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 CO5: Hohlraums II |
Hide Abstracts |
Chair: Denise Hinkel, Lawrence Livermore National Lab Room: 230 B |
Monday, October 31, 2016 2:00PM - 2:12PM |
CO5.00001: Electron Temperature and Plasma Flow Measurements of NIF Hohlraum Plasmas M. A. Barrios, D. A. Liedahl, M. B. Schneider, O. Jones, G. V. Brow, S. P. Regan, K. B. Fournier, A. S. Moore, J. S. Ross, D. Eder, O. Landen, R. L. Kauffman, A. Nikroo, J. Kroll, J. Jaquez, H. Huang, S. B. Hansen, D. A. Callahan, D. E. Hinkel, D. Bradley, J. D. Moody Characterizing the plasma conditions inside NIF hohlraums, in particular mapping the plasma T$_{\mathrm{e}}$, is critical to gaining insight into mechanisms that affect energy coupling and transport in the hohlraum. The dot spectroscopy platform provides a temporal history of the localized T$_{\mathrm{e\thinspace }}$and plasma flow inside a NIF hohlraum, by introducing a Mn-Co tracer dot, at strategic locations inside the hohlraum, that comes to equilibrium with the local plasma. K-shell X-ray spectroscopy of the tracer dot is recorded onto an absolutely calibrated X-ray streak spectrometer. Isoelectronic and interstage line ratios are used to infer localized T$_{\mathrm{e}}$ through comparison with atomic physics calculations using SCRAM [S.B. Hansen, \textit{et al.} High Energy Density Phys. \textbf{3}, 109 (2007)]. Time resolved X-ray images are simultaneously taken of the expanding dot, providing plasma (ion) flow information. We present recent results provided by this platform and compare with simulations using HYDRA [Marinak, \textit{et al., }Phys. Plasmas \textbf{3}, 2070 (1996)]. This work was performed under the auspices of the U.S. Department of Energy by LLNL under Contract DE-AC52-07NA27344. [Preview Abstract] |
Monday, October 31, 2016 2:12PM - 2:24PM |
CO5.00002: On the hydrodynamics of dot spectroscopy experiments at the National Ignition Facility Olivier Poujade The dot spectroscopy [M. A. Barrios et al., PoP 23, 056307 (2016)] platform was developed in the context of indirect-drive Inertial Confinement Fusion at the NIF in order to assess the electron temperature of the plasma within the hohlraum. The possibility of a mixing between the tracer-dot and the ablator is advocated on theoretical ground and with help from dedicated numerical simulations of shots N141216 (0.8$\times$ scaled hohlraum, gas filled with neopentane at 1.37 mg/cm$^3$) and N150427 (full scale hohlraum, gas filled with helium at 0.96 mg/cm$^3$). So far, all simulations (LLNL and CEA) of this platform were integrated and the possibility of a mixing was inhibited by the lack of resolution. Refined simulations of the region around the tracer-dot and the ablator, subjected to the correct irradiation versus time, show that mixing might occur very early in the course of the drive and would be caused by classical Rayleigh-Taylor instability at the interface between the tracer-dot and the ablator. This effect seems to contribute significantly to the glaring discrepancy between integrated simulations and experiments with respect to the dot location (off by 200 $\mu$m) and with respect to the electron temperature (off by 500 eV). [Preview Abstract] |
Monday, October 31, 2016 2:24PM - 2:36PM |
CO5.00003: Experimental characterization of NIF hohlraum emission in the Rayleigh-Jeans limit (1 eV to 5 eV) J. D. Moody, C. E. Goyon, J. S. Ross, G. F. Swadling, A. S. Moore, K. L. Baker, C. A. Thomas, M. B. Schneider, O. L. Landen, P. A. Michel, D. J. Strozzi, L. Divol, K. Widmann We use several measurements to estimate NIF hohlraum emission in the Rayleigh-Jeans limit where $h\nu << kT_R$ and $T_R$ is the hohlraum radiation temperature which is typically $\approx$ 260 to 300 eV. The measurements are primarily optical, consisting of hohlraum emission which transmits through the capsule and is collected by an optical photodiode, optical emission emitted from the laser-entrance hole in the 4 eV range, and various other optical measurements. These measurements can help quantify the laser-plasma interaction processes occurring in the hohlraum and may provide insight into the atomic physics of the Au wall at long wavelength. We describe our findings and discuss interpretations. [Preview Abstract] |
Monday, October 31, 2016 2:36PM - 2:48PM |
CO5.00004: Results From the New NIF Gated LEH imager Hui Chen, P. Amendt, M. Barrios, D. Bradley, D. Casey, D. Hinkel, L. Berzak Hopkins, J. Kilkenny, A. Kritcher, O. Landen, O. Jones, T. Ma, J. Milovich, P. Michel, J. Moody, J. Ralph, A. Pak, N. Palmer, M. Schneider A novel ns-gated Laser Entrance Hole (G-LEH) diagnostic has been successfully implemented at the National Ignition Facility (NIF). ~This diagnostic has successfully acquired images from various experimental campaigns, providing critical information for inertial confinement fusion experiments. The G-LEH diagnostic which takes time-resolved gated images along a single line-of-sight, incorporates a high-speed multi-frame CMOS x-ray imager developed by Sandia National Laboratories into the existing Static X-ray Imager diagnostic at NIF. It is capable of capturing two laser-entrance-hole images per shot on its 1024x448 pixel photo-detector array, with integration times as short as 2 ns per frame. The results that will be presented include the size of the laser entrance hole vs. time, the growth of the laser-heated gold plasma bubble, the change in brightness of inner beam spots due to time-varying cross beam energy transfer, and plasma instability growth near the hohlraum wall. [Preview Abstract] |
Monday, October 31, 2016 2:48PM - 3:00PM |
CO5.00005: Analysis of data from gold spheres imbedded in a gas bag, illuminated by the URLLE Omega laser Mordecai Rosen, J. S. Ross, G. Swadling, D. E. Hinkel, C. Thomas, D. Callahan, O. Jones, G. B. Zimmerman In order to make data from an open Au sphere (previously shot in 2006 and 2013) more ``hohlraum relevant'', we embedded the sphere in a ``gas bag'', comprised of a thin membrane filled with varying amounts of gas. The Thomson Scattering (TS) data from this new campaign gave clear signatures of when the Au expanded out within this surrounding gas to a given radial point at a given time. We analyze this data via radiation-hydrodynamic simulations that include a post-processor that directly mimics the TS spectra vs. time. Within these simulations, we test various non-LTE atomic physics models, as well as electron transport models. One model that appears to fit this new data is a restrictive flux limiter, mimicking the ``Return-Current-Instability''(RCI) which, when operative, is effectively f$=$0.015. The same ion acoustic turbulence (an outgrowth of the RCI), that enhances scattering, and thus inhibits transport, can also increase absorption. This increase in absorption, applied (speculatively) close by the critical surface, is part of the computational model. This same model showed some success with the bare Au sphere data as well, as reported at APS/DPP last year. We also discuss ion diffusion effects. [Preview Abstract] |
Monday, October 31, 2016 3:00PM - 3:12PM |
CO5.00006: Structure and dynamics of plasma interfaces in laser-driven hohlraums}$^{\mathrm{\mathbf{\ast }}}$ C. K. Li, H. Sio, J. A. Frenje, F. H. S\'eguin, A. Birkel, R. D. Petrasso, S. C. Wilks, P. A. Amendt, B. A. Remington, P.-E. Masson-Laborde, S. Laffite, V. Tassin, R. Betti, T. C. Sanster, P. Fitzsimmons, M. Farrell Understanding the structure and dynamics of plasma interfaces in laser-driven hohlraums is important because of their potential effects on capsule implosion dynamics. To that end, a series of experiments was performed to explore critical aspects of the hohlraum environment, with particular emphasis on the role of self-generated spontaneous electric and magnetic fields at plasma interfaces, including the interface between fill-gas and Au-blowoff. The charged fusion products (3-MeV DD protons and 14.7-MeV D$^{\mathrm{3}}$He protons generated in shock-driven, D$^{\mathrm{3}}$He filled backlighter capsule) pass through the subject hohlraum and form images on CR-39 nuclear track detectors, providing critical information. Important physics topics, including ion diffusive mix and Rayleigh-Taylor instabilities, will be studied to illuminate ion kinetic dynamics and hydrodynamic instability at plasma interfaces in laser-driven hohlraums. [Preview Abstract] |
Monday, October 31, 2016 3:12PM - 3:24PM |
CO5.00007: Effects of self-generated magnetic fields on hohlraum simulation at NIF W. A. Farmer, D. J. Strozzi, D. E. Hinkel, M. D. Rosen, O. S. Jones, J. M. Koning, M. M. Marinak Non-parallel density and pressure gradients that develop during matter ablation on a laser irradiated target lead to self-generated magnetic fields through the well-known Biermann-battery effect. For laser intensities present during ICF relevant scenarios on NIF, megagauss fields can develop. The presence of large magnetic fields leads to a non-negligible Hall parameter, defined as the product of the electron cyclotron frequency and the electrion-ion collision time. When the Hall parameter is of order unity or greater, a significant reduction in the cross-field heat flux occurs. Large magnetic fields are limited by the inclusion of the Nernst term, which advects the magnetic fields in the direction of the heat flux (or from the ablation front into the denser wall). This advection combined with resistive diffusion of the magnetic field limits the strength of the self-generated field within the hohlraum. We report changes in simulation results obtained when using the MHD package in the radiation-hydrodynamics code, HYDRA, which models the evolutions of the magnetic fields. [Preview Abstract] |
Monday, October 31, 2016 3:24PM - 3:36PM |
CO5.00008: Quantitative Analysis of Hohlraum Energetics Modeling Mehul V. Patel, Christopher W. Mauche, Odgen S. Jones, Howard A. Scott New 1D/2D hohlraum models have been developed to enable quantitative studies of ICF hohlraum energetics. The models employ sufficient numerical resolution (spatial, temporal discetization, radiation energy groups, laser rays, IMC photons) to satisfy {\it a priori} convergence criteria on the observables to be compared. For example, we aim for numerical errors of less than 5\% in the predicted X-ray flux. Post shot simulations using the new models provide quantitative assessments of the accuracy of energetics modeling across a range of ICF platforms. The models have also been used to reexamine physics sensitivities in the modeling of the NLTE wall plasma. This work is guiding improvements in the underlying DCA atomic physics models and the radiation hydrodynamics code (HYDRA). [Preview Abstract] |
Monday, October 31, 2016 3:36PM - 3:48PM |
CO5.00009: Effect of Energetic Electrons Produced by Raman Scattering on Hohlraum Dynamics D. J. Strozzi, D. S. Bailey, T. Doeppner, L. Divol, J. A. Harte, P. Michel, C. A. Thomas A reduced model of laser-plasma interactions, namely crossed-beam energy transfer and stimulated Raman scattering (SRS), has recently been implemented in a self-consistent or ``inline'' way in radiation-hydrodynamics codes$^1$. We extend this work to treat the energetic electrons produced by Langmuir waves (LWs) from SRS by a suprathermal, multigroup diffusion model$^2$. This gives less spatially localized heating than depositing the LW energy into the local electron fluid. We compare the resulting hard x-ray production to imaging data on the National Ignition Facility, which indicate significant emission around the laser entrance hole. We assess the effects of energetic electrons, as well as background electron heat flow, on hohlraum dynamics and capsule implosion symmetry. $^1$D. J. Strozzi et al., Phys. Rev. Lett. (submitted). $^2$D. S. Kershaw, LLNL report UCRL-50021-80, p. 3-78 (1980). [Preview Abstract] |
Monday, October 31, 2016 3:48PM - 4:00PM |
CO5.00010: Enthalpy generation from mixing in hohlraum-driven targets Peter Amendt, Jose Milovich The increase in enthalpy from the physical mixing of two initially separated materials is analytically estimated and applied to ICF implosions and gas-filled hohlraums. Pressure and temperature gradients across a classical interface are shown to be the origin of enthalpy generation from mixing. The amount of enthalpy generation is estimated to be on the order of 100 Joules for a 10 micron-scale annular mixing layer between the solid deuterium-tritium fuel and the undoped high-density carbon ablator of a NIF-scale implosion. A potential resonance is found between the mixing layer thickness and gravitational ($C_{\mathrm{s}}^{\mathrm{2}}$/$g)$ and temperature-gradient scale lengths, leading to elevated enthalpy generation. These results suggest that \textit{if} mixing occurs in current capsule designs for the National Ignition Facility, the ignition margin may be appreciably eroded by the associated enthalpy of mixing. The degree of enthalpy generation from mixing of high-$Z$ hohlraum wall material and low-$Z$ gas fills is estimated to be on the order of 100 kJ or more for recent NIF-scale hohlraum experiments, which is consistent with the inferred missing energy based on observed delays in capsule implosion times [1]. [1] O.S. Jones \textit{et al}., Phys. Plasmas 19, 056315 (2012). [Preview Abstract] |
Monday, October 31, 2016 4:00PM - 4:12PM |
CO5.00011: Improving the accuracy of hohlraum simulations by calibrating the `SNB' multigroup diffusion model for nonlocal heat transport against a VFP code Jonathan Brodrick, Christopher Ridgers, Ben Dudson, Robert Kingham, Marty Marinak, Mehul Patel, Maxim Umansky, Alex Chankin, John Omotani Nonlocal heat transport, occurring when temperature gradients become steep on the scale of the electron mean free path (mfp), has proven critical in accurately predicting ignition-scale hohlraum energetics. A popular approach, and modern alternative to flux limiters, is the `SNB' model\footnote{Schurtz \emph{et al.} \textbf{Phys. Plasmas} 7, 4238 (2000)}. This is implemented in both the HYDRA code used for simulating National Ignition Facility experiments and the CHIC code developed at the CELIA laboratory. We have performed extensive comparisons of the SNB heat flow predictions with two VFP codes, IMPACT\footnote{Kingham \& Bell \textbf{J. Comp. Phys.} 194 (2004)} and KIPP\footnote{Chankin \emph{et al.} \textbf{Contrib. Plasma Phys.} 52, 500 (2012)} and found that calibrating the mfp to achieve agreement for a linear problem also improves nonlinear accuracy. Furthermore, we identify that using distinct electron-ion and electron-electron mfp's instead of a geometrically averaged one improves predictive capability when there are strong ionisation ($Z$) gradients. [Preview Abstract] |
Monday, October 31, 2016 4:12PM - 4:24PM |
CO5.00012: Does laser-driven heat front propagation depend on material microstructure? J. D. Colvin, H. Matsukuma, K. B. Fournier, A. Yoga, G. E. Kemp, N. Tanaka, Z. Zhang, K. Kota, S. Tosaki, T. Ikenouchi, H. Nishimura We showed earlier that the laser-driven heat front propagation velocity in low-density Ti-silica aerogel and TiO$_{\mathrm{2}}$ foam targets was slower than that simulated with a 2D radiation-hydrodynamics code incorporating an atomic kinetics model in non-LTE and assuming initially homogeneous material (F. P\'{e}rez, et al., Physics of Plasmas 21, 023102, 2014). Some theoretical models suggest that the heat front is slowed over what it would be in a homogeneous medium by the microstructure of the foam. In order to test this hypothesis we designed and conducted a comparison experiment on the GEKKO laser to measure heat front propagation velocity in two targets, one an Ar/CO$_{\mathrm{2}}$ gas mixture and the other a TiO$_{\mathrm{2}}$ foam, that had identical initial densities and average ionization states. We found that the heat front traveled about ten times faster in the gas than in the foam. We present the details of the experiment design and a comparison of the data with the simulations. [Preview Abstract] |
Monday, October 31, 2016 4:24PM - 4:36PM |
CO5.00013: Measuring the Refractive Index of a Laser-Plasma Optical System D. Turnbull, C. Goyon, B.B. Pollock, D. Mariscal, L. Divol, J.S. Ross, S. Patankar, G.E. Kemp, J.D. Moody, P.A. Michel We report the first complete set of measurements of a laser-plasma optical system's refractive index, as seen by an independent probe laser beam, as a function of the relative wavelength shift between the two laser beams. Both the imaginary and real refractive-index components are found to be in good agreement with linear theory using plasma parameters measured by optical Thomson scattering and interferometry; the former is in contrast to previous work and has implications for cross-beam energy transfer in indirect-drive inertial confinement fusion, and the latter is measured for the first time. The data include the first demonstration of a laser-plasma polarizer with 85{\%} to 87{\%} extinction for the particular laser and plasma parameters used in this experiment, complementing the existing suite of high-power, tunable, and ultrafast plasma-based photonic devices. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. [Preview Abstract] |
Monday, October 31, 2016 4:36PM - 4:48PM |
CO5.00014: ABSTRACT WITHDRAWN |
Monday, October 31, 2016 4:48PM - 5:00PM |
CO5.00015: Measurements of Anisotropy in Non-LTE Low-Density, Iron-Vanadium Plasmas L. C. Jarrott, M. E. Foord, R. F. Heeter, D. A. Liedahl, M. A. Barrios, G. V. Brown, W. Gray, E. V. Marley, C. W. Mauche, K. Widmann, M. B. Schneider We report on Non-LTE anisotropy experiments carried out on the Omega Laser Facility at the Laboratory for Laser Energetics, Rochester NY. In these experiments, a 50/50 mixture of iron and vanadium, 2000A thick and 250um in diameter is contained within a beryllium tamper, 10um thick and 1000um in diameter. Each side of the beryllium tamper is then irradiated using 52 of the 60 Omega beams with an intensity of 3e14 W/cm$^{\mathrm{2}}$ over 3ns in duration. Iron-Vanadium line ratios indicate a plasma temperature of greater than 2 keV was produced. The geometrical aspect ratio ranged from 0.8 to 4.0; allowing for the characterization of optical-depth-dependent anisotropy in the iron-vanadium line emission. Results of this characterization and its comparison with modeling will be presented. This work performed under the auspices of U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700