Bulletin of the American Physical Society
50th Annual Meeting of the Division of Plasma Physics
Volume 53, Number 14
Monday–Friday, November 17–21, 2008; Dallas, Texas
Session CO5: Hydrodynamic Instability |
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Chair: Valeri Goncharov, University of Rochester Room: Reunion C |
Monday, November 17, 2008 2:00PM - 2:12PM |
CO5.00001: Investigation of the Effects of Target Mounting in Direct-Drive Implosions on OMEGA I.V. Igumenshchev, F.J. Marshall, J.A. Marozas, V.A. Smalyuk, R. Epstein, T.J.B. Collins, V.N. Goncharov, T.C. Sangster Target mounting can affect the performance of direct-drive-implosion experiments on OMEGA by introducing hydrodynamic perturbations and perturbations caused by the laser-light shadowing and refraction. Two target-mounting types currently employed on OMEGA, stalks (that use glue) and C-mounts (that use four spider silks and glue), have been considered. We investigate the effects of stalks, glue spots, and spider silks in planar experiments and model these experiments using the 2-D radiation hydrodynamic code \textit{DRACO}. Detailed 2-D implosion simulations of OMEGA's warm and cryogenic targets, including the effects of stalks, glue spots, and spider silks, will be presented. This work was supported by U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC52-08NA28302. [Preview Abstract] |
Monday, November 17, 2008 2:12PM - 2:24PM |
CO5.00002: 3-D Modeling of Planar Target-Mount Perturbation Experiments on OMEGA T.J.B. Collins, F.J. Marshall, J.A. Marozas, M.J. Bonino, R. Forties, V.N. Goncharov, I.V. Igumenshchev, P.W. McKenty, V.A. Smalyuk OMEGA cryogenic targets are suspended in the target chamber using four spider silks attached to a C-shaped mount. The spider silks are typically composed of two entwined protein strands comparable to 1 \textit{$\mu $}m in diameter. The silks and mount refract the incident laser light and cast shadows on the target surface. Experiments to measure the effects of the silks on target illumination have been performed in planar geometry using silks suspended parallel to a 20-\textit{$\mu $}m-thick laser-driven target. The evolution of the surface perturbations introduced by the silks was measured using x-ray backlighting. The results of these experiments will be compared to simulations performed with \textit{DRACO}, employing three-dimensional (3-D) planar hydrodynamics and a new 3-D refractive ray-trace package written specifically for this geometry. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC52-08NA28302. [Preview Abstract] |
Monday, November 17, 2008 2:24PM - 2:36PM |
CO5.00003: Rayleigh--Taylor Measurements in Planar Cryogenic D$_{2}$ Targets Using X-Ray Radiography on OMEGA J.D. Hager, V.A. Smalyuk, S.X. Hu, D.D. Meyerhofer, T.C. Sangster Understanding how areal-density modulations grow in cryogenic D$_{2}$ at ablative Rayleigh--Taylor unstable interfaces is crucial to achieving ignition in direct-drive inertial confinement fusion. Experiments were preformed on OMEGA where planar cryogenic targets, consisting of 50 \textit{$\mu $}m of D$_{2}$ in between two 5-\textit{$\mu $}m CD windows, were driven with square and shaped laser pulses. Initial modulations consisted of 2-D preimposed and 3-D imprinted perturbations. Once the foot of the drive ablates the front CD window, the modulations grow in the D$_{2}$ during the main part of the pulse. These modulations feed through to the rear surface as they grow, where they can be detected with face-on, x-ray radiography using an $\sim$1.3-keV uranium backlighter. Temporal growth of these modulations and results of 2-D simulations will be presented. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement DE-FC52-08NA28302. [Preview Abstract] |
Monday, November 17, 2008 2:36PM - 2:48PM |
CO5.00004: Time evolution of self-generated electromagnetic fields around imploding ICF capsules F.H. Seguin, C.K. Li, M. Manuel, J.R. Rygg, J.A. Frenje, N. Sinenian, D. Casey, R.D. Petrasso, R. Betti, O.V. Gotchev, J.P. Knauer, F.J. Marshall, D.D. Meyerhofer, T.C. Sangster, V.A. Smalyuk The behavior of electromagnetic fields generated by laser-plasma interactions during the direct-drive implosion of ICF capsules has been studied with time-gated, monoenergetic-charged-particle radiography at the OMEGA laser facility. Images with complementary information were recorded simultaneously with 15-MeV protons, 3-MeV protons, and 3.6-MeV alpha particles. Details of the time evolution of the fields' spatial structures and magnitudes and their possible connections with specific hydrodynamic and/or laser-plasma-interaction instabilities will be discussed. This work was performed in part at the LLE National Laser User's Facility (NLUF), and was supported in part by US DOE, LLNL, LLE and the Fusion Science Center at Univ. Rochester. *Currently at LLNL. [Preview Abstract] |
Monday, November 17, 2008 2:48PM - 3:00PM |
CO5.00005: Studies of self-generated electric fields in imploding capsules: Candidate origins and impact on stability P.A. Amendt, S.C. Wilks, C.K. Li, R.D. Petrasso, F.H. Seguin The generation of strong, self-generated electric fields (10$^{8}$-10$^{9}$ V/m) in direct-drive, inertial-confinement-fusion capsules was recently reported [1]. Various models are considered to explain the observed electric field evolution, including the potential roles of electron pressure gradients, shocks and acceleration-induced charge-separations on the fuel-pusher interface. A linear, compressible, perturbation analysis based on velocity potentials is adapted to include the presence of plasma electric fields and is shown to lead to super-classical Rayleigh-Taylor growth driven by an ionization imbalance across the fuel-pusher interface. The enhanced Rayleigh-Taylor growth is shown to be significant for low Atwood-number, low-\textit{Z} shells as in the CH ablator of an Omega-scale HEP5 [2] implosion target. [1] J.R. Rygg \textit{et al}., Science 319, 1223 (2008); C.K. Li \textit{et al}., PRL 100, 225001 (2008). [2] P.A. Amendt, R.E. Turner and O.L. Landen, PRL 89, 165. [Preview Abstract] |
Monday, November 17, 2008 3:00PM - 3:12PM |
CO5.00006: Experimental tests of Rayleigh-Taylor stabilization mechanisms with long pulse gas-filled halfraums on OMEGA A. Casner, G. Huser, M. Vandenboomgaerde, S. Liberatore, L. Masse, D. Galmiche Mitigation of Rayleigh-Taylor instabilities growth is a key issue on the road toward ignition. The graded doped ablator is a common concept for NIF [1] and LMJ [2] point designs. A complementary stabilization mechanism based on anisotropic thermal diffusion was theoretically underlined [3] for the ablative Rayleigh-Taylor instability. We will present the first ever experimental tests of these mechanisms. Indirect drive experiments were performed on the OMEGA laser facility with a long-pulse platform. We used in fact gas-filled halfraums and stack 15 drive beams along 2 cones to create a 7 ns long radiation drive. Halfraum energetics with E-IDI-300 phase plates was validated by dedicated shots along P5/P8 and is fairly reproduced by the simulations. These drive measurements allowed also to determine the graded doped planar emulator whose layers thicknesses and composition should be carefully optimized . Side-on and face-on data acquired with germanium-doped plastic samples (modulations wavelength 35 and 50 microns) will be presented and compared with FCI2 hydrocodes simulations. [1] S.W. Haan \textit{et al.}, Phys. Plasmas \textbf{12}, 056316 (2005). [2] C C-Cl\'{e}rouin \textit{et al} 2008 \textit{J. Phys.: Conf. Ser.} \textbf{112} 022023 [3] L. Masse$.$, Phys. Rev. Lett. 98, 245001 (2007). [Preview Abstract] |
Monday, November 17, 2008 3:12PM - 3:24PM |
CO5.00007: Small-Amplitude Richtmyer-Meshkov Instability at a Re-Shocked Material Interface A.L. Velikovich, S.T. Zalesak, N. Metzler, Y. Aglitskiy We report an exact small-amplitude theory of the Richtmyer-Meshkov (RM) instability developing at a re-shocked material interface and favorably compare it to our simulations. The re-shock is seen to restart the classical RM instability growth from a larger initial amplitude, at a higher rate, and change its direction from heavy-to-light to light-to heavy and vice versa. Similarly, if a Rayleigh-Taylor (RT) unstable interface is strongly re-shocked from either the heavy or light fluid side, the fast RM growth is triggered. If a RT-unstable ablation front is re-shocked, it exhibits the ablative RM-instability, that is, low-frequency decaying oscillations [V. N. Goncharov, PRL \textbf{82}, 2091 (1998); Y. Aglitskiy \textit{et al}., PRL \textbf{87}, 265001 (2001)]. This is predicted for colliding foil experiments on the Nike laser, where a RT-unstable ablation front is re-shocked by the strong shock wave produced in the collision of the laser-driven plastic foil with a stationary foam layer. The re-shock stops the acceleration and switches the perturbation evolution from the ablative RT to the ablative RM regime. [Preview Abstract] |
Monday, November 17, 2008 3:24PM - 3:36PM |
CO5.00008: Ablative Rayleigh-Taylor and Richtmyer-Meshkov Instabilities in Laser-Accelerated Colliding Foils Y. Aglitskiy, N. Metzler, M. Karasik, V. Serlin, J. Weaver, S.P. Obenschain, J. Oh, A.J. Schmitt, A.L. Velikovich, S.T. Zalesak, J.H. Gardner, E.C. Harding In our experiments done on the Nike KrF laser, we study instability growth at shock-decelerated interfaces in planar colliding-foil experiments. We use streaked monochromatic (1.86 keV) x-ray face-on imaging diagnostics to measure the areal mass modulation growth caused by the instability. Higher x-ray energies up to 5.25 keV are used to follow the shock propagation as well as the 1D dynamics of the collision. While a laser-driven foil is accelerated towards the stationary low-density foam layer, an ablative RT instability develops. Having reached a high velocity, the foil hits the foam layer. The impact generates strong shocks in the plastic and in the foam. The reflected shock wave re-shocks the ablation front, its acceleration stops, and so does the observed RT growth. This is followed by areal mass oscillations due to the ablative RM instability and feedout mechanisms, of which the latter dominates. [Preview Abstract] |
Monday, November 17, 2008 3:36PM - 3:48PM |
CO5.00009: Reduction of ablative Richtmyer-Meshkov growth on planar CH targets with a high-Z overcoat Max Karasik, J.L. Weaver, V. Serlin, J.W. Bates, A.L. Velikovich, Y. Aglitskiy Thin (400-800\AA) high-Z overcoat on the laser side of the target can be effective in suppressing laser imprint [S.\ P.\ Obenschain et al.\ Phys.\ Plasmas 9, 2234 (2002)]. The present experiments investigate the effect of the coating on instability seeding by target imperfections. Evolution of a pre-imposed ripple is observed by face-on x-ray radiography using Bragg reflection from a curved crystal coupled to an x-ray streak camera. X-ray flux from the high-Z overcoat is monitored using absolutely calibrated time-resolved x-ray spectrometers. The overcoat is found to change the ablative Richtmyer-Meshkov (RM) stage of the ripple evolution, which forms the seed for the subsequent RT growth, due to the initial x-ray ablation with the high-Z overcoat. The measurements show a significant reduction in the ripple amplitude growth due to the ablative RM for overcoated targets, resulting in lower initial amplitudes for RT growth. This work is supported by US DOE/NNSA. [Preview Abstract] |
Monday, November 17, 2008 3:48PM - 4:00PM |
CO5.00010: Supersonic shear flows in laser driven high-energy-density plasmas created by the Nike laser E.C. Harding, R.P. Drake, R.S. Gillespie, M.J. Grosskopf, J.R. Ditmar, Y. Aglitskiy, J.L. Weaver, A.L. Velikovich, T. Plewa In high-energy-density (HED) plasmas the Kelvin-Helmholtz (KH) instability plays an important role in the evolution of Rayleigh-Taylor (RT) and Richtmyer-Meshkov (RM) unstable interfaces, as well as material interfaces that experience the passage one or multiple oblique shocks. Despite the potentially important role of the KH instability few experiments have been carried out to explore its behavior in the high-energy-density regime. We report on the evolution of a supersonic shear flow that is generated by the release of a high velocity ($>$100 km/s) aluminum plasma onto a CRF foam ($\rho $ = 0.1 g/cc) surface. In order to seed the Kelvin-Helmholtz (KH) instability various two-dimensional sinusoidal perturbations ($\lambda $ = 100, 200, and 300 $\mu $m with peak-to-valley amplitudes of 10, 20, and 30 $\mu $m respectively) have been machined into the foam surface. This experiment was performed using the Nike laser at the Naval Research Laboratory. [Preview Abstract] |
Monday, November 17, 2008 4:00PM - 4:12PM |
CO5.00011: ABSTRACT WITHDRAWN |
Monday, November 17, 2008 4:12PM - 4:24PM |
CO5.00012: Observation and Simulation of Electro-thermal Instabilities in Condensed States of Aluminum and Copper Kyle Peterson, Daniel Sinars, Mark Herrmann, Edmund Yu Electro-thermal instabilities, also referred to as overheat instabilities, are the result of non-uniform heating due to temperature dependence in the conductivity of a material. In the condensed state of metals, the conductivity decreases with increasing temperature, which can result in axial layered instabilities perpendicular to current flow. These instabilities were studied on the Sandia National Laboratories Z facility by driving solid, 6mm and 12mm diameter, aluminum and copper rods with a $\sim$ 100 ns risetime current pulse to surface current densities of $\sim 10^{8} A/cm^{2}$. Simulations of these experiments were performed with LASNEX, a 2D magnetohydrodyanamic code. We present the data and analysis of these experiments including a comparison of the electro-thermal instability growth rate and striation wavelength measured using two frame x-ray backlighting to simulated radiographs. [Preview Abstract] |
Monday, November 17, 2008 4:24PM - 4:36PM |
CO5.00013: Analytical theory for the interaction of a planar shock wave with isotropic turbulence Juan Gustavo Wouchuk, Cesar Huete Ruiz de Lira, Alexander Velikovich An analytical model is presented to describe the interaction of a planar incident shock wave with a 3D field of vorticity perturbations, a problem of fundamental importance which attracts the attention of the scientific community for more than fifty years [1]. Assuming isotropy of the perturbations in the fluid ahead of the shock front, the mode averaging can be performed analytically. Fully closed analytical expressions for the turbulent kinetic energy amplification factor and the intensity of sound emitted by the shock wave derived for the whole range of shock intensities and gas gammas are presented for the first time. Excellent agreement with existing simulations and experiments [1] is demonstrated. [1] M. J. Lighthill, Proc. Roy. Soc. London A 198, 554 (1949); H. S. Ribner, AIAA J. 25, 436 (1987), J. Fluid Mech. 35, 289 (1969); S. Lee et al. J. Fluid Mech. 340, 225 (1997); G. Dimonte and R. Tipton, Phys. Fluids 18, 85101 (2006). [Preview Abstract] |
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