Bulletin of the American Physical Society
63rd Annual Meeting of the APS Division of Plasma Physics
Volume 66, Number 13
Monday–Friday, November 8–12, 2021; Pittsburgh, PA
Session PI01: High Energy Density Experiment, Modeling, and TheoryInvited Live
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Chair: Tom White, University of Nevada - Reno Room: Ballroom B |
Wednesday, November 10, 2021 2:00PM - 2:30PM |
PI01.00001: Symmetric theory of heat and magnetic transport in a collisional magnetized plasma Invited Speaker: James D Sadler Braginskii extended-magnetohydrodynamics (XMHD) is used to model the effect of magnetic fields on the hydrodynamics of high energy density plasmas. This theory is a central modelling capability for hohlraums, Z-pinches, laser ablation fronts, magnetized inertial confinement fusion concepts, fast ignition, and certain astrophysical settings. Even if the magnetic field has a pressure far less than the plasma pressure, it can still indirectly affect hydrodynamics by insulating and deflecting the heat flux. This is described by the transport coefficients, found from kinetic theory. In XMHD codes, these are calculated at each timestep using a fit to the results of kinetic simulations. We present a re-worked formulation of Braginskii's original equations, explicitly demonstrating the symmetry between heat flux and magnetic field advection in the plasma. We show that, although superficially accurate, commonly used fit functions [e.g. Epperlein and Haines, Phys. Fluids (1986)] cannot correctly reproduce this theoretical symmetry. This means that XMHD simulations in the literature, using codes such as Gorgon and Hydra, have produced incorrect and discontinuous magnetic field profiles. We have implemented corrected fit functions into the Gorgon code. This resolves discrepancies with the results of two-dimensional fully kinetic simulations. We explore the interpretation of each XMHD term in relation to high energy density experiments and instabilities such as Kelvin-Helmholtz induced mixing. |
Wednesday, November 10, 2021 2:30PM - 3:00PM |
PI01.00002: Probing a new regime of chemistry at HED conditions: Na as a prototypical example Invited Speaker: Danae N Polsin At high-energy-density (HED) conditions, a new realm of quantum behavior emerges. Examples at extreme HED compression include electron localization, structural complexity, core electron chemistry, and more. Sodium is an ideal prototype material to explore such behavior as it is so compressible, we can squeeze sodium to the point where core orbitals overlap at modest HED pressures. At 200 GPa, Na transforms from a simple free-electron metal to a structurally complex topological insulator. This phase is due to the electrons, which typically fill the Fermi Sea, instead being driven into interstitial positions due to the density-driven quantum mechanical constraints on the electronic wave functions. We report the structural and electronic properties of Na at the most extreme compressions yet studied, where the interatomic spacing approaches the Na+ ionic diameter and exceeds the 3s orbital diameter. Using lasers as the high-pressure driver, x-ray diffraction measurements to 480 GPa and 2000 K reveal unexpected new phases. Simultaneous reflectivity measurements suggest a dramatic drop in the conductivity of both the solid and dense liquid phases, where theory predicts the dense liquid undergoes a continuous transition from free electron to one where electrons are trapped in bubbles within the Na+ fluid. These data together with recent density functional theory calculations are consistent with the emergence of high-temperature “insulating plasma” states at extreme compression. I will discuss thoughts on how general this new phase of matter might be, as well as potential implications for such chemistry in the deep interiors of planets and stars throughout the universe. |
Wednesday, November 10, 2021 3:00PM - 3:30PM |
PI01.00003: On the application of plasma kinetic theory to electron-ion transport in warm dense matter Invited Speaker: Shane Rightley Modern astrophysics and laboratory experiments push plasma physics into regimes beyond the limits of its established microscopic theories. This talk concerns extending these limits to encompass plasmas that are subject to moderate Coulomb correlations in addition to electron degeneracy. This parameter regime is called warm dense matter (WDM). Recent high-fidelity ab initio computational models have proven effective in predicting properties of WDM but the computational expense prohibits the exploration of large parameter spaces. Here, we demonstrate a new method for calculating transport in WDM that balances ease of evaluation with physical fidelity. The method generalizes the recently developed mean force kinetic theory [S. D. Baalrud and J. Daligault, Phys. Plasmas 26, 082106 (2019)] to treat the quantum statistics and dynamics of electrons under WDM conditions. The convergent quantum kinetic equation developed and applied here is highly analogous to the quantum Boltzmann equation of Uehling and Uhlenbeck, but with the effect of strong coupling incorporated through the scattering potential, which is the potential of mean force obtained from equilibrium quantum statistical mechanics. Focusing on ion-electron collisions, we apply the model to predict temperature and momentum relaxation, the e-i contribution to electrical conductivity, and the stopping power of fully ionized ions in warm dense deuterium. We select a density and range of temperatures to span classical and weakly coupled to degenerate and moderately coupled conditions and find that the model shows promising agreement with ab initio simulations. To conclude we discuss the limitations, possible improvements, and additional applications of the theory. |
Wednesday, November 10, 2021 3:30PM - 4:00PM |
PI01.00004: Novel convergent hydrodynamic instability experiments on Z Invited Speaker: David A Yager-Elorriaga Hydrodynamic instabilities are critically important for a variety of physical phenomenon. In astrophysics, the Rayleigh-Taylor (RT) and Richtmyer-Meshkov (RM) instabilities can break the spherical symmetry in supernovae explosions and the associated mixing can enable the synthesis of heavy and intermediate mass elements. In inertial confinement fusion, they impact the confining ability of the tamper and mix impurities into the hot fuel, ultimately degrading the thermonuclear fusion production. |
Wednesday, November 10, 2021 4:00PM - 4:30PM |
PI01.00005: Metastability of diamond ramp-compressed to 2 terapascals Invited Speaker: Amy E Lazicki Carbon is the fourth most prevalent element in the universe and essential for all known life. In the elemental form it is found in multiple allotropes including graphite, diamond, and fullerenes, and it has long been predicted that even more structures can exist at greater than Earth-core pressures. Several new phases have been predicted in the multi-terapascal (TPa) regime, important for accurately modeling interiors of carbon-rich exoplanets. By compressing solid carbon to 2 TPa (20 million atmospheres; over 5 times the pressure at the Earth's core) using ramp-shaped laser pulses, and simultaneously measuring nanosecond-duration time resolved x-ray diffraction, we found that solid carbon retains the diamond structure far beyond its regime of predicted stability. The results confirm predictions that the strength of the tetrahedral molecular orbital bonds in diamond persists under enormous pressure, resulting in large energy barriers that hinder conversion to the more stable high-pressure allotropes, just as graphite formation from metastable diamond is kinetically hindered at atmospheric pressure. This work nearly doubles the record high pressure at which x-ray diffraction has been recorded on any material. [Lazicki, A., McGonegle, D., Rygg, J.R. et al. Metastability of diamond ramp-compressed to 2 terapascals. Nature 589, 532–535 (2021)] |
Wednesday, November 10, 2021 4:30PM - 5:00PM |
PI01.00006: Advancing the Accuracy of DFT Simulations for High-Energy-Density Plasmas by Developing Temperature-Dependent Exchange-Correlation Functional Invited Speaker: Valentin Karasiev Ab initio molecular dynamics simulations based on the free-energy density functional theory (DFT) has proven to be a successful and key tool to understand warm dense matter (WDM) and high-energy-density (HED) plasmas. DFT requires approximations for the exchange-correlation (XC) energy density functional, which effectively takes into account many-body interaction effects. Currently, vast majority of DFT simulations of WDM and HED plasmas use the ground-state XC functionals without explicit temperature dependence, leading to inaccuracy in the regime of T/TF~0.5. In this talk we discuss development of XC density functionals with explicit temperature dependence based on rigorous constraints [1-3]. A simple but accurate scheme is implemented via universal additive thermal correction to XC using a perturbative-like self-consistent approach. The additive correction with explicit temperature dependence is applied to the ground-state deorbitalized strongly constrained and appropriately normed (SCAN-L) meta-GGA XC leading to thermal XC functional denoted as T-SCAN-L [4]. Incorporation of exact finite-temperature constraints makes functional accurate and broadly predictive over the entire temperature range. The T-SCAN-L meta-GGA functional shows significant improvement of accuracy for WDM and HED plasma simulations, when compared to traditional XC functionals, as demonstrated by the comparison to the reference path-integral Monte Carlo simulations for deuterium and helium equation of states. The T-SCAN-L calculations show good agreement with experimental measurements of the deuterium principal Hugoniot in the regime of maximum compression and sound speed. Direct current conductivity of warm-dense aluminum also gives better agreement with experiments over other XC functionals such as PBE and SCAN-L. |
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