Bulletin of the American Physical Society
54th Annual Meeting of the APS Division of Plasma Physics
Volume 57, Number 12
Monday–Friday, October 29–November 2 2012; Providence, Rhode Island
Session TO4: Mix and Hydro Instabilities |
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Chair: Radha Bahukutumbi, University of Rochester Room: 551AB |
Thursday, November 1, 2012 9:30AM - 9:42AM |
TO4.00001: Recent results of the Defect-Induced Mix Experiments (DIME) on NIF M.J. Schmitt, P.A. Bradley, J.A. Cobble, P. Hakel, S.C. Hsu, N.S. Krasheninnikova, G.A. Kyrala, T.J. Murphy, K.A. Obrey, R.C. Shah, I.L. Tregillis, S.C. Craxton, P.W. McKenty, R.C. Mancini, H.M. Johns, Tirtha Joshi, Daniel Mayes Investigations of directly driven implosions have been performed including experiments on Omega, and more recently NIF, to deduce the extent and uniformity of 4$\pi $ and defect-induced mix near the shell/gas interface of plastic (CH) capsules filled with 5 atm D$_{2}$ gas. Imaging diagnostics are used to measure the spatial variation of mix caused by the growth of non-uniformities in both capsule and laser drive characteristics. Thin (2$\mu $m) layers containing 1-2{\%} (atomic) mid-Z dopants are imaged spectrally at late time in the implosion using multiple monochromatic imaging of H-like and He-like atomic line emission. Areal image backlighting of the capsules provides both $r(t)$ and the symmetry of the implosion. Recent results will be shown including inferred 4$\pi $ mix width, laser imprint induced mix, and mix from capsule variations. [Preview Abstract] |
Thursday, November 1, 2012 9:42AM - 9:54AM |
TO4.00002: Polar Direct-Drive Plastic Capsule Implosions for Studying Mix on the National Ignition Facility T.J. Murphy, G.A. Kyrala, P.A. Bradley, J.A. Cobble, I.L. Tregillis, K.A.D. Obrey, M.J. Schmitt, S.C. Hsu, R.C. Shah, N.S. Krasheninnikova, P. Hakel, S.H. Batha, R.J. Wallace, P. Fitzsimmons, A. Nikroo, P. McKenty Capsules driven with polar drive on the National Ignition Facility will be used to study mix in convergent geometry induced by an equatorial defect imposed on an inertial confinement fusion capsule. The 2.2-mm diameter capsules are mounted on a fill tube, through which a 5 atm deuterium fill is introduced. The inner 2 microns of the capsules will be doped with germanium to determine how much ablator material is mixed into the gas. Initial tests are scheduled for late July to verify the symmetry and performance of these capsules. Symmetry will be measured using backlit imaging from the equator and self-emission images from the pole. [Preview Abstract] |
Thursday, November 1, 2012 9:54AM - 10:06AM |
TO4.00003: Comparison of the Depth of Mix in ICF Capsules Driven with Symmetric or Polar Direct Drive on OMEGA J.A. Cobble, P.A. Bradley, S.C. Hsu, N.S. Krasheninnikova, T.J. Murphy, K.A.D. Obrey, M.J. Schmitt, R.C. Shah, I.L. Tregillis, S.H. Batha ICF capsules with an inner layer doped with titanium are imploded on the OMEGA laser facility with both 60-beam symmetric drive and 40-beam polar direct-drive (PDD) to determine the effect of PDD on the depth of mix into the ablator. The doped layer is either on the inside surface of the capsule or buried under up to 4.5 microns of plastic. The emission of the titanium is measured using an absolutely calibrated x-ray spectrometer. For spherical drive experiments, the titanium emission drops quickly with a burial depth of a few microns. Absorption of continuum emission from the imploded core by the titanium and the neutron yield of the implosions vary with the burial depth on a similar scale. PDD shots are currently scheduled and will determine if the amount of mixing is affected by the PDD, and if the emission scales with burial depth in the same way. [Preview Abstract] |
Thursday, November 1, 2012 10:06AM - 10:18AM |
TO4.00004: Comparing Simulated and Observed Spectroscopic Signatures of Mix in Omega Capsules I.L. Tregillis, R.C. Shah, P. Hakel, J.A. Cobble, T.J. Murphy, N.S. Krasheninnikova, S.C. Hsu, P.A. Bradley, M.J. Schmitt, S.H. Batha, R.C. Mancini The Defect-Induced Mix Experiment (DIME) campaign at Los Alamos National Laboratory uses multi-monochromatic X-ray imaging (MMI)\footnote{T. Nagayama, R.C. Mancini, R. Florido, et al, J. App. Phys. 109, 093303 (2011)} to detect the migration of high-Z spectroscopic dopants into the hot core of an imploded capsule. We have developed an MMI post-processing tool for producing synthetic datasets from two- and three-dimensional Lagrangian numerical simulations of Omega and NIF shots. These synthetic datasets are of sufficient quality, and contain sufficient physics, that they can be analyzed in the same manner as actual MMI data. We have carried out an extensive comparison between simulated and observed MMI data for a series of polar direct-drive shots carried out at the Omega laser facility in January, 2011. The capsule diameter was 870 microns; the 15 micron CH ablators contained a 2 micron Ti-doped layer along the inner edge. All capsules were driven with 17 kJ; some capsules were manufactured with an equatorial ``trench'' defect. This talk will focus on the construction of spectroscopic-quality synthetic MMI datasets from numerical simulations, and their correlation with MMI measurements. [Preview Abstract] |
Thursday, November 1, 2012 10:18AM - 10:30AM |
TO4.00005: Diagnosing the Extent of Mix in Omega Capsules Paul Bradley, James Cobble, Ian Tregillis, Tom Murphy, Mark Schmitt, Scott Hsu, Rahul Shah, Natalia Vinyard, Kim Obrey, James Fincke, Steve Batha We have investigated the role of turbulent mix in directly driven capsule implosions by modeling the February 2012 Defect Induced Mix Experiments on Omega with a two-dimensional Eulerian radiation-hydrodynamic code. The capsules had an outer diameter of 870 microns, were composed of 19 micron thick CH plastic ablators, and filled with 5 atm of deuterium gas. The capsules were imploded using 23 kJ laser energy in 1 ns flat-top pulses using 60 beams in symmetric drive. We use neutron yield and x-ray spectra from a Ti-doped layer buried at 0, 1.4, and 3.0 microns as mix diagnostics. The data show an increase in neutron yield and decrease in Ti line emission as the Ti-doped layer is buried at increasing depths away from the shell-gas interface. The Eulerian code results qualitatively mimic the neutron yield trend. We will also show how the simulated spectral emission compares to the data and discuss the implications for the extent of mix in ICF capsules. Work performed by Los Alamos National Laboratory under contract DE-AC52-06NA25396 for the National Nuclear Security Administration of the U.S. Department of Energy. [Preview Abstract] |
Thursday, November 1, 2012 10:30AM - 10:42AM |
TO4.00006: Symmetry tuning for DIME Campaign Natalia Krasheninnikova, Mark Schmitt, Ian Tregillis, P. Bradley, J. Cobble, G. Kyrala, T. Murphy, K. Obrey, S. Hsu, R. Shah, S. Batha, S. Craxton, P. McKenty Defect Induced Mix Experiment (DIME) investigates the effects of 4 pi as well as surface feature-driven mix on the directly driven ICF capsule implosion. To minimize the effects of the laser-drive asymmetry, beam pointings, pulse shape, and the energy distribution between the lasers need to be optimized for a particular capsule and shot energy. In support of the DIME experimental campaigns on OMEGA and NIF, symmetry tuning was performed with the rad-hydro code HYDRA. To assess the impact on the symmetry, synthetic radiographs and self-emission images were examined and compared with the experimental results from OMEGA and NIF shots. The dynamics of the capsules imploded under polar direct drive conditions were compared with symmetrically driven ones and the effects of cross-beam transfer and the laser imprinting on the symmetry were also investigated. Work performed by Los Alamos National Laboratory under contract DE-AC52-06NA25396 for the National Nuclear Security Administration of the U.S. Department of Energy. [Preview Abstract] |
Thursday, November 1, 2012 10:42AM - 10:54AM |
TO4.00007: Multiple Monochromatic Imaging of Implosions on the National Ignition Facility George A. Kyrala, T.J. Murphy, D. Martinson, F.E. Lopez, P. Polk, R.C. Shah, M.J. Schmitt, P.A. Bradley, J.A. Cobble, S.C. Hsu, K.A.D. Obrey, N.S. Krasheninnikova, M.J. Fagan, S.H. Batha, I. Tregillis, P. Fitzsimmons, A. Nikroo, R.J. Wallace Experiments are being planned to install and use a Multiple Monochromatic Imager at the National Ignition facility study mix in a convergent geometry inertial confinement fusion capsule. Initially, The 2.2-mm diameter capsules will be imploded using polar direct drive. The capsules are mounted on a fill tube, through which a 5 atm deuterium fill is introduced. The inner 2 microns of the 42-micron thick CH plastic walls of the capsules will be doped with germanium. When Ge mixes into the D2 plasma, H-like and He-like emission will be observed with the MMI, and a measure of the temporal and spatial distribution of the hot Germanium will be made Estimates of how much ablator material is mixed into the gas will be derived from the data. Initial tests are scheduled early August to qualify the instrument for later use on capsule with and without defects. [Preview Abstract] |
Thursday, November 1, 2012 10:54AM - 11:06AM |
TO4.00008: Multi-monochromatic imaging of defect-induced mix experiments at OMEGA Roberto Mancini, Heather Johns, Tirtha Joshi, Daniel Mayes, Tunay Durmaz, Taisuke Nagayama, Scott Hsu, Ian Tregillis, Natalia Krasheninnikova, James Cobble, Thomas Murphy, Rahul Shah, George Kyrala, Peter Hakel, Paul Bradley, Mark Schmitt In a series of polar-drive implosions performed at OMEGA for the defect-induced mix experiment (DIME) campaign of Los Alamos National Laboratory, two identical multi-monochromatic imager (MMI) instruments were fielded to record gated, x-ray spectrally-resolved images of D-filled Ti-doped plastic shells. The shells included a defect on the equatorial plane to study defect-induced mix while no-defect shells were employed in reference shots. The MMI data recorded simultaneously along quasi-orthogonal lines-of-sight afforded unique observations of the implosion based on the K-shell spectral signatures of the Ti tracer. Several analysis techniques have been used to process the MMI data (T. Nagayama et al, J. App. Phys. \textbf{109}, 093303 (2011)) in order to study defect-induced mixing by tracking the spatial distribution and state of the tracer. Comparisons were made with results from post-processed 2D and 3D simulations to provide further insight into the interpretation of the experimental results and to constrain the simulation physics model. [Preview Abstract] |
Thursday, November 1, 2012 11:06AM - 11:18AM |
TO4.00009: Analysis of simultaneous emission and absorption Ti spectral features observed with the MMI instrument in OMEGA implosions Tirtha Joshi, Heather Johns, Daniel Mayes, Tunay Durmaz, Roberto Mancini, Riccardo Tommasini, Jack Delettrez, Sean Regan, Taisuke Nagayama We discuss the observation and analysis of spectra from titanium-doped OMEGA direct-drive implosions. The targets were spherical plastic shells with a submicron Ti-doped tracer-layer initially located on the inner surface of the shell and filled with deuterium gas. The x-ray signal from the titanium tracer is observed at the collapse of the implosion and recorded with a streaked spectrometer (SSCA) and three identical gated,multi-monochromatic x-ray imager (MMI) instruments that view the implosion along three quasi-orthogonal lines-of-sight. Both streaked and MMI data show simultaneous emission and absorption features due to titanium K-shell line transitions but only the MMI data permits to diagnose the tracer's spatial properties in the core. To this end, MMI data were processed to obtain narrow-band images and spatially-resolved spectra.\footnote{T. Nagayama et al., J. App. Phys.109, 093303 (2011).} Abel inversion of angle-averaged image intensity profiles reveal the spatial distribution of the titanium tracer in the core, while detailed analysis of the space-resolved spectra yields temperature, density and mixing distributions. Results are presented for several shell thicknesses and implosions driven with different laser pulse shapes. [Preview Abstract] |
Thursday, November 1, 2012 11:18AM - 11:30AM |
TO4.00010: Hydrodynamic instabilities in sharp boundary approximation Snezhana I. Abarzhi For the first time, on the basis of conservation principles and thermodynamics laws, we derive the generalized Rankine-Hugoniot conditions that can be applied at unsteady and curved fronts. These conditions describe the dynamics of the front in an explicit and covariant form and can be applied in convergent or Cartesian system of coordinates. The theoretical framework is applied to the instabilities of Landau-Darrieus (LD), classical Rayleigh-Taylor (RT) and ablative Rayleigh-Taylor (ART). It is shown that in the case when if there is mass flow across the front and no acceleration presents (LD), the front is unstable only if three conditions are satisfied (1) bulk vorticity is generated; (2) energy flux across the front is imbalanced; (3) energy imbalance is large. When acceleration presents (RT and ART), the dependence is obtained of the instability growth-rate on the mass flow and energy imbalance across the front. Connection between the ablative RTI and classical RTI is made, and control parameters of the system are derived. The obtained results provide a theoretical framework for design of experiments in ICF-relevant conditions. [Preview Abstract] |
Thursday, November 1, 2012 11:30AM - 11:42AM |
TO4.00011: Scale coupling in Richtmyer-Meshkov flows induced by strong shocks R.F. Stellingwerf, M. Stanic, J.T. Cassibry, S.I. Abarzhi We report an integrated study of the Richtmyer-Meshkov (RM) flows under high energy density relevant conditions by means of smoothed particle hydrodynamics simulations and theoretical analysis. We show that significant amount of the shock energy goes into the compression and background of the fluids (that is supersonic), and only a small portion remains for interfacial mixing (that can be sub-sonic or supersonic). At late times, the RM bubbles flatten and decelerate, specific drag force decays quickly, the interfacial motion tends to be inertial, and the flow remains laminar rather than turbulent. At early times, shear-driven Kelvin-Helmholtz structures appear at the interface. At late times the velocity field is non-uniform and is characterized by intense dynamics in a vicinity of the front, effectively no motion in the bulk (rather than the background motion), and the checkerboard velocity patterns, which are induced by reverse cumulative jets. These jets appear in the fluid bulk and are accompanied by hot spots-local heterogeneous microstructures with temperature substantially higher than that in the ambient. Our results show that RMI dynamics is a multi-scale and heterogeneous process with a complicated character of scale coupling at the interface and in the bulk. [Preview Abstract] |
Thursday, November 1, 2012 11:42AM - 11:54AM |
TO4.00012: Numerical modeling and theoretical analysis of moderately and strongly nonlinear dynamics of the classical Richtmyer-Meshkov instability Marcus Herrmann, Alexander L. Velikovich, Snezhana I. Abarzhi There are many features of early- and late-time nonlinear RM instability growth that are not captured by simplified or ad hoc phenomenological models, such as Layzer's or drag-buoyancy. These include but are not limited to: late-time evolution of the bubble curvature; early-time acceleration of the spike; effect of finite values of ripple amplitude and Atwood number on early-time bubble and spike growth. We compare the results of numerical simulations with the predictions of the nonlinear theory, demonstrating a good agreement. The influences of viscosity, compressibility and the initial spectra on the nonlinear dynamics are outlined. [Preview Abstract] |
Thursday, November 1, 2012 11:54AM - 12:06PM |
TO4.00013: ABSTRACT WITHDRAWN |
Thursday, November 1, 2012 12:06PM - 12:18PM |
TO4.00014: Observed transition from Richtmyer-Meshkov jet formation through feedout oscillations to Rayleigh-Taylor instability in a laser target Y. Aglitskiy, M. Karasik, A.L. Velikovich, V. Serlin, J.L. Weaver, T.J. Kessler, A.J. Schmitt, S.P. Obenschain, S.P. Nikitin, N. Metzler, J. Oh Experimental study of hydrodynamic perturbation evolution triggered by a laser-driven shock wave breakout at the free rippled rear surface of a plastic target is reported. We observed a transition between two qualitatively distinct types of perturbation evolution: jet formation at low shock pressure and areal mass oscillations at high shock pressure, which correspond respectively to high and low values of effective adiabatic index. The experiments were done on the KrF Nike laser facility with laser wavelength 248 nm and a 4 ns pulse. We varied the number of beams overlapped on the plastic target to change the ablative pressure driving the shock wave through the target: 36 beams produce pressure of $\sim $8 Mbar, whereas a single beam irradiation reduces the pressure to $\sim $0.7 Mbar. With the help of side-on monochromatic x-ray imaging, planar jets manifesting the development of the Richtmyer-Meshkov-type instability in a non-accelerated target are observed at sub-megabar shock pressure. As the shock pressure exceeds 1 Mbar, instead of jet formation an oscillatory rippled expansion wave is observed, followed by the ``feedout'' of the rear-surface perturbations to the ablation front and the development of the Rayleigh-Taylor instability, which breaks up the accelerated target. [Preview Abstract] |
Thursday, November 1, 2012 12:18PM - 12:30PM |
TO4.00015: Thermal conductivity study at CH/Be interface by refraction-enhanced x-ray radiography Yuan Ping, Otto Landen, Jeff Koch, Damien Hicks, Russel Wallace, Gilbert Collins Transport properties near the fuel-ablator interface at the edge of an ICF capsule are important for modeling the growth of hydrodynamic instabilities, which determines the mix level in the fuel and is critical for successful ignition (Hammel, et al. HEDP 6, 671, 2010). A novel technique, time-resolved refraction-enhanced x-ray radiography, is developed to study thermal conductivity at the interface (Ping et al. J. Instru. 2011). Experiments using OMEGA laser have been carried out for CH/Be targets isochorically heated by x-rays to measure the evolution of the density gradient at the interface due to thermal conduction. The sensitivity of this radiographic technique to discontinuities enabled observation of shock/rarefraction waves propagating away from the interface. Comparison of data and simulation results using various conductivity models will be presented. [Preview Abstract] |
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