Bulletin of the American Physical Society
58th Annual Meeting of the APS Division of Plasma Physics
Volume 61, Number 18
Monday–Friday, October 31–November 4 2016; San Jose, California
Session TI2: HEDP: Warm Dense Matter, Equation of State and Plasma EffectsInvited
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Chair: Siegfried Glenzer, Stanford University Room: 210 CDGH |
Thursday, November 3, 2016 9:30AM - 10:00AM |
TI2.00001: Building a laboratory foundation for interpreting spectral emission from x-ray binary and black hole accretion disks. Invited Speaker: Guillaume Loisel Emission from accretion powered objects accounts for a large fraction of all photons in the universe and is a powerful diagnostic for their behavior and structure. Quantitative interpretation of spectrum emission from these objects requires a spectral synthesis model for photoionized plasma, since the ionizing luminosity is so large that photon driven atomic processes dominate over collisions. This is a quandary because laboratory experiments capable of testing the spectral emission models are non-existent. The models must predict the photoionized charge state distribution, the photon emission processes, and the radiation transport influence on the observed emission. We have used a decade of research at the Z facility to achieve the first simultaneous measurements of emission and absorption from photoionized plasmas. The extraordinary spectra are reproducible to within $+$/- 2{\%} and the E/dE \textasciitilde 2500 spectral resolution has enabled unprecedented tests of atomic structure calculations. The absorption spectra enable determination of plasma density, temperature, and charge state distribution. The emission spectra then enable tests of spectral emission models. The emission has been measured from plasmas with varying size to elucidate the radiation transport effects. This combination of measurements will provide strong constraints on models used in astrophysics. Sandia is a multi-program laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under contract DE-AC04-94AL85000. [Preview Abstract] |
Thursday, November 3, 2016 10:00AM - 10:30AM |
TI2.00002: Generation and Characterization of States of Matter at Solar Core Conditions Invited Speaker: Benjamin Bachmann The equation-of-state (EOS) of matter at solar core conditions is important to stellar evolution models and understanding the origin of high Z elements. Temperatures, densities and pressures of stellar cores are, however, orders of magnitude greater than those obtained in state-of-the-art laboratory EOS experiments [1] and therefore such conditions have been limited to observational astronomy and theoretical models. Here we present a method to generate and diagnose these conditions in the laboratory, which is the first step towards characterizing the EOS of such extreme states of matter. By launching a converging shock wave into a deuterated plastic sphere ($CD_{2}$) we produce solar core conditions ($R/R_{Sun}<0.2$) which are initiated when the shock reaches the center of the $CD_{2}$ sphere and extends during transit of the reflected wave until the temperature drops to a level where the neutron production and x-ray self emission drop below threshold levels of the detectors. These conditions are diagnosed by both, the neutron spectral data from D-D nuclear reactions, and temporal, spatial [2,3], and spectral [4] x-ray emission data. We will discuss how these observables can be measured and used to help our understanding of dense plasma states that reach well into the thermonuclear regime of stellar cores. \newline \newline [1] R. F. Smith \textit{et al.}, Ramp compression of diamond to five terapascals, Nature 511, 330-333 (2014) \newline [2] B. Bachmann \textit{et al.}, Using penumbral imaging to measure micrometer size plasma hot spots in Gbar equation of state experiments, Rev. Sci. Instrum. 85, 11D606 (2014) \newline [3] B. Bachmann \textit{et al.}, Resolving hot spot microstructure using x-ray penumbral imaging (invited), Rev. Sci. Instrum. 87, accepted for publication (2016) \newline [4] B. Bachmann \textit{et al.}, High-speed three-dimensional plasma temperature determination of axially symmetric free-burning arcs, J. Phys. D: Appl. Phys. 46, 125203 (2013) [Preview Abstract] |
Thursday, November 3, 2016 10:30AM - 11:00AM |
TI2.00003: The Shock and Release Behavior of Diamond Compressed to 25 Mbar Invited Speaker: M.C. Gregor The behavior of carbon at high pressure is important to the study of ice giants and white dwarfs, and because diamond is used as an ablator for inertial confinement fusion (ICF) targets at the National Ignition Facility (NIF). The adiabat of an ICF implosion is determined by a series of shocks that transit the ablator and fuel layer. To accurately model an implosion and design ignition targets, both the Hugoniot and the release behavior of the ablator material must be known. We report on experiments on the OMEGA laser that shocked diamond samples up to 25 Mbar, which then released into reference materials with known Hugoniots (quartz, 200-mg/cm$^{\mathrm{3}}$ SiO$_{\mathrm{2}}$ foam, liquid deuterium, and polystyrene). The impedance-matching technique with these reference materials provided data that constrains release models for diamond. This technique is applied to two forms of diamond: single-crystal and ultra-nanocrystalline diamond (UNCD); the latter is the NIF ablator material. Models for the release isentropes of both types of diamond will be developed using a Mie--Gr\"{u}neisen equation of state. This study also provided Hugoniot data for UNCD using the impedance-matching technique with a quartz standard. The accuracy of these data was improved by implementing an unsteady wave correction\footnote{D. E. Fratanduono \textit{et al}., J. Appl. Phys. \textbf{116}, 033517 (2014).\par } to determine instantaneous shock velocities in the opaque UNCD samples. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. [Preview Abstract] |
Thursday, November 3, 2016 11:00AM - 11:30AM |
TI2.00004: Ab initio thermodynamic results for warm dense matter Invited Speaker: Michael Bonitz Warm dense matter (WDM) -- an exotic state where electrons are quantum degenerate and ions may be strongly correlated -- is ubiquitous in dense astrophysical plasmas and highly compressed laboratory systems including inertial fusion. Accurate theoretical predictions require precision thermodynamic data for the electron gas at high density and finite temperature around the Fermi temperature. First such data have been obtained by restricted path integral Monte Carlo (restricted PIMC) simulations [1] and transformed into analytical fits for the free energy [2]. Such results are also key input for novel finite temperature density functional theory.\\ \\However, the RPIMC data of Ref. 1 are limited to moderate densities, and even there turned out to be surprisingly inaccurate, which is a consequence of the fermion sign problem. These problems were recently overcome by the development of alternative QMC approaches in Kiel (configuration PIMC [3, 4] and permutation blocking PIMC [5]) and Imperial College (Density matrix QMC [5]). The three methods have their strengths and limitations in complementary parameter regions and provide highly accurate thermodynamic data for the electronic contributions in WDM. While the original results [4-7] were obtained for small particle numbers, recently accurate finite size corrections were derived allowing to compute ab initio thermodynamic data with an unprecedented accuracy of better than 0.3 percent. This provides the final step for the use as benchmark data for experiments and models of Warm dense matter.\\ \\$[1]$ E.W. Brown et al., Phys. Rev. Lett. \textbf{110}, 146405 (2013). [2] V.V. Karasiev et al., Phys. Rev. Lett. \textbf{112}, 076403 (2014). [3] T. Schoof et al., Contrib. Plasma Phys. \textbf{51}, 687 (2011). [4] T. Schoof et al. Phys. Rev. Lett. \textbf{115}, 130402 (2015) [5] T. Dornheim et al., J. Chem. Phys. \textbf{143}, 204101 (2015). [6] F.D. Malone et al., J. Chem. Phys. \textbf{143}, 044116 (2015). [7] S. Groth, T. Dornheim, et al., Phys. Rev. B \textbf{93}, 085102 and 205134 (2016). [Preview Abstract] |
Thursday, November 3, 2016 11:30AM - 12:00PM |
TI2.00005: Ultrafast visualization of the structural evolution of dense hydrogen towards warm dense matter Invited Speaker: Luke Fletcher Hot dense hydrogen far from equilibrium is ubiquitous in nature occurring during some of the most violent and least understood events in our universe such as during star formation, supernova explosions, and the creation of cosmic rays. It is also a state of matter important for applications in inertial confinement fusion research and in laser particle acceleration. Rapid progress occurred in recent years characterizing the high-pressure structural properties of dense hydrogen under static or dynamic compression. Here, we show that spectrally and angularly resolved x-ray scattering measure the thermodynamic properties of dense hydrogen and resolve the ultrafast evolution and relaxation towards thermodynamic equilibrium. These studies apply ultra-bright x-ray pulses from the Linac Coherent Light (LCLS) source. The interaction of rapidly heated cryogenic hydrogen with a high-peak power optical laser is visualized with intense LCLS x-ray pulses in a high-repetition rate pump-probe setting. We demonstrate that electron-ion coupling is affected by the small number of particles in the Debye screening cloud resulting in much slower ion temperature equilibration than predicted by standard theory. [Preview Abstract] |
Thursday, November 3, 2016 12:00PM - 12:30PM |
TI2.00006: Observation of Interspecies Ion Separation in Inertial-Confinement-Fusion Implosions via Imaging X-ray spectroscopy Invited Speaker: Tirtha Raj Joshi Interspecies ion separation has been proposed as a yield-degradation mechanism in inertial-confinement-fusion (ICF) experiments. We present direct experimental evidence of interspecies ion separation in direct-drive ICF experiments performed at the OMEGA laser facility. These experiments were designed based on the fact that interspecies ion thermo-diffusion [1]$^{\mathrm{\thinspace }}$would be strongest for species with large mass and charge difference. The targets were spherical plastic shells filled with D$_{\mathrm{2}}$ and Ar (1{\%} by atom). Ar K-shell spectral features were observed primarily between the time of first-shock convergence and slightly before neutron bang time, using a time- and space-integrated spectrometer, streaked crystal spectrometer, and two gated multi-monochromatic X-ray imagers fielded along quasi-orthogonal lines-of-sight. Detailed spectroscopic analyses of spatially resolved Ar K-shell lines reveal deviation from the initial 1{\%}-Ar gas fill and show both Ar-concentration enhancement and depletion at different times and radial positions of the implosion. The experimental results are interpreted with radiation-hydrodynamic simulations that include recently implemented, first-principles models [2] of interspecies ion diffusion. The experimentally inferred Ar-atom-fraction profiles agree gently with calculated profiles associated with the incoming and rebounding first shock. This work was done in collaboration with P. Hakel, S. C. Hsu, E. L. Vold, M. J. Schmitt, N. M. Hoffman, R. M. Rauenzahn, G. Kagan, X.-Z. Tang, Y. Kim, and H. W. Herrmann of LANL, and R. C. Mancini of UNR. LA-UR-16-24804. [Preview Abstract] |
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