Bulletin of the American Physical Society
56th Annual Meeting of the APS Division of Plasma Physics
Volume 59, Number 15
Monday–Friday, October 27–31, 2014; New Orleans, Louisiana
Session GI2: Fundamental High Energy Density Physics |
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Chair: Carolyn Kuranz, University of Michigan Room: Bissonet |
Tuesday, October 28, 2014 9:30AM - 10:00AM |
GI2.00001: Scaling a High-Energy-Density Shear Experiment from Omega to the National Ignition Facility (NIF) Invited Speaker: Forrest W. Doss Shear instability in high-energy-density (HED) physics is important for elucidating issues in compressible turbulence and in understanding the late time quenching of, for example, inertial fusion capsules. A counterflowing shear experiment initially designed for the Omega Laser Facility studies shear instability in isolation by launching 100+~km/s shocks into opposite sides of a foam-filled shock tube bisected by an Al tracer plate. When the shocks cross at the tube center, a region of intense shear is created ($\sim150$~km/s velocity difference from one side of the plate to the other). As the tracer layer goes unstable it mixes with the surrounding foam and expands into the tube volume. Radiography recording the spreading of the mixing layer is compared to simulations using the LANL hydrocode RAGE. Analysis of this data demonstrated the likely presence of features, such as strong coupling between the thermodynamics and turbulence during the experiment, of special or unique importance to the HED regime. However, the Omega experiments are limited to 1~ns impulsive drive, compared to the 16~ns of observation times, and are dominated by transients, barely if at all reaching the state of developed turbulence. Our recent shots on the NIF take the experiment to larger volumes, to faster speeds, and to the use of indirect drive halfraums to launch steadily supported shocks. These improvements take advantage of the increased energy of the NIF to eliminate transients and drive more steadily the approach to turbulent transition. Analysis of radiographs confirms our ability to model the hydrodynamic drive and evolution, while comparing images of the developing turbulence between the two facilities suggests morphological differences related possibly to the change in drive conditions. This work was supported by the US DOE and operated by LANS under Contract No. DE-AC52-06NA25396. [Preview Abstract] |
Tuesday, October 28, 2014 10:00AM - 10:30AM |
GI2.00002: Relativistic electron-positron jets and plasmas using intense lasers Invited Speaker: Hui Chen High-flux jets of electron-positron antimatter with temperatures of a few trillion degrees have been produced in experiments at high-intensity laser facilities [1-5]. These breakthrough experiments open up a novel area of experimental high-energy-density plasma astrophysics identified in several recent national reports. These experiments are on a path toward the production of relativistic electron-positron ``pair'' plasmas [2], allowing for interactive study of a state of matter otherwise found only in exotic astrophysical systems such as active galaxies, quasars, gamma ray bursts, black holes, and conditions existing shortly after the Big Bang. This presentation describes the physical processes for making pairs and summarizes recent results from several large intense laser facilities [2, 3]. These results include the pair jet energy, angular divergence and emittance [4]; the pair jet temperature and density; pair production scalings [6] and collimation by external magnetic fields [5]; and sensitivity to laser intensity (10$^{18}$ - 10$^{21}$ Watts/cm$^2$), contrast (10$^7$ - 10$^{10}$), and energy (100 - 2000 J). The presentation concludes with discussion of possibilities to exploit laser-produced pair jets and plasmas. \\[4pt] This work was performed under the auspices of the U.S. DOE by LLNL under Contract DE-AC52-07NA27344. \\[4pt] [1] H. Chen, S. C. Wilks, J. D. Bonlie, \textit{et al.}, Phys. Rev. Lett. \textbf{102}, 105001 (2009)\\[0pt] [2] H. Chen, S. C. Wilks, D. D. Meyerhofer, \textit{et al.}, Phys. Rev. Lett. \textbf{105}, 015003 (2010) \\[0pt] [3] H. Chen, M. Nakai, Y. Sentoku, \textit{et al.}, New J. Phys. \textbf{15,} 065010 (2013)\\[0pt] [4] H. Chen, J. C. Sheppard, D. D. Meyerhofer, \textit{et al.}, Phys. Plasmas \textbf{20}, 012507 (2013)\\[0pt] [5] H. Chen, G. Fiksel, D. Barnak, \textit{et al.}, Phys. Plasmas (Letter) \textbf{21}, 040703 (2014)\\[0pt] [6] H. Chen, F. Fiuza, A. Link, Y. Sentoku, \textit{et al.}, submitted (2014) [Preview Abstract] |
Tuesday, October 28, 2014 10:30AM - 11:00AM |
GI2.00003: Dynamic compression experiments on liquid deuterium above the melt boundary to investigate the insulator-to-metal transition Invited Speaker: Marcus Knudson Recently we have been exploring various pulsed power experimental concepts to access off-Hugoniot states in liquids at the Sandia Z Accelerator. One very promising technique utilizes a so-called shock-ramp platform. Here a relatively small gap is introduced between the ramp compression load electrode and a liquid sample cell. The accelerator is configured to deliver a two-step current pulse; the first step accelerates the electrode to a reasonably constant velocity, which upon impact with the sample cell creates a well-defined shock, while the subsequent current rise produces ramp compression from the initially shocked state. This technique makes it possible to achieve relatively cool ($\sim$ 1000-2000 K), high pressure (\textgreater 300 GPa), high compression states ($\sim$ 10-15 fold compression), allowing experimental access to the region of phase space where hydrogen is predicted to undergo a first-order phase transition from an insulating molecular-like liquid to a conducting atomic-like fluid. In this talk we will discuss the development of the liquid shock-ramp platform, survey the various theoretical predictions for the liquid-liquid transition in hydrogen, and present the results of initial experiments performed that access this region of phase space. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. [Preview Abstract] |
Tuesday, October 28, 2014 11:00AM - 11:30AM |
GI2.00004: Observation of Self-Similarity in the Magnetic Fields Generated by the Ablative Nonlinear Rayleigh-Taylor Instability Invited Speaker: Lan Gao The Rayleigh-Taylor (RT) instability has been extensively studied because of its relevance to ignition target designs in inertial confinement fusion, material strength studies in high energy density physics, and astrophysical systems. This talk presents the first measurements of magnetic field generation by the nonlinear RT instability in laser-accelerated planar foils using ultrafast proton radiography at the OMEGA EP Laser System. Thin plastic foils were irradiated with 4-kJ, 2.5-ns laser pulses at focused laser intensities of $\sim$10$^{14}$ W$/$cm$^{2}$. Target modulations were seeded by laser nonuniformities and amplified during the target-acceleration phase by the RT instability growth. A high-energy proton beam tracked the hydrodynamic evolution of the target and mapped the magnetic field spatial distribution with high spatial and temporal resolution. The experimental data show self-similar behavior [1] in the growing cellular magnetic field structures [2-3]. The calculated magnetic cell-merging rate is consistent with the value determined by earlier x-ray measurements [4], linking the cellular magnetic field structures with the RT bubble and spike growth. The results are consistent with two-dimensional magnetohydrodynamic simulations, showing MG-level magnetic field generation in the laser-driven foil [3]. The work could benefit the understanding of magnetic-seed-field generation in high energy density plasmas and the flow-driven processes that induce global magnetic structures prior to their turbulent amplification by the dynamo process. \\[4pt] [1] U. Alon et al., Phys. Rev. Lett. 72, 2867 (1994).\\[0pt] [2] L. Gao et al., Phys. Rev. Lett. 110, 185003 (2013).\\[0pt] [3] L. Gao et al., Phys. Rev. Lett. 109, 115001 (2012).\\[0pt] [4] O. Sadot et al., Phys. Rev. Lett. 95, 265001 (2005); V. A. Smalyuk et al., Phys. Rev. Lett. 81, 5342 (1998) [Preview Abstract] |
Tuesday, October 28, 2014 11:30AM - 12:00PM |
GI2.00005: Experimental Measurements and Density Functional Theory Calculations of Continuum Lowering in Strongly Coupled Plasmas Invited Speaker: Sam Vinko An accurate description of the ionization potential depression (IPD) of ions in plasmas due to their interaction with the environment is a fundamental problem in plasma physics, playing a key role in determining the ionization balance, charge state distribution, opacity and plasma equation of state. Here I present the first experimental investigation of the IPD as a function of ionic charge state in a range of dense Mg, Al and Si plasmas, using the Linac Coherent Light Source X-ray free-electron laser. The measurements show significantly larger IPDs than are predicted by the most commonly used models, such as that of Stewart-Pyatt, or the ion-sphere model of Zimmerman-More. Instead, plasma simulations using finite-temperature density functional theory with excited-state projector augmented-wave potentials show excellent agreement with the experimental results and explain the stronger-than-expected continuum lowering through the electronic structure of the valence states in these strong-coupling conditions, which retain much of their atomic characteristics close to the ion core regions. These results have a profound impact on the understanding and modelling of plasmas over a wide range of warm- and hot-dense matter conditions. \\[4pt] [1] S.M. Vinko {\it et al.}, Nature {\bf 482}, 59 (2012).\\[0pt] [2] O. Ciricosta {\it et al.}, PRL {\bf 109}, 065002 (2012).\\[0pt] [3] S.M. Vinko {\it et al.}, Nat. Comm. {\bf 5}, 3553 (2014).\\[0pt] [4] J.C. Stewart and K.D. Pyatt, Astrophys. J. {\bf 144}, 1203-1211 (1966).\\[0pt] [5] G.B. Zimmerman and R.M. More, J. Quant. Spectrosc. Radiat. Transfer {\bf 23}, 517-522 (1980). [Preview Abstract] |
Tuesday, October 28, 2014 12:00PM - 12:30PM |
GI2.00006: Free-electron laser measurements of plasmons in warm dense matter Invited Speaker: Eliseo Gamboa Strong plasmon resonances characteristic of electron density fluctuations in warm dense matter (WDM) plasmas have recently been observed for the first time at the Linac Coherent Light Source (LCLS). These experiments record forward scattering from ultrabright 8 keV x-ray pulses to probe dynamically compressed solids driven by shaped ns laser pulses at the Matter in Extreme Conditions (MEC) instrument. From the x-ray scattering spectra we observe well-pronounced plasmon peaks that directly access the electron densities and temperatures. We can access densities \textgreater 5 g/cm$^{\mathrm{3}}$ and pressures approaching 5 Mbar that are important for planetary and material science as well as inertial confinement fusion research. In this talk we characterize the plasmon loss against wavenumber-resolved x-ray scattering that provides an independent density measurement through shifted Bragg and ion-ion correlation scattering features. We will compare ideal plasma states achieved in heated aluminum with those measured from uncompressed and compressed CVD diamond. The latter shows plasmon energies strongly affected by the band structure up to the highest experimental pressures of several Mbar. This method is presently being applied in numerous experiments to characterize the physical properties of dense plasmas. We will describe the first demonstration of this technique at LCLS, present applications to characterize shocks in dense plasmas, and discuss novel ideas for measuring the properties of high-pressure materials. [Preview Abstract] |
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