Bulletin of the American Physical Society
59th Annual Meeting of the APS Division of Plasma Physics
Volume 62, Number 12
Monday–Friday, October 23–27, 2017; Milwaukee, Wisconsin
Session CI3: HED |
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Chair: Bhuvana Srinivasan, Virginia Tech Room: 103ABC |
Monday, October 23, 2017 2:00PM - 2:30PM |
CI3.00001: Late-time mixing and turbulent behavior in high-energy-density shear experiments at high Atwood numbers Invited Speaker: Kirk Flippo The LANL Shear experiments on the NIF are designed to study the Kelvin-Helmholtz instability (KHI), which is the predominate mechanism for generating vorticity, leading to turbulence and mixing at high Reynolds numbers. The KHI is pervasive, as velocity sheared and density-stratified flows abound, from accretion disks of a black holes to the fuel capsule in an ICF implosion. The NIF laser has opened up a new class of long-lived planar HED fluid instability experiments that can scale fluid experiments over impressive orders of magnitude in pressure ( up to $>$ Mbar), temperature ( $>$ 10$^{5}$ K) and space ($<$ 10s of $\mu$m) and still recover classical fluid instability behavior, and elucidate mixing and plasma effects. The reproducibility allows for the unique capability in an HED experiment to directly measure values comparable to those in the mix model, the Besnard-Harlow-Rauenzahn (BHR[3]) model implemented in the LANL hydro-code RAGE, like the mixedness parameter, $b$, and the turbulent kinetic energy using the observed coherent features. We have acquired time histories of 4 tracer materials and 3 surface finishes spanning dynamic Atwood numbers from 0.63 to 0.88 and developed Reynolds numbers around 10$^{6}$. When the shocks cross, the layer is exposed to extreme shear forces and evolves into KHI rollers from an unseeded (but naturally broadband) surface. Two sets of data are acquired for each material type: an edge-view and a plan-view, through the plane of the material. The results hint at plasma physics effects in the layer. The edge-view is compared to BHR calculations, to understand mixing and layer growth. The BHR model matches the evolution and asymptotic behavior of the layer, and the initial scale-length used for the model correlates well to initial surface roughness, even when the surface is artificially roughened, forcing the layer’s evolution from coherent to disordered. [Preview Abstract] |
Monday, October 23, 2017 2:30PM - 3:00PM |
CI3.00002: Development of High Fluence, High Conversion Efficiency X-Ray Sources at the National Ignition Facility Invited Speaker: Mark May Laser heated millimeter scale targets have provided recently some of the most powerful and energetic laboratory sources of x-ray photons (E = 6 - 24 keV) with high fluence and conversion efficiency (CE). These sources have included the K-shell of stainless steel (E = 5-9 keV) from cylindrical cavities having a CE of $\sim$ 6.8 % (E$_{tot}$ $\sim$ 31 kJ), the K-shell of Kr (E = 8-20 keV) from gas pipes having a CE of $\sim$ 1.6% ($\sim$ 20 kJ) and the L-shell of Ag (E = 3-5 keV) from novel nano-wire foam targets having a CE of $\sim$ 16% ($\sim$ 81 kJ). The x-ray power and CE are dependent upon the peak electron temperature in the radiating plasma created from these underdense (n$_{e}$ $<$ 0.25 n$_{c}$) sources. The temperature can be limited by the available laser power and energy which can cause the fluence and the CE to be suboptimal especially for high Z K-shell sources. Cavity targets require several nanoseconds for the underdense plasma to fill the cavity but do have an increase in temperature and emission at late time from plasma stagnation on axis. In contrast the gas or foam targets heat volumetrically to an underdense source in less than a nanosecond which can be more efficient. Both the experimental and simulation details of these high fluence x-ray sources will be discussed. [Preview Abstract] |
Monday, October 23, 2017 3:00PM - 3:30PM |
CI3.00003: Systematic measurements of opacity dependence on temperature, density, and atomic number at stellar interior conditions Invited Speaker: Taisuke Nagayama Model predictions for iron opacity are notably different from measurements performed at matter conditions similar to the boundary between the solar radiation and convection zones [J.E. Bailey et al., Nature 517, 56 (2015)]. The calculated iron opacities have narrower spectral lines, weaker quasi-continuum at short wavelength, and deeper opacity windows than the measurements. If correct, these measurements help resolve a decade old problem in solar physics. A key question is therefore: What is responsible for the model-data discrepancy? The answer is complex because the experiments are challenging and opacity theories depend on multiple entangled physical processes such as the influence of completeness and accuracy of atomic states, line broadening, contributions from myriad transitions from excited states, and multi-photon absorption processes. To help determine the cause of this discrepancy, a systematic study of opacity variation with temperature, density, and atomic number is underway. Measurements of chromium, iron, and nickel opacities have been performed at two different temperatures and densities. The collection of measured opacities provides constraints on hypotheses to explain the discrepancy. We will discuss implications of measured opacities, experimental errors, and possible opacity model refinements. ++ Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. [Preview Abstract] |
Monday, October 23, 2017 3:30PM - 4:00PM |
CI3.00004: Laser-Plasma Interactions in Magnetized Environment Invited Speaker: Yuan Shi Propagation and scattering of lasers present new phenomena and applications when the plasma medium becomes magnetized. Starting from mega-Gauss magnetic fields, laser scattering becomes manifestly anisotropic [arXiv 1705.09758]. By arranging beams at special angles, one may be able to optimize laser-plasma coupling in magnetized environment. In stronger giga-Gauss magnetic field, laser propagation becomes modified by relativistic quantum effects [PRA 94.012124]. The modified wave dispersion relation enables correct interpretation of Faraday rotation measurements of strong magnetic fields, as well as correct extraction of plasma parameters from the X-ray spectra of pulsars. In addition, magnetized plasmas can be utilized to mediate laser pulse compression [PRE 95.023211]. Using magnetic resonances, it is not only possible to produce optic pulses of higher intensity, but also possible to amplify UV and soft X-ray pulses that cannot be compressed using existing technology. [Preview Abstract] |
Monday, October 23, 2017 4:00PM - 4:30PM |
CI3.00005: A Plasma Based Beam Combiner for Very High Fluence and Energy Invited Speaker: Robert Kirkwood Recent work at NIF has demonstrated a plasma-based optic that combines the energy and fluence of many laser beams into a single bright beam, thus creating a new technique for designing future high energy density physics experiments. The technique uses the Cross Beam Energy Transfer (CBET) process [1] and shows for the first time that a plasma can combine beams to produce a single beam that emerges with energy and fluence beyond that of any of those input for delivery to a range of experimental targets. In an initial demonstration multiple beams of the National Ignition Facility (NIF) laser have been combined in a plasma to produce a directed pulse of light with 4 \underline {}$+$\underline { }1 kJ of energy in its 1 ns duration which is 3.6 times the energy and 3.2 times the fluence of any of the incident beams during that period and is NIFs brightest 1ns duration beam of UV light [2]. These enhancements are due to the non-linear interaction of the beams with a self-generated plasma diffractive optic which is far more damage resistant than existing solid state optics, and is inherently capable of producing much higher single beam fluence and radiance than solid state refractive or reflective optics can. The initial results are presently being used to further validate models of CBET [3] which predict a larger number of non-resonant pump beams will scale up outputs still further. [1] R. K. Kirkwood et al Plasma Phys. Control. Fusion 55, 103001 (2013). [2] R. K. Kirkwood et al submitted to Nature Physics. [3] D. Turnbull et al Phys. Rev. Lett. 118, 015001 (2017). [Preview Abstract] |
Monday, October 23, 2017 4:30PM - 5:00PM |
CI3.00006: Laser-driven strong magnetostatic fields with applications to charged beam transport and magnetized high energy-density physics Invited Speaker: Joao Santos Powerful laser-plasma processes are explored to generate discharge currents of a few 100 kA in coil targets, yielding magnetostatic fields (B-fields) in the \textasciitilde kTesla range. The B-fields are measured by proton-deflectometry and high-frequency bandwidth B-dot probes [New J. Phys. \textbf{17}, 083051 (2015); App. Phys. Lett. \textbf{108}, 091104 (2016)]. According to our modeling [Phys. Rev. E (2017, submitted)], the quasi-static currents are provided from hot electron ejection from the laser-irradiated surface, accounting for the space charge neutralization and the plasma magnetization. The major control parameter is the laser irradiance $I\lambda^{\mathrm{2}}$. The B-fields ns-scale is long enough to magnetize secondary targets through resistive diffusion. We applied it in experiments of laser-generated relativistic electron transport into solid dielectric targets, yielding an unprecedented enhancement of a factor 5 on the energy-density flux at 60~\textmu m depth, compared to unmagnetized transport conditions [Nat. Comm. (2017, submitted), arXiv:1608.08101]. These studies pave the ground for magnetized high-energy density physics investigations, related to laser-generated secondary sources of radiation and/or high-energy particles and their transport, to high-gain fusion energy schemes and to laboratory astrophysics. [Preview Abstract] |
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