the state of computational and experimental techniques for understanding charged-particle transport coefficients relevant to high-energy-density plasma science. Data for electronic and ionic transport coefficients, namely, the direct current electrical conductivity, electron thermal conductivity, ion shear viscosity, and ion thermal conductivity were computed and compared for multiple plasma conditions. Additional comparisons were carried out for electron–ion properties such as the electron–ion equilibration time and alpha particle stopping power. Overall, 39 participants submitted calculated results from 18 independent approaches, spanning methods from parameterized semi-empirical models to time-dependent density functional theory. In the cases studied here, we find significant differences—several orders of magnitude—between approaches, particularly at lower temperatures, and smaller differences—roughly a factor of five—among first-principles models. We investigate the origins of these differences through comparisons of underlying predictions of ionic and electronic structure. The results of this workshop help to identify plasma conditions where computationally inexpensive approaches are accurate, where computationally expensive models are required, and where experimental measurements will have high impact. [ABSTRACT FROM AUTHOR]

We present new equations of state (EOS) for polymethylmethacrylate and its shock-driven decomposition products, generated in both tabular form and as linear U S − u p fits to all previously available shock data. Different approaches are taken for materials shocked above and below the apparent threshold for chemical reactions at pressures P ≈ 30 GPa. Both EOSs are calibrated to and compared with a broad array of experimental results, as well as new ab initio molecular dynamics simulations presented here. Comparisons are good in most cases, and we focus our particular attention on those observables that test the distinction between reactants and products. [ABSTRACT FROM AUTHOR]

Hypervelocity impact‐driven vaporization is characteristic of late‐stage planet formation. Yet the behavior and properties of liquid‐vapor mixtures of planetary materials of interest are typically unknown. Multiphase equations of state used in hydrodynamic simulations of planet impacts therefore lack reliable data for this important phenomenon. Here, we present the first constraints on the liquid‐vapor critical point and coexistence phase boundary of Mg2SiO4 computed from ab initio molecular dynamics simulations. We found that the vapor is depleted in magnesium and enriched in silica and oxygen, while the coexisting liquid is enriched in magnesium and depleted in oxygen, from which we infer vaporization is incongruent. The critical point was estimated from an equation of state fit to the data. The results are in line with recent calculations of MgSiO3 and together confirm that extant multiphase equation of state (EOS) models used in planetary accretion modeling significantly underestimate the amount of supercritical material postimpact. Key Points: Mg2SiO4 vaporizes incongruently and produces Mg‐poor vapor and O2 and SiO‐enriched vaporCritical point occurs at lower density and temperature than commonly used multiphase EOSGiant impact simulations underestimate amount of supercritical material postimpact [ABSTRACT FROM AUTHOR]

ALEGRA is a multiphysics finite-element shock hydrodynamics code, under development at Sandia National Laboratories since 1990. Fully coupled multiphysics capabilities include transient magnetics, magnetohydrodynamics, electromechanics, and radiation transport. ALEGRA is used to study hypervelocity impact, pulsed power devices, and radiation effects. The breadth of physics represented in ALEGRA is outlined here, along with simulated results for a selected hypervelocity impact experiment. • ALEGRA is a multiphysics finite-element shock hydrodynamics code. • An ALEGRA simulation captures phenomenology from a previous gas gun experiment. • Multiphysics capabilities include electromagnetics and radiation transport. • A multiphysics simulation demonstrates electromagnetic induction during impact. [ABSTRACT FROM AUTHOR]

Nested stainless steel wire array variations were investigated on the 20 MA Z machine [R. B. Spielman et al., Phys. Plasmas 5, 2105 (1998)]. In order to reach experimentally observed electron temperatures near 3.8 keV and excite the K shell, these ∼6.7 keV photon energy x-ray sources must be of large initial diameter (45–80 mm) which poses a concern for magnetic Rayleigh–Taylor instability growth. We discuss the implosion dynamics in these large diameter wire arrays, including an analysis of the ablation phase indicating that the prefill material is snowplowed at large radius. Nested array configurations with various mass and radius ratios are compared for instability mitigation and K-shell scaling. Degradation of the K-shell x-ray power and yield was observed for shots that did not have simultaneous implosion of the outer and inner wire arrays. Shots that were designed per this constraint exhibited K-shell yield scaling consistent with the model of J. W. Thornhill et al. [IEEE Trans. Plasma Sci. 34, 2377 (2006)] which had been benchmarked to single array results. This lends confidence to K-shell yield predictions using this model for future shots on the refurbished Z machine. Initial results employing a triple nested wire array to stabilize the large diameter implosion are also reported. [ABSTRACT FROM AUTHOR]

Presented are the results from the liner ablation experiments conducted at 550 kA on the Michigan Accelerator for Inductive Z-Pinch Experiments. These experiments were performed to evaluate a hypothesis that the electrothermal instability (ETI) is responsible for the seeding of magnetohydrodynamic instabilities and that the cumulative growth of ETI is primarily dependent on the material-specific ratio of critical temperature to melting temperature. This ratio is lower in refractory metals (e.g., tantalum) than in non-refractory metals (e.g., aluminum or titanium). The experimental observations presented herein reveal that the plasma-vacuum interface is remarkably stable in tantalum liner ablations. This stability is particularly evident when contrasted with the observations from aluminum and titanium experiments. These results are important to various programs in pulsed-power-driven plasma physics that depend on liner implosion stability. Examples include the magnetized liner inertial fusion (MagLIF) program and the cylindrical dynamic material properties program at Sandia National Laboratories, where liner experiments are conducted on the 27-MA Z facility. [ABSTRACT FROM AUTHOR]