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 PI2: Invited: Weimer Award, High Energy Density Science |
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Chair: Stephanie Hansen, Sandia National Lab Room: Floridian Ballroom AB |
Wednesday, October 23, 2019 2:00PM - 2:30PM |
PI2.00001: Katherine E. Weimer Award Talk: Studying 3D asymmetries and resulting flows in ICF implosions, and using ICF implosions to study nuclear reactions relevant to stellar nucleosynthesis Invited Speaker: Maria Gatu Johnson This broad talk will cover two topics. Firstly, low-mode asymmetries have emerged as one of the primary challenges to achieving high-performing inertial confinement fusion (ICF) implosions. These asymmetries seed flows in the implosions, which manifest as modifications to the measured ion temperature (Tion) and as directional flow inferred from the broadening and energy shift of primary neutron spectra. The effects are important to understand both to learn to control and mitigate low-mode asymmetries, and to more closely capture thermal Tion used as input in implosion performance metric calculations. We report on intentionally asymmetrically driven OMEGA implosions, which demonstrate the importance of interplay of flows induced by various asymmetry seeds. Tion, peak shift, areal-density asymmetry and x-ray imaging measurements are brought to bear and contrasted to CHIMERA, xRAGE, ASTER and DRACO simulations, providing insights into implosion dynamics and the interplay between different asymmetry sources, including laser drive non-uniformity, the stalk, and capsule offset. Secondly, thermonuclear reaction rates and nuclear processes have been explored traditionally by means of accelerator experiments, which are difficult to execute at conditions relevant to Stellar Nucleosynthesis. ICF plasmas closely mimic astrophysical environments and are an excellent complement to accelerator experiments. We describe ICF experiments to study the T$+$T reaction at the OMEGA laser facility, and the mirror solar 3He$+$3He reaction at the National Ignition Facility (NIF), as well as discuss future directions for exploring light-ion reactions at OMEGA and the NIF. In particular, we show how measurements of the T$+$T reaction at OMEGA at Tion from 4 to 18 keV provide the first conclusive evidence of a variant T$+$T-neutron spectrum over the corresponding center-of-mass energy range (16-50 keV). [Preview Abstract] |
Wednesday, October 23, 2019 2:30PM - 3:00PM |
PI2.00002: Recent Advancements on Opacity-on-NIF at Anchor 1: 160eV, 7e21/cm3 Invited Speaker: Heather Johns The Opacity-on-NIF campaign is a 5-lab collaboration, complementary to the Opacity-on-Z effort, that works to provide opacity data for Fe and other elements for comparison to theory [1]. The goal is to address the discrepancy between theory and the Opacity-on-Z experiments for temperatures between Te = 170-200eV, Ne = 2-4e22/cm3 [2]. For 160eV and 7e21/cm3 and below, where Opacity-on-Z and theory had better agreement, the first iron transmission data for Opacity-on-NIF has been published [3]. In that context, we will overview the current state of the platform for these conditions, including simulations [4], target fabrication modifications [5], spectrometer updates, and other recent advances needed to reduce platform uncertainties to approach the tight constraints on conditions required for an Opacity measurement on NIF. We will pay additional attention to plasma density determination, providing a comparison between density obtained from imaging the expanding sample through an aperture in the hohlraum wall [3,4,5], and density obtained from Stark broadening analysis of Mg lines, such as was done for Opacity-on-Z [6] using Stark-broadened lineshapes generated by MERL [7]. We will also discuss the plasma temperature determination. 1. T. S. Perry, R. Heeter, F. Opachich et al, HEDP 23, 223-227 (2017) 2. J.E. Bailey, T. Nagayama, G. P. Loisel et al., Nature 517 56-67, (2015) 3. R. F. Heeter, T. Perry, H. Johns, et al Atoms 6, 57, (2018) 4. E.S. Dodd, B. G. DeVolder, M.E. Martin et al, POP 25, 063301 (2018) 5. T. Cardenas, D.W. Schmidt, E. S. Dodd et al, Fusion Sci. Technol. 73, 458 (2018) 6. J. E. Bailey, G. A. Rochau, R. C. Mancini et al, RSI 79, 113104 (2008). 7. R. C. Mancini, D. P. Kilcrease, L. A. Woltz, et al, Computer Physics Communications 63, 314 (1991). [Preview Abstract] |
Wednesday, October 23, 2019 3:00PM - 3:30PM |
PI2.00003: Direct Electron Acceleration in Multi-Kilojoule, Multi-Picosecond Laser Pulses Invited Speaker: Andreas Kemp The physics mechanism behind the acceleration of electrons to energies much higher than the laser ponderomotive potential is reported on. Such electrons have been observed for the last twenty years [Perry], but they were small in number, about 1 percent of MeV electrons. Extended pulse durations, large focal spots and high intensities of current high-power lasers all favor generation of `super-ponderomotive' electrons. Recent PIC simulations [Sorokovikova] give twenty times larger MeV electron doses than NOVA-PW. Such an enhancement, if realized in experiments, would boost all applications of short laser pulses (e.g., proton/ion acceleration, X-ray generation, and positron production). Evidence is provided that the dominant acceleration mechanism of super-pondermotive electrons is direct acceleration by transverse electromagnetic fields as they co-propagate in under-dense plasma; the most energetic electrons are initially Raman-scattered in the opposite direction of the laser pulse and then reflected by the electrostatic potential at the front of the plasma expansion into vacuum. In the classical figure-of-eight motion in a plane wave, electrons gain only a small average forward drift with momentum proportional to a$_{\mathrm{0}}^{\mathrm{2}}$/2 while oscillating in the laser field; in contrast, electrons injected at relativistic energy remain in phase with the laser field longer gain several times more energy, running in- and out of phase with the light; this continues until the laser is reflected by over-critical plasma, while fast electrons propagate into the target. Direct acceleration requires tens of plasma wavelengths of under-dense plasma, as well as pulse durations of tens of plasma periods, conditions that are found in large focal spot multi-picosecond laser pulses. References: Sorokovikova, A., Arefiev et al., Phys.Rev.Lett. 116, 155001 (2016). Perry, et al., Rev.Sci. Instr. 70, 265 (1999). [Preview Abstract] |
Wednesday, October 23, 2019 3:30PM - 4:00PM |
PI2.00004: Towards \textit{ab initio}simulation of 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 astrophysics and highly compressed laboratory plasmas. We have recently obtained \textit{ab initio}thermodynamic results for the electron component in WDM based on novel quantum Monte Carlo (QMC) simulations [1-3] including the first \textit{ab initio}parametrization of the exchange-correlation free energy F\textunderscore xc [3, 4], and here we present applications using finite temperature DFT simulations. In addition, also inhomogeneous systems have been studied giving rise to \textit{ab initio}results for the static structure factor. Moreover, recently the first exact QMC result for the dynamic structure factor could be obtained [5]. An interesting result is the prediction of a negative plasmon dispersion in the range of strong electronic correlations -- an effect that should be observable in dense hydrogen. Finally, an outlook is presented on how to accurately treat degenerate electrons in WDM out of equilibrium. Here we discuss two approaches: quantum hydrodynamics for which a microscopic derivation is given [6]. The second is nonequilibrium Green functions which allow for a rigorous extension of kinetic equations to ultrafast relaxation processes [7]. [1] T. Schoof, S. Groth, J. Vorberger, and M. Bonitz, Phys. Rev. Lett. , 130402 (2015) [2] T. Dornheim, S. Groth, T. Sjostrom, F.D. Malone, W.M.C. Foulkes, and M. Bonitz, \underline {Phys. Rev. Lett. , 156403 (2016)} [3]S. Groth, T. Dornheim, T. Sjostrom, F.D. Malone, W.M.C. Foulkes, and M. Bonitz, \underline {Phys. Rev. Lett. , 135001 (2017)} [4] T. Dornheim, S. Groth, and M. Bonitz, Phys. Reports , 1-86 (2018) [5] T. Dornheim, S. Groth, J. Vorberger, and M. Bonitz, Phys. Rev. Lett. , 255001 (2018) [6] M. Bonitz, Zh. Moldabekov, and T. Ramazanov, Phys. Plasmas, submitted [7] M. Bonitz, ``Quantum Kinetic Theory'', 2$^{\mathrm{nd}}$ed., Springer 2016 [Preview Abstract] |
Wednesday, October 23, 2019 4:00PM - 4:30PM |
PI2.00005: First-Principles Determination of Electron-Ion Energy Relaxation Rates in the Warm Dense Matter Regime Invited Speaker: Jacopo Simoni The last decade has seen remarkable progress in our ability to create in the laboratory materials in the warm dense matter regime. These advances require improved understanding and forward modeling of the non-equilibrium conditions typically created in these experiments. In particular, much uncertainty remains in our predictive capability of the electron-ion energy relaxation timescales as illustrated by the strong disagreements among analytical models and with measurements. In this work [1] we present the first ab-initio calculations of the electron-ion energy relaxation rates in warm dense plasmas, liquid metals, and hot solids. To this end, we first derive a general expression for the rate and evaluate it numerically from quantum molecular dynamics simulations. Our theory includes self-consistently the various quantum, thermal, non-linear and strong coupling effects that coexist in warm dense plasmas, and it reduces to well-known models in limiting cases. We discuss results obtained for several representative materials, including H, Al, Cu, Ni and Fe, over a wide range of conditions. Our approach serves as a very useful comparison with experimental measurements and models, permits an extension into conditions not covered by experiments, and provides insight into the underlying physics. [1] J. Simoni and J. Daligault, First-Principles Determination of Electron-Ion Couplings in the Warm Dense Matter Regime, Phys. Rev. Lett. 122, 205001 (2019). [Preview Abstract] |
Wednesday, October 23, 2019 4:30PM - 5:00PM |
PI2.00006: Three-dimensional metal deformation and plasma formation driven by resistive inclusions Invited Speaker: Edmund Yu Understanding how electrical current flows through conductors is essential to a wide variety of applications, from magneto-inertial fusion to protoplanetary disk heating. The problem is complicated by the dependence of electrical conductivity $\sigma$ on temperature, resulting in the Ohmic heating-driven electrothermal instability (ETI). Assuming current J flows vertically, ETI forms horizontal, hot striations in metals, and vertical filaments in plasmas. Striations seed the magneto Rayleigh-Taylor instability, which shreds apart metal in applications involving acceleration; filaments drive plasma formation, important in the design of next-generation pulsed power drivers. However, ETI theory does not address what seeds the striations/filaments, nor how horizontal striations transition into vertical filaments. In this work, we model current flow through a metal rod, using 3D MHD simulation, and show how J redistribution around a resistive inclusion can seed both striations and filaments. Initially, J amplifies around the inclusion's equator, driving enhanced Ohmic heating, which alters $\sigma(r)$, thus further modifying J. This feedback loop grows the inclusion transverse to J, forming a striation. The overheated striation later explodes, but due to J redistribution, the expanding plume develops asymmetrically, expanding vertically but focusing horizontally, thus forming the filament predicted by ETI. Hence, ETI-assisted plasma formation is a fully 3D process, occurring earlier and at 10X higher density than predicted by 1D simulation. [Preview Abstract] |
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