Bulletin of the American Physical Society
52nd Annual Meeting of the APS Division of Plasma Physics
Volume 55, Number 15
Monday–Friday, November 8–12, 2010; Chicago, Illinois
Session TO5: Hydrodynamic Instability |
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Chair: Max Karasik, Naval Research Laboratory Room: Grand Ballroom B |
Thursday, November 11, 2010 9:30AM - 9:42AM |
TO5.00001: High resolution simulations of ignition capsule designs for the National Ignition Facility Daniel Clark, Steven Haan, Bruce Hammel, Michael Marinak, Richard Town Ignition capsule designs for the National Ignition Facility (NIF) continue to evolve in light of improved physical data inputs, improving simulation techniques, and--most recently--experimental data from recent NIF sub-ignition experiments. This talk summarizes a number of recent changes to the cryogenic capsule design and some of our latest techniques in simulating its performance. Foremost, experiments have indicated harder x-ray drive spectra in NIF hohlraums than were predicted and used for previous capsule optimization studies. To accommodate this harder spectrum, the germanium ablator dopant concentration has been re-optimized based on a series of high resolution 2-D simulations resolving Legendre mode numbers as high as two thousand. Second, concern over the possibility of cooperative or nonlinear interaction of isolated defects on the ablator surface has motivated a series of fully 3-D capsule simulations. These simulations can use actual measured shell surfaces as initial conditions and include resolution to mode two hundred or higher. [Preview Abstract] |
Thursday, November 11, 2010 9:42AM - 9:54AM |
TO5.00002: Mix in Omega and NIF Capsules with an Eulerian Code Paul Bradley, G. Magelssen, M. Schmitt, E. Dodd, S. Hsu, F. Wysocki, I. Tregillis, S. Finnegan, K. DeFriend Obrey There is much evidence that mixing of capsule shell material into the DT fuel in ICF capsules significantly reduces the nuclear yield. Mix occurs as a result of capsule manufacturing tolerances that grow during the implosion. Additional mix will occur if defects, such as cracks or material inhomogeneities, are present. Verifying the predictive capabilities of our codes for mix and defects is a crucial part of achieving robust ignition on NIF. We are performing a series of simulations to assess the influence of feature driven mix on the performance of Omega capsules. Our usage of a subgrid turbulent mix model allows us to obtain neutron yields within a factor of 2 to 6 of the Omega data. We will present results of these simulations along with predictions for follow-on experiments that will be performed on NIF in the near future. [Preview Abstract] |
Thursday, November 11, 2010 9:54AM - 10:06AM |
TO5.00003: The Effect of Nonuniformity Growth on Direct-Drive Plastic-Shell Implosions on the OMEGA Laser P.B. Radha, C. Stoeckl, J.P. Knauer, V.N. Goncharov, I.V. Igumenshchev, R.L. McCrory, D.D. Meyerhofer, T.C. Sangster, S. Skupsky, J.A. Frenje, R.D. Petrasso The in-flight aspect ratio (IFAR)---the ratio of the shell radius to its thickness---is an important implosion parameter that defines the minimum energy required for ignition and characterizes nonuniformity growth. Target performance is systematically studied in deuterium-filled warm plastic-shell implosions using triple-picket laser pulses on the OMEGA Laser. Picket energies and the timing between the pickets are systematically varied to obtain IFAR's between 30 and 60. Observed yields increase by nearly a factor of 3 when the IFAR is reduced to 30 from 60. A nearly 1-D value of areal density, $\langle $\textit{$\rho $R}$\rangle \quad \sim $ 170~mg/cm$^{2}$, is observed for IFAR $\sim $ 30. Observed $\langle $\textit{$\rho $R}$\rangle $ is significantly reduced from 1-D values for IFAR $\sim $ 60, with a value $\sim $140 mg/cm$^{2}$. These observations demonstrate the scaling of direct-drive target performance with IFAR. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC52-08NA28302. [Preview Abstract] |
Thursday, November 11, 2010 10:06AM - 10:18AM |
TO5.00004: Impact of Laser Plasma Instability Induced Intensity Limitations on Target Design Andrew J. Schmitt, D.E. Fyfe, S.P. Obenschain, S.T. Zalesak ICF direct-drive targets perform best when the pressure of the driving pulse is maximized: the targets can then be designed with small aspect ratios that are more hydrodynamically stable. However the drive pressure in direct drive targets is limited by laser plasma instabilities, which must be avoided to limit unwanted preheat of the fusion fuel. In direct drive, the instability with the lowest threshold is the two plasmon decay instability, which experiments have so far shown to be approximated by the simple formula\footnote{A. Simon, \textit{et al.}, Phys. Fluids \textbf{26}, 3107 (1983); B. Afeyan and E.A. Williams, Phys. Plasmas \textbf{4}, 3827 (1997).} $I_{thresh} \sim 80\ T_{keV}/\lambda_{\mu m}L_{\mu m}$ where T and L are the electron temperature and density scalelength at the quarter critical surface, and $\lambda$ is the laser wavelength. Limiting the intensity to this threshold can be done by increasing the target aspect ratio and/or increasing the collisionality of the ablator. We investigate the implications of these strategies on hydro stability and target design, for both glass laser and KrF-laser driven targets. [Preview Abstract] |
Thursday, November 11, 2010 10:18AM - 10:30AM |
TO5.00005: Analysis of ICF Capsule Surfaces Using Modal Growth Factors Joseph Ralph, M.J. Edwards, J.L. Milovich, S.V. Weber, N.B. Meezan, S.W. Haan, M.A. Johnson, P.T. Springer, B.A. Hammel, S.H. Glenzer Perturbations on an ICF capsule ablator surface can seed Rayleigh-Taylor instability, which can lead to ablator material being injected into the hot spot, cooling it by radiation. If sufficient mass is injected, the radiative energy loss can be sufficient to quench ignition. Modal growth factors derived from hydrodynamic simulations applied directly to the metrologized surfaces of CH capsules has proven to be a valuable tool for predicting the amount of ablator mass that would be injected into the hot spot, as well as providing a visualization the overall shell integrity during the implosion in 3D. The results of the application of this technique to Symcap and THD NIF implosion targets with comparison to gated x-ray shot data will be presented. The pulse shapes for different drive conditions have resulted, from hydrodynamic simulations, in vastly different modal growth factors. The application of these modal growth factors will be shown to help in optimizing the pulse shapes and minimize Rayleigh-Taylor growth. Comparison with hydrodynamic simulations will be shown. 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] |
Thursday, November 11, 2010 10:30AM - 10:42AM |
TO5.00006: Modeling of NIC Symcap and THD Experiments Using High Resolution Integrated Hohlraum-Capsule Simulations Ogden Jones, Jose Milovich, Marty Marinak, Scott Sepke, Mehul Patel, Nathan Meezan, Deborah Callahan, Richard Town, Siegfried Glenzer, Marilyn Schneider, Steve Langer, Dave Munro, Brian Spears, Paul Springer, John Edwards, Doug Wilson, George Kyrala, John Kline We have developed a capability to do very high spatial resolution 2D integrated hohlraum-capsule simulations using the Hydra code. Surface perturbations for all ablator layer surfaces and the DT ice layer are calculated explicitly up to mode 30 or 100. The effects of the fill tube, grooves in the ice layer, and surface defects on the ablator are included via models extracted from higher resolution calculations. High wave number mix is included through a mix model. Measured backscatter and a model for crossbeam energy transfer are included to enable a best estimate of the drive asymmetry for each shot. We have applied this model to National Ignition Campaign (NIC) experiments from the fall of 2009 and more recent symmetry capsule and cryogenic layered tritium-hydrogen-deuterium (THD) experiments. We compare the measured x-ray and neutron diagnostic signatures to the simulated diagnostic signatures extracted from the model. [Preview Abstract] |
Thursday, November 11, 2010 10:42AM - 10:54AM |
TO5.00007: Assessment of radiography for diagnosing short wavelength instability growth and mix in NIF ignition capsules Kyle Peterson, Roger Vesey, Mark Herrmann, Dan Clark, Larry Suter, Bruce Hammel, Steve Haan, Otto Landen Understanding and controlling hydrodynamic instabilities is critical to achieving ignition at National Ignition Facility (NIF). High resolution x-ray radiography of a NIF capsule may be able to measure key aspects of short wavelength instability growth including time dependent areal density variations, the dominant wavelength of growth, amount of growth from isolated capsule defects on the ablator and ice surfaces, and growth of perturbations as a result of the fill tube or dust contaminants. Radiography of the capsule limb may also place constraints on the width of the ice/ablator mix layer. Measurement of these various observables are important to determine what effect target design changes has on instability growth and to validate code predictions. We present an analysis of 2D and 3D HYDRA simulations and demonstrate how radiography can be used to diagnose signatures of mix in NIC capsules. [Preview Abstract] |
Thursday, November 11, 2010 10:54AM - 11:06AM |
TO5.00008: Smoothing by Spectral Dispersion (SSD) for Multiple-Picket Pulses on OMEGA and the NIF J.A. Marozas, J.D. Zuegel, T.J.B. Collins Recent target designs (for both OMEGA and the NIF) use multiple-picket pulses that are better suited to experimental shock tuning. The short time duration of the pickets poses numerous challenges in designing an optimal beam-smoothing system: (1) laser imprint can occur in multiple short time periods; (2) SSD continuously repositions the energy centroid of the focal spot (effectively mispointing all spots on target in synchronization), which can be considerable when there is not adequate bandwidth dispersion across the beam; and (3) a temporal shear imposed on the beam by NIF's SSD system could substantially distort the picket shape. These aspects of SSD for multiple-picket pulses are examined using 2-D \textit{DRACO} hydrodynamic simulations with imprint for both OMEGA and NIF target designs. A 1-D Multi-FM SSD design that resolves these issues is proposed and will be tested on OMEGA EP before deployment on the NIF. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC52-08NA28302. [Preview Abstract] |
Thursday, November 11, 2010 11:06AM - 11:18AM |
TO5.00009: Numerical Investigation of the Effect of Two-Plasmon-Decay Electron Preheat in Planar Rayleigh--Taylor Experiments J.A. Delettrez, S.X. Hu, A. Shvydky Planar Rayleigh--Taylor (RT) experiments carried out at laser intensities near 10$^{15}$~W/cm$^{2}$ showed RT growth suppression for the 20-\textit{$\mu $}m-wavelength mode but not for longer wavelength modes.\footnote{V. A. Smalyuk \textit{et al.}, Phys. Rev. Lett. \textbf{101}, 025002 (2008).} This RT growth stabilization was attributed mainly to the nonlocal transport of coronal electrons with only minor estimated preheat from two-plasmon-decay (TPD) electrons. Simulations have been performed with the 2-D hydrodynamics code \textit{DRACO} in which the TPD electrons' preheat is modeled with a straight-line transport package. The effect of the TPD electron preheat on the RT amplitudes for 20-, 30- and 60-\textit{$\mu $}m wavelengths are presented for intensities 5 $\times $ 10$^{14}$ and 10$^{15}$ W/cm$^{2}$. Comparisons with experiments will elucidate the role of TPD electron preheat to the RT-stabilization mechanism. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC52-08NA28302. [Preview Abstract] |
Thursday, November 11, 2010 11:18AM - 11:30AM |
TO5.00010: The Equation-of-State Dependence of Nonuniformity Growth in Cryogenic-DT Implosions on OMEGA S.X. Hu, V.N. Goncharov, T.R. Boehly, S. Skupsky, T.C. Sangster, D.D. Meyerhofer, R.L. McCrory This work reports on the analysis of low-adiabat, cryogenic deuterium--tritium (DT), high-compression implosion experiments\footnote{ V. N. Goncharov \textit{et al}., Phys. Rev. Lett. \textbf{104}, 165001 (2010).} performed on OMEGA using 2-D \textit{DRACO} simulations.\footnote{ S. X. Hu\textit{ et al}., ``Two-Dimensional Simulations of the Neutron-Yield in Cryogenic-DT Implosions on OMEGA,'' submitted to Phys. Plasmas.} The growth of various target and laser perturbations has been investigated using 2-D radiation-hydrodynamic simulations with different fuel equation-of-states (EOS) such as the \textit{SESAME}-EOS, the Thomas--Fermi model, as well as the FPEOS table\footnote{ S. X. Hu\textit{ et al}., Phys. Rev. Lett. \textbf{104}, 235003 (2010).} recently created by the path-integral Monte Carlo method. It has been shown that uniform 1-D hydro simulations using the FPEOS table predicted $\sim $20{\%} lower neutron yield than the \textit{SESAME}-EOS case.$^{3}$ In this work, we will present the dependence of RT growth and neutron-yield reduction on these different equation of states from 2-D hydro simulations. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC52-08NA28302. [Preview Abstract] |
Thursday, November 11, 2010 11:30AM - 11:42AM |
TO5.00011: Measuring the Ablative Richtmyer-Meshkov Growth of Isolated Defects on Plastic Capsules Eric Loomis, Dave Braun, Steve Batha, Tom Sedillo, Scott Evans, Chuck Sorce, Otto Landen To achieve thermonuclear ignition at Megajoule class laser systems such as the NIF using inertially confined plasmas, targets must be designed with high in-flight aspect ratios (IFAR) resulting in low shell stability. Recent simulations and experiments have shown that isolated features on the outer surface of an ignition capsule can profoundly impact capsule performance by leading to material jetting or mix into the hotspot. Unfortunately, our ability to accurately predict these effects is uncertain due to disagreement between equation of state (EOS) models. In light of this, we have begun a campaign to measure the growth of isolated defects due to ablative Richtmyer-Meshkov in CH capsules to validate these models. Face- on transmission radiography has been used to measure the evolution of Gaussian bump arrays in plastic targets. Targets were indirectly-driven using Au halfraums to radiation temperatures near 65-75 eV at the Omega laser (Laboratory for Laser Energetics, University of Rochester, NY) simultaneous with x-ray backlighting from a saran (Cl) foil. Shock speed measurements were also made to determine drive conditions in the target. The results from these experiments will aid in the design of ignition drive pulses that minimize bump amplitude at the time of shell acceleration. [Preview Abstract] |
Thursday, November 11, 2010 11:42AM - 11:54AM |
TO5.00012: Richtmyer-Meshkov Instability Growth Studies in Ion Beam Driven HEDP Experiments Naeem A. Tahir, Alexander Shutov, I.V. Lomonosov, A.R. Piriz, Thomas Stoehlker, Claude Deutsch A Mach type reflection scheme has been used to generate a plane shock wave using a wedge shaped multi-layered target irradiated by an intense heavy ion beam. The shock wave is allowed to pass through a corrogated bounday to study the Richtmyer-Meshkov instability. Numerical simulations show that one can study the instability growth in linear and non-linear regime in fluids as well as solids. [Preview Abstract] |
Thursday, November 11, 2010 11:54AM - 12:06PM |
TO5.00013: The evolution of the instabilities during magnetically driven cylindrical liner implosions Stephen Slutz, Daniel Sinars, Ryan McBride, Roger Veseys, Mark Herrmann, Michael Cuneo Numerical simulations [S.A. Slutz et al Phys. Plasmas 17, 056303 (2010)] indicate that fuel magnetization and preheat could enable cylindrical liner implosions to become an efficient means to generate fusion conditions. A series of simulations has been performed to study the stability of magnetically driven liner implosions. These simulations exhibit the initial growth and saturation of an electro-thermal instability. The Rayleigh-Taylor instability further amplifies the resultant density perturbations developing a spectrum of modes initially peaked at short wavelengths. With time the spectrum of modes evolves towards longer wavelengths developing an inverse cascade. The effects of mode coupling, the radial dependence of the magnetic pressure, and the initial surface roughness will be discussed. [Preview Abstract] |
Thursday, November 11, 2010 12:06PM - 12:18PM |
TO5.00014: Regularization mechanism of Rayleigh-Taylor turbulent mixing Snezhana I. Abarzhi Turbulent mixing induced by Rayleigh-Taylor instability plays an crucial role in a variety of high energy density phenomena spanning astrophysical to atomistic scales, including inertial confinement fusion, supernovae, and interstellar molecular clouds. We apply group theory to analyze symmetries, invariants, scaling and spectra of turbulent mixing induced by the Rayleigh-Taylor instability. The properties of this unsteady, anisotropic, and inhomogeneous turbulent process are found to depart from the canonical Kolmogorov scenario. Time- and scale-invariance of the rate of momentum loss leads to non-dissipative momentum transfer between the scales, to 1/2 and 3/2 power-law scale-dependencies of the velocity and Reynolds number respectively, and to spectra distinct from Kolmogorov. Turbulent mixing exhibits more order compared to isotropic turbulence and its viscous and dissipation scales are set by the flow acceleration. To trigger relaminarization of RT mixing, few mechanisms are proposed, including coherence of the initial conditions and the flow acceleration with high favorable pressure gradient. [Preview Abstract] |
Thursday, November 11, 2010 12:18PM - 12:30PM |
TO5.00015: Field compressing magneto-thermal instability in laser heated plasma Robert Kingham, John Bissell, Christopher Ridgers We present a new instability in magnetized long scale-length plasmas heated by laser beams. It is active under conditions of recent nanosecond laser gas-jet experiments [1] - with collinear laser beam and applied B-field - designed to explore transport issues in magnetized laser-plasmas and in ICF, particularly hohlraum plasmas. The instability is driven by cross-field heat-flow out of the laser-heated column and leads to growth of large B-field and temperature perturbations (perpendicular to the field direction and bulk .$\nabla $T). Unstable behaviour results purely from transport processes - feedback between the Nernst effect and the Righi-Leduc heat-flow phenomena in particular - neither hydrodynamic motion nor density gradients are essential. The phenomena is distinct from other well known instabilities such as the Tidman-Shanny, Weibel and the MHD interchange instabilities. Calculations based on [1] predict a peak growth rate of order 10 ns$^{-1}$ at wavelengths of order 50 $\mu $m, for a 6T field and n$_{e}$=1.5x10$^{19}$ cm$^{-3}$. The strong modulation in the B-field strength affects the spread of thermal energy from the heated region. \\[4pt] [1] D. Froula, \textit{et al.}, PRL \textbf{98} (135001) 2007 [Preview Abstract] |
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