Bulletin of the American Physical Society
61st Annual Meeting of the APS Division of Plasma Physics
Volume 64, Number 11
Monday–Friday, October 21–25, 2019; Fort Lauderdale, Florida
Session NO7: HED: Warm Dense Matter |
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Chair: Gianluca Gregori, University of Oxford Room: Grand F |
Wednesday, October 23, 2019 9:30AM - 9:42AM |
NO7.00001: Dynamics of electrical conductivity and structure of warm dense aluminum probed by single-shot THz spectroscopy and electron diffraction Benjamin Ofori-Okai, Zhijiang Chen, Adrien Descamps, Mianzhen Mo, Xieyu Na, Lars Seipp, Xiaozhe Shen, Stephen Weathersby, Anthea Weinmann, Jie Yang, XIjie Wang, Siegfried Glenzer We used single-shot terahertz time-domain spectroscopy and mega-electron-volt ultrafast electron diffraction (MeV-UED) to study the electrical conductivity and structure of Warm Dense aluminum. By measuring changes in the THz field, we determine the conductivity of the WD-Al at different electron temperatures. We combine these results with studies using MeV-UED, which is ideally suited to probe of the structure of thin films because of the high scattering cross section, short wavelength, and sub-picosecond pulse duration of relativistic electron bunches. These measurements provide crucial characterization of the state and density of the WD-Al probed by the THz pulse, as well as the timescale of melting of Al films at high excitation densities. This work is supported by DOE Office of Science, Fusion Energy Science under FWP 100182, and the DOE BES Accelerator and Detector R{\&}D program. B. K. Ofori-Okai, Rev. Sci. Instrum. 89(10), 10D109 (2018) N. W. Ashcroft and N. D. Mermin, Solid State Physics, 1st ed. (Brooks/Cole, 1976) M. Z. Mo, Rev. Sci. Instrum. 87(11), 11D810 (2016) M. Z. Mo,* Z. Chen*, Science 360(6396), 1451--1455 (2018) [Preview Abstract] |
Wednesday, October 23, 2019 9:42AM - 9:54AM |
NO7.00002: Radiation transport modeling and preliminary UV spectroscopy measurements on expanded WDM Nicholas Ramey, James Colgan, Chris Fontes, Peter Hakel, Heidi Morris, Joshua Coleman, Ryan McBride, Ronald Gilgenbach Warm Dense Matter (WDM) is characterized by the strongly correlated nature of the ions in addition to the partially or fully Fermi degenerate electron population. An intense, relativistic electron pulse heats range-thin low-Z metal foils to WDM in a two-stage heating process. The Los Alamos suite of atomic physics codes [1] has been utilized to determine plasma parameters from the visible spectral range [2] but did not consider the strong density gradient and opacity. The FESTR code [3] is used as a spectral postprocessor of LASNEX hydrodynamic simulations to generate long wave UV synthetic spectra accounting for emission and absorption effects. A linear array of 19, 200-um fibers couple to a UV-sensitive ICCD camera and Czerny-Turner spectrometer to provide temporal and 1-D spatial resolution of the expanding plasma plume. The use of FESTR allows us to model temperature and density regimes that have not yet been quantified in expanded electron beam driven WDM. [1] C.J. Fontes et al., J. Phys. B 48, 144014 (2015). [2] J.E. Coleman and J. Colgan, Phys. Rev. E 96, 013208 (2017). [3] P. Hakel, Comp. Phys. Commun. 207, 415 (2016). [Preview Abstract] |
Wednesday, October 23, 2019 9:54AM - 10:06AM |
NO7.00003: Dynamic measurements of laser produced argon plasmas using high resolution X-ray Thomson scattering Luke Fletcher, Emma McBride, Bastian Witte, Siegfried Glenzer Ultra-bright coherent X-rays from the LCLS coupled with a novel micro-jet platform have enabled high resolution measurements of material properties via X-ray scattering with unprecedented dynamic range. Here we present X-ray scattering measurements from argon plasmas approaching temperatures of 200 eV. Non-resonant inelastic X-ray scattering from core, and free electrons, of ps-laser driven argon have allowed for direct measurements of the ionization, density, and temperature dynamics of the hot plasma created near the laser-material interface. Our results demonstrate the unique capability that X-ray lasers provide in order to gain detailed insights into previously unexplored regions of material phases in extreme environments. [Preview Abstract] |
Wednesday, October 23, 2019 10:06AM - 10:18AM |
NO7.00004: Mapping the Electronic Structure of Warm Dense Nickel via Resonant Inelastic X-ray Scattering Sam Vinko, Oliver Humphries, Alan Miscampbell, Quincy Van De Berg, Orlando Ciricosta, Muhammad Kasim, Ryan Royle, Justin Wark, Robin Marjoribanks, Hae Ja Lee, Eric Galtier, Bob Nagler The exploration of the quantum behaviour of high energy-density systems is a research area of broad importance to applications in plasma physics, astrophysics and fusion energy science. However, measuring the electronic structure in such systems remains a formidable experimental challenge, leading to a dearth of data of sufficient quality for benchmarking theoretical models in extreme plasma conditions. Resonant inelastic x-ray scattering (RIXS) is a popular experimental technique to study low-energy excitations in quantum systems, however, x-ray source requirements have so far limited its use to condensed matter systems. Here we show how the electronic structure of solid-density nickel heated to temperatures of 10’s of eV can be mapped via RIXS using the Linac Coherent Light Source free-electron laser at SLAC. We extract single-shot simultaneous measurements of electronic temperature, ionization, ionization potential depression, bound state energies and of the valence density of states. This technique provides a promising approach to observe directly electron relocalization as a function of the plasma environment for the first time. [Preview Abstract] |
Wednesday, October 23, 2019 10:18AM - 10:30AM |
NO7.00005: Measurements of Release-Isentropes of Isochorically Heated Warm Dense Matter on the OMEGA-EP Laser Alison Saunders, Amy Lazicki, Matt Hill, Joe Nilsen, Phil Sterne, Heather Whitley, Yuan Ping Understanding the equation of state (EOS) of materials at high pressures had broad relevance to astrophysical objects and laboratory experiments. An area in which the EOS is particularly difficult to model is the warm dense matter (WDM) regime, in which the standard plasma physics approximations do not apply, highlighting the need for experimental work. Experiments have been done to characterize the WDM Hugoniot [1], but measuring the material isentrope also can validate EOS models, as has been demonstrated on ramp-compressed solids and has been recently extended to WDM through measurements of isentropic release [2]. We present results from a platform developed for the OMEGA-EP laser from which the release isentrope of warm dense aluminum is measured. The sample is isochorically heated up to 10 eV by protons. Streaked x-ray radiography quantifies the density of the expanding material, which can be analyzed to obtain a pressure-density isentrope curve [3]. Streaked optical pyrometry constrains the temperature of the sample. Results from this platform will benchmark EOS models in the WDM regime. [1] T. Doeppner et al., Phys. Rev. Lett. 121, 025001 (2018). [2] D. Hoarty et al., HEDP 8, 50 (2012). [3] M. E. Foord et al., RSI 78, 2586 (2004). [Preview Abstract] |
Wednesday, October 23, 2019 10:30AM - 10:42AM |
NO7.00006: On the Relationship Between Line Broadening and Second-Order Transitions in Hot, Dense Plasmas Rory Baggott, Stuart Mangles, Steven Rose Recent measurements of opacity under solar conditions have suggested that widely-applied models may omit some key physics [Bailey et. al. 2015]. Subsequently, there has been interest in two-photon processes as a possible source of opacity [More et. al. 2017, Kruse and Iglesias 2019] and it has been suggested that two-photon absorption might be interpreted in terms of line broadening by background radiation. Likewise, the influence of electron collisions on absorption can be viewed either in terms of collisional line broadening or in terms of second-order electron-photon transitions. In this work, we examine the relationship between second-order transitions and existing treatments for line broadening and show that they share a common physical basis. This leads to the conclusion that two-photon and electron-photon processes cannot be considered in simple addition with existing calculations but should instead be thought of as an alternate limit for the line shape. Furthermore, this suggests a new approach to calculating opacity in windows between absorption lines. [Preview Abstract] |
Wednesday, October 23, 2019 10:42AM - 10:54AM |
NO7.00007: Quantum Kinetic Model for Dense Plasma Mixtures Jeff Haack, Cory Hauck, Michael Murillo A multitemperature Bhatnagar-Gross-Krook kinetic model is developed that includes partial degeneracy for the electrons. The model is constructed to satisfy the basic conservation laws with an H-theorem, generalized to mixed statistics (i.e., Maxwell-Boltzmann, Fermi-Dirac), that yields the desired equilibrium limit. From this model, we obtain a moment-based quantum hydrodynamics formulation closed through a Chapman-Enskog expansion to yield expressions for the transport coefficients, including electron-ion temperature relaxation and electronic thermal conductivity. The transport coefficients include both electron-electron and electron-ion collisions with degeneracy corrections valid from zero temperature to the classical limit. Comparisons are made with previous kinetic models for dense plasmas, and implications for modeling experiments are discussed. [Preview Abstract] |
Wednesday, October 23, 2019 10:54AM - 11:06AM |
NO7.00008: DFT-based Analytic Pair Interactions for Rapid Molecular Dynamics Simulations of Dense Plasmas Liam Stanton, Michael Murillo Electron screening of ions is among the most fundamental properties of plasmas, determining the effective ionic interactions that impact all properties of a plasma. With the development of experimental facilities that probe high energy-density (HED) physics regimes ranging from warm to hot dense matter, an accurate and computationally efficient description of dense plasma screening has become essential. We extend our previous work [Phys. Rev. E, 91, 033104 (2015)], which provides a unified framework for screening models based on finite-temperature orbital-free density functional theory, including both gradient corrections and exchange-correlation effects. Here, we generalize the model to include leading-order core electron effects via the use of pseudo-potentials. We additionally investigate a variety of exchange-correlation models, which are rarely used in simple screening models, and quantify the impact of their contributions across the HED regime with applications such as calculating transport coefficients and equations of state. The results are compared to numerical calculations from high-fidelity physics simulations in the literature. [Preview Abstract] |
Wednesday, October 23, 2019 11:06AM - 11:18AM |
NO7.00009: Systematic \textbf{\textit{ab-initio}}\textbf{ Calculations of Optical Properties of Silicon for Inertial Confinement Fusion Applications} Valentin Karasiev, Suxing Hu Silicon is one of the mid-$Z$ materials used in inertial confinement fusion (ICF) capsules to reduce laser imprint, prevent fuel preheat, and mitigate laser--plasma instability effects. Accurate knowledge of optical properties such as x-ray absorption is crucial for understanding the material response to external electromagnetic radiation and proper ICF target design. In this talk, we will report on systematic calculations of optical properties of silicon in a wide range of material densities and temperatures by means of \textit{first-principles} method based on density functional theory, which take into account quantum effects that are essential in warm-dense-matter regime. Transport properties (thermal and electrical conductivity, dielectric function, index of refraction, reflectivity, absorption, and opacity) of warm dense silicon are calculated within the Kubo--Greenwood formulation with use of the thermal exchange correlation functional and the all-electron projector augmented wave (PAW) data set that is required to provide transferability to extreme conditions of high pressure and temperature. All-electron PAW is also necessary to calculate optical properties in the x-ray range. [Preview Abstract] |
Wednesday, October 23, 2019 11:18AM - 11:30AM |
NO7.00010: Electron-Hole Dynamics during the Formation of Warm Dense Copper Byoung Ick Cho The recent advent of the XFEL allowed us to follow ultrafast electron dynamics in the WDM. We used femtosecond pulses from the PAL-XFEL to measure the ultrafast changes in the X-ray absorption of Cu nanofoil excited by intense laser pulses. Upon exposure to laser irradiation, significant portions of 3d electrons are excited, and the strongly perturbed copper evolves into warm dense matter with temperatures of a few eV. We present the results of measurements of the X-ray absorption spectra below the copper L3 edge with 100 fs resolutions. The data visualize the creation and annihilation of holes in the highly excited 3d band. Comparison of the experiment with the predicted absorption based on the two-temperature-model enabled the initial nonequilibrium durations to be determined at a stage at which the TTM is non-applicable. This investigation allows us to quantify the lifetimes and the decay speed of d holes in warm dense copper. It raises an issue of the fast thermalization concept and the widely used two-temperature model to describe the nascent stage of intensively photoinduced material responses. [Preview Abstract] |
Wednesday, October 23, 2019 11:30AM - 11:42AM |
NO7.00011: How to Relax When You Are Dense and Degenerate: A New Kinetic Theory for Electron-Ion Relaxation Processes in Warm Dense Matter Shane Rightley, Scott Baalrud Temperature and momentum relaxation have proven difficult to compute in systems subject to both strong Coulomb coupling and electron degeneracy. Recent measurements of relaxation under these conditions are providing for the first time an experimental means of validating theoretical and computational methods. We present the application of a mean-force quantum kinetic theory to electron-ion relaxation near equilibrium in a regime where electrons transition between quantum and classical behavior and ions between weak and strong coupling. Using a new closure of the BBGKY hierarchy for the Wigner function, we obtain a kinetic equation in which the collision integral takes the form of the quantum Boltzmann equation of Uehling and Uhlenbeck, but where the binary scattering interactions occur via the equilibrium potential of mean force. The kinetic equation also contains new terms associated with the non-ideal equation of state. Correlations are accounted for to all orders and are computed via established equilibrium methods. We outline the challenges of incorporating degeneracy into mean force kinetic theory and how these are overcome for electron-ion transport. Furthermore, we compare our calculations with recent experimental measurements. Supported by US DOE Grant No. DE-SC0016159. [Preview Abstract] |
Wednesday, October 23, 2019 11:42AM - 11:54AM |
NO7.00012: Electron Transport in Dense Plasmas using the Quantum Landau-F\"okker-Planck Model Nathaniel Shaffer, Charles Starrett We present predictions of electrical and thermal conductivity of dense plas- mas using the quantum Landau-F\"okker-Planck (qLFP) model of collisions. The qLFP model improves on the familiar classical theory because it respects the Pauli Exclusion Principle. This makes it suitable to interrogate the transport properties of hot, dense plasmas, where the electrons are too hot to be treated as a Fermi liquid but too dense to be treated as a classical gas. This important regime is taxing to study with quantum molecular dynamics simulations, and recent evidence suggests that the standard Kubo-Greenwood method for computing thermal conductivity from these simulations lacks essential electron-electron collision effects [M. P. Desjarlais et al., Phys. Rev. E 95, 033203 (2017).]. The qLFP theory is nominally limited to weak-coupling conditions where small-angle scattering dominates transport. We extend its domain of validity to higher densities and lower temperatures using a Coulomb logarithm model that includes strong-coupling effects through a cross-section computed using the potential of mean force. The model recovers the standard Spitzer-H\"arm results in the nondegenerate limit and breaks down in the degenerate liquid-metal regime due to the small-angle approximation. [Preview Abstract] |
Wednesday, October 23, 2019 11:54AM - 12:06PM |
NO7.00013: Efficient Modelling of K-shell Emission for Short-Pulse Laser Experiments in SPECT3D James Sebald, Tim Walton, Igor Golovkin, Joseph MacFarlane Cold K-alpha and K-beta emission provides a diagnostic for hot electron distributions produced in short pulse laser experiments. Spect3D is able to post-process results of PIC simulations and compute high-resolution spectra for plasmas containing arbitrary distributions of hot electrons. These calculations, however, require comprehensive sets of atomic data and can become prohibitively expensive for modest and large simulation grids. To significantly increase calculation speed, it is desirable to use pre-computed emissivity/opacity tables that include effects of hot electrons, rather than calculating the data for every spatial zone. However, to tabulate results for arbitrary hot electron energy distributions, a general method must be found to describe arbitrary energy distributions with an analytic function of just a few parameters. We will present a set of PrismSPECT and Spect3D results validating the replacement of hot electron distributions with a Gaussian function determined by each hot electron distribution. Tests are performed on LSP simulations for experiments on Omega EP. [Preview Abstract] |
Wednesday, October 23, 2019 12:06PM - 12:18PM |
NO7.00014: Quantum hydrodynamics for plasmas--quo vadis? Michael Bonitz, Hanno Kählert, Zhandos Moldabekov, Tlekkabul Ramazanov Quantum hydrodynamics (QHD) has become popular for modeling of quantum plasmas and warm dense matter, following Ref. 1. While QHD is quite successful for describing Bose-Einstein condensates and plasmonic excitations in metallic nanoparticles, the application of the model of Ref. [1] to dense plasmas has lead to oversimplified fluid equations. These equations neiter reproduce the correct plasmon dispersion (except for 1D models) nor the screened potential of an ion in a quantum degenerate plasma [2, 3] and have led to astonishing predictions that have been controversially discussed. Here we present a systematic derivation, starting from quantum statistical theory, that leads to microscopic QHD equations that are in agreement with time-dependent DFT and quantum kinetic theory and which serve as a basis for deriving improved QHD models for plasmas [3].\\ $[1]$ G. Manfredi and F. Haas, Phys. Rev. B 74, 075316 (2001)\\ $[2]$ Zh. Moldabekov, M. Bonitz, and T. Ramazanov, Phys. Plasmas 25, 031903 (2018)\\ $[3]$ M. Bonitz, Zh. Moldabekov, and T. Ramazanov, Phys. Plasmas (2019) [Preview Abstract] |
Wednesday, October 23, 2019 12:18PM - 12:30PM |
NO7.00015: First principles investigation of the insulator-metal transition in liquid hydrogen with a recently developed deorbitalized meta-GGA exchange-correlation functional Joshua Hinz, Valentin Karasiev, Suxing Hu, Mahamed Zaghoo, Daniel Mejia-Rodriguez Through calculations of optical and structural properties from ab initio quantum molecular dynamic simulations we have determined the insulator- metal transition (IMT) boundary for hydrogen and deuterium using the deorbitalized meta-GGA exchange correlation functional SCAN-L with the nonlocal correlation correction rVV10. The two separate criteria of a dc conductivity of 2000 S/cm and the energy gap closure from the density of states provide a consistent IMT boundary that is in good agreement with recent static compression experiments. Furthermore, upon inclusion of nuclear quantum effects via path integral molecular dynamics our initial IMT boundary shifts toward lower pressures providing an excellent agreement with three separate experiments and indicates a clear step like feature, with a physics discussion here within, consistent with coupled electron-ion Monte Carlo predictions. [Preview Abstract] |
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