Bulletin of the American Physical Society
57th Annual Meeting of the APS Division of Plasma Physics
Volume 60, Number 19
Monday–Friday, November 16–20, 2015; Savannah, Georgia
Session GO5: Hydrodynamic Instability I |
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Chair: Paul Bradley, Los Alamos National Laboratory Room: 200 |
Tuesday, November 17, 2015 9:30AM - 9:42AM |
GO5.00001: Instability growth seeded by ablator material inhomogeneity in implosions on the National Ignition Facility S.W. Haan, S.H. Baxamusa, P.M. Celliers, G.W. Collins, D.S. Clark, A. Nikroo, M. Stadermann, D.D. Ho, N.B. Meezan, V. Smalyuk, C.R. Weber, H. Huang, D.E. Hoover, A.Q.L. Nguyen, W. Requieron, K.P. Youngblood, J.L. Kline, A.N. Simakov, D.C. Wilson, S.A. Yi Previous work [Physics of Plasmas 22, 032708 (2015)] on instability growth seeded by oxygen in CH NIF capsules has been extended. Oxygenation of CH can be caused by exposure to X-rays, UV, or visible light, such that irregularities in oxygen are very likely to dominate surface roughness as seed for instabilities in CH NIF implosions. 3D Rayleigh-Taylor experiments show structure that can most plausibly be explained as resulting from this oxygen. Experiments are planned on Omega and NIF to validate this phenomenon, which is still primarily simulation-motivated. Design work and available results for these experiments will be described. The oxygenation of CH might be mitigated by a coating of aluminum oxide on the outside of the shells. Growth is also seeded in Be shells, by density and composition non-uniformity from both oxygen and Ar, and in High Density Carbon shells by density nonuniformity. We present updated requirements for these nonuniformites, and compare to characterization of current shells. [Preview Abstract] |
Tuesday, November 17, 2015 9:42AM - 9:54AM |
GO5.00002: Modeling and diagnosing interface mix in layered ICF implosions C.R. Weber, L.F Berzak Hopkins, D.S. Clark, S.W. Haan, D.D. Ho, N.B. Meezan, J.L. Milovich, H.F. Robey, V.A. Smalyuk, C.A. Thomas Mixing at the fuel-ablator interface of an inertial confinement fusion (ICF) implosion can arise from an unfavorable in-flight Atwood number between the cryogenic DT fuel and the ablator. High-Z dopant is typically added to the ablator to control the Atwood number, but recent high-density carbon (HDC) capsules have been shot at the National Ignition Facility (NIF) without this added dopant. Highly resolved post-shot modeling of these implosions shows that there was significant mixing of ablator material into the dense DT fuel. This mix lowers the fuel density and results in less overall compression, helping to explain the measured ratio of down scattered-to-primary neutrons. Future experimental designs will seek to improve this issue through adding dopant and changing the x-ray spectra with a different hohlraum wall material. To test these changes, we are designing an experimental platform to look at the growth of this mixing layer. This technique uses side-on radiography to measure the spatial extent of an embedded high-Z tracer layer near the interface. [Preview Abstract] |
Tuesday, November 17, 2015 9:54AM - 10:06AM |
GO5.00003: Three-Dimensional Simulations of the Deceleration Phase of Inertial Fusion Implosions K.M. Woo, R. Betti, A. Bose, R. Epstein, J.A. Delettrez, K.S. Anderson, R. Yan, P.-Y. Chang, D. Jonathan, M. Charissis The three-dimensional radiation--hydrodynamics code \textit{DEC3D} has been developed to model the deceleration phase of direct-drive inertial confinement fusion implosions. The code uses the approximate Riemann solver on a moving mesh to achieve high resolution near discontinuities. The domain decomposition parallelization strategy is implemented to maintain high computation efficiency for the 3-D calculation through message passing interface. The implicit thermal diffusion is solved by the parallel successive-over-relaxation iteration. Results from 3-D simulations of low-mode Rayleigh--Taylor instability are presented and compared with 2-D results. A systematic comparison of yields, pressures, temperatures, and areal densities between 2-D and 3-D is carried out to determine the additional degradation in target performance caused by the three-dimensionality of the nonuniformities. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944 and DE-FC02-04ER54789 (Fusion Science Center). [Preview Abstract] |
Tuesday, November 17, 2015 10:06AM - 10:18AM |
GO5.00004: Effects of Long- and Intermediate-Wavelength Nonuniformities on Hot-Spot Energetics of Hydrodynamic Equivalent Targets A. Bose, R. Betti, K.M. Woo, A.R. Christopherson, D. Shvarts The impact of intermediate- and low-mode nonuniformities on the performance of inertial confinement fusion (ICF) implosions is investigated by a detailed study of hot-spot energetics. It is found that low- ($1 \sim 2$) and intermediate-mode ($1 \ge 10$) asymmetries affect the hot-spot hydrodynamics in very different ways. It is observed that for low-mode asymmetries, the fusion yield decreases because of a significant reduction in hot-spot pressure while the neutron-averaged hot-spot volume remains comparable to that of unperturbed (clean) simulations. On the other hand, implosions with moderate-amplitude, intermediate-wavelength modes, which are amplified by the Rayleigh--Taylor instability (RTI), exhibit a fusion-yield degradation primarily caused by a reduction in the burn volume without significant degradation of the pressure. For very large amplitudes, the intermediate modes show a ``secondary piston effect,'' where the converging RTI spikes compress a much smaller volume, allowing for a secondary conversion of the shell's kinetic energy to internal energy at a central region. Understanding the effects of nonuniformities on the hot-spot energetics provides valuable insight in determining the causes of performance degradation in current ICF experiments. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944 and DE-FC02-04ER54789 (Fusion Science Center). [Preview Abstract] |
Tuesday, November 17, 2015 10:18AM - 10:30AM |
GO5.00005: Numerical Simulations of Hydrodynamic Instability Growth in Polar-Direct-Drive Implosions at the National Ignition Facility A. Shvydky, M. Hohenberger, P.B. Radha, M.J. Rosenberg, R.S. Craxton, V.N. Goncharov, J.A. Marozas, F.J. Marshall, P.W. McKenty, S.P. Regan, T.C. Sangster Control of shell nonuniformities imprinted by the laser and amplified by hydrodynamic instabilities in the imploding target is critical to the success of polar-direct-drive ignition at the National Ignition Facility (NIF). To develop a platform for laser-imprint studies, hydrodynamic instability growth experiments in laser-driven implosions were performed on the NIF. The experiments used cone-in-shell targets with sinusoidal modulations of various wavelengths and amplitudes machined on the surface. Throughshell x-ray radiography was used to measure optical depth variations, from which the amplitudes of the shell areal-density modulations were extracted. Results of \textit{DRACO} simulations of the growth of preimposed modulations and imprint-seeded perturbations will be presented and compared with the experimental data. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. [Preview Abstract] |
Tuesday, November 17, 2015 10:30AM - 10:42AM |
GO5.00006: Three-Dimensional Single-Mode Nonlinear Ablative Rayleigh--Taylor Instability R. Yan, R. Betti, J. Sanz, B. Liu, A. Frank The nonlinear evolution of the ablative Rayleigh--Taylor (ART) instability is studied in three dimensions for conditions relevant to inertial confinement fusion targets. The simulations are performed using our newly developed code \textit{ART3D} and an astrophysical code \textit{AstroBEAR}. The laser ablation can suppress the growth of the short-wavelength modes in the linear phase but may enhance their growth in the nonlinear phase because of the vortex--acceleration mechanism.\footnote{ R. Betti and J. Sanz, Phys. Rev. Lett. \textbf{97}, 205002 (2006).} As the mode wavelength approaches the cutoff of the linear spectrum (short-wavelength modes), it is found that the bubble velocity grows faster than predicted in the classical 3-D theory. When compared to 2-D results, 3-D short-wavelength bubbles grow faster and do not reach saturation. The unbounded 3-D bubble acceleration is driven by the unbounded accumulation of vorticity inside the bubble. The vorticity is transferred by mass ablation from the Rayleigh--Taylor spikes into the ablated plasma filling the bubble volume. A density plateau is observed inside a nonlinear ART bubble and the plateau density is higher for shorter-wavelength modes. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. [Preview Abstract] |
Tuesday, November 17, 2015 10:42AM - 10:54AM |
GO5.00007: Qualitative and quantitative features of Rayleigh-Taylor mixing dynamics Praveen Ramaprabhu, Varad Karkhanis, Andrew Lawrie, Aklant Bhowmick, Snezhana Abarzhi We consider dynamics of Rayleigh-Taylor (RT) flow in a large aspect ratio three-dimensional domain with square symmetry in the plane for fluids with contrasting densities. In order to quantify the interface evolution from a small amplitude single-mode initial perturbation to advanced stage of RT mixing, we apply numerical simulations using the MOBILE code, theoretical analyses, including group theory and momentum model, as well as parameters describing the interplay between acceleration and turbulence. We find: In RT flow, the fluid motion is intense near the interface and is negligible far from the interface. At late times the growth rates of RT bubbles and spikes may increase without a corresponding increase of length-scales in the direction normal to acceleration. The parameters describing the interplay between acceleration and turbulence in RT mixing are shown to scale well with the flow Reynolds number and Froude number. [Preview Abstract] |
Tuesday, November 17, 2015 10:54AM - 11:06AM |
GO5.00008: Bell-Plesset effects in Rayleigh-Taylor instability of finite-thickness spherical and cylindrical shells A.L. Velikovich, P.F. Schmit Bell-Plesset effects accounting for the time dependence of the radius, velocity and acceleration of the Rayleigh-Taylor-unstable surface are ubiquitous in the instability of spherical laser targets and magnetically driven cylindrical liners. We present an analytical model that, for an ideal incompressible fluid and small perturbation amplitudes, exactly accounts for the Bell-Plesset effects in finite-thickness targets and liners through acceleration and deceleration phases. We derive the time-dependent dispersion equations determining the ``instantaneous growth rate'' and demonstrate that by integrating this growth rate over time (the WKB approximation) we accurately evaluate the number of perturbation e-foldings during the acceleration phase. In the limit of the small target/liner thickness, we obtain the exact thin-shell perturbation equations and approximate thin-shell dispersion relations, generalizing the earlier results of Harris (1962), Ott (1972) and Bud'ko et al. (1989). This research was supported by the US DOE/NNSA (A.L.V.), and in part by appointment to the Sandia National Laboratories Truman Fellowship in National Security Science and Engineering (P.F.S.), which is part of the Laboratory Directed Research and Development (LDRD) Program, Project No. 165746, and sponsored by Sandia Corporation (a wholly owned subsidiary of Lockheed Martin Corporation) as Operator of Sandia National Laboratories under its U.S. Department of Energy Contract No. DE-AC04-94AL85000. [Preview Abstract] |
Tuesday, November 17, 2015 11:06AM - 11:18AM |
GO5.00009: Richtmyer-Meshkov jet formation from rear target ripples in plastic and plastic/aluminum laser targets Y. Aglitskiy, A.L. Velikovich, M. Karasik, V. Serlin, J.L. Weaver, A.J. Schmitt, S.P. Obenschain We report experimental observations of jets produced from the rear surface of laser targets after a passage of the laser-driven shock wave. As in our previous work, Aglitskiy et al., Phys. Plasmas (2012), the jets are produced via the shaped-charge mechanism, a manifestation of a Richtmyer-Meshkov instability for a particular case of the Atwood number A$=$-1. The experiments done on the KrF Nike laser facility with laser wavelength 248 nm, a 4 ns pulse, and low-energy drive regime that used only 1 to 3 overlapping Nike beams and generated ablative pressure below 1 Mbar. Our 50 um thick planar targets were rippled on the rear side with wavelength 45 $\mu$m and peak-to-valley amplitude 15 $\mu$m. The targets were made either of solid plastic or of aluminum with a 10 $\mu$m thick plastic ablator attached to avoid the radiation preheat. The jets were extremely well collimated, which made possible our side-on observations with monochromatic x-ray imaging. We saw a regular set of jets, clearly separated along the 500 $\mu$m line of sight. Aluminum jets were found to be slightly better collimated than plastic jets. A quasi-spherical late-time expansion of Al jets starting from the tips has not been previously seen in experiments or simulations. [Preview Abstract] |
Tuesday, November 17, 2015 11:18AM - 11:30AM |
GO5.00010: Effect of initial perturbation amplitude on Richtmyer-Meshkov flows induced by strong shocks Zachary Dell, Robert Stellingwerf, Snezhana Abarzhi We study the effect initial perturbation on the Richtmyer-Meshkov (RM) flows induced by strong shocks in fluids with contrasting densities. Smooth Particle Hydrodynamics simulations are employed. Broad range of shock strengths and density ratios is considered (Mach=3,5,10, and Atwood=0.6,0.8,0.95). The amplitude of initial single mode sinusoidal perturbation of the interface varies from 0\% to 100\% of its wavelength. We analyze the initial growth-rate of the RMI immediately after the shock passage, when the perturbation amplitude increases linearly with time. We find that the initial growth-rate of RMI is a non-monotone function of the amplitude of the initial perturbation. This restrains the amount of energy that can be deposited by the shock at the interface. The maximum value of the initial growth-rate depends strongly and the corresponding value of the initial perturbation amplitude depends only slightly on the shock strength and density ratio. The maximum value of the initial growth-rate increases with the increase of the Atwood number for a fixed Mach number, and decreases with the increase of the Mach number for a fixed Atwood number. We argue that the non-monotonicity of RMI growth-rate is a result of a combination of geometric effect and the effect of secondary shocks. [Preview Abstract] |
Tuesday, November 17, 2015 11:30AM - 11:42AM |
GO5.00011: Effect of pressure field fluctuations on the nonlinear evolution of Richtmyer-Meshkov coherent structure Aklant Bhowmick, Snezhana Abarzhi We consider the effect of pressure fluctuations on the evolution of Richtmyer-Meshkov (RM) flows. The pressure fluctuations are induced by non-uniformities in the fluid bulk and are modeled as a time dependent acceleration with the power-law exponent (-2). We consider a large scale periodic coherent structure of bubbles and spikes in a two-dimensional RM flow, and obtain asymptotic solutions describing nonlinear dynamics of the structure using group theory analysis. We show that regular asymptotic solutions describing the bubble dynamics form a one-dimensional family. The family can be parameterized by the curvature of the bubble front. The stability of the family solutions is analyzed. The physically significant solution in the family is interpreted as the stable solution with the maximum velocity. The associated flow fields in the vicinity of the bubble tip indicate the formation of vortices and the presence of shear at the interface, which may lead to cascading of energy of smaller scales. The fluids move intensively near the interface, and there is effectively no motion away from the interface. Dependence of the asymptotic dynamics to pressure fluctuations is studied both qualitatively and quantitatively, including the limiting cases of strong and weak fluctuations. [Preview Abstract] |
Tuesday, November 17, 2015 11:42AM - 11:54AM |
GO5.00012: Influence of interference of perturbation waves on the dynamics of Richtmyer-Meshkov flows Arun Pandian, Snezhana Abarzhi We study the dynamics of structures that are formed due to Richtmyer-Meshkov instability (RMI) at the interface between two fluids with different densities when a strong shock wave refracts it [1]. While previous research in this area was focused on the effects of the wavelength and amplitude of the interface perturbation, the information was largely ignored on the influences of the relative phase of a multi-wave perturbation and the interference of the perturbation waves on RMI evolution. Applying group theory analysis and Smooth Particle Hydrodynamics simulations, we study the effects of the relative phase of the interfacial sinusoidal waves on the structure of bubbles and spikes that is formed at the interface after the shock passage. A number of new qualitative and quantitative effects are found, and the effect of the wave interference on RMI evolution is observed. In particular, evidences so far indicate that the symmetry of the interface strongly influences the spike morphology as compared to asymmetric cases. We discuss how one may control the growth of RMI by controlling the phases of waves of the initial perturbation. [Preview Abstract] |
Tuesday, November 17, 2015 11:54AM - 12:06PM |
GO5.00013: Measurements of Reduced Hydrodynamic Instability Growth in Adiabat Shaped Implosions at the NIF Daniel Casey, Andrew MacPhee, Jose Milovich, Vladimir Smalyuk, Dan Clark, Harry Robey, Luc Peterson, Kevin Baker, Chris Weber Hydrodynamic instabilities can cause capsule defects and other perturbations to grow and degrade implosion performance in ignition experiments at the National Ignition Facility (NIF). Radiographic measurements of ablation front perturbation growth were performed using adiabat-shaped drives which are shown to have lower ablation front growth than the low foot drive. This is partly due to faster Richtmyer-Meshkov (RM) oscillations during the shock transit phase of the implosion moving the node in the growth factor spectrum to lower mode numbers reducing the peak growth amplitude. This is demonstrated experimentally by a reversal of the perturbation phase at higher mode numbers (120-160). These results show that the ablation front growth and fuel adiabat can be controlled somewhat-independently and are providing insight into new, more stable, ignition designs. [Preview Abstract] |
Tuesday, November 17, 2015 12:06PM - 12:18PM |
GO5.00014: Comparison of hydrodynamic simulations with two-shockwave drive target experiments Varad Karkhanis, Praveen Ramaprabhu, William Buttler We consider hydrodynamic continuum simulations to mimic ejecta generation in two-shockwave target experiments [1], where metallic surface is loaded by two successive shock waves. Time of second shock in simulations is determined to match experimental amplitudes at the arrival of the second shock. The negative Atwood number ($A \to -1$) of ejecta simulations leads to two successive phase inversions of the interface corresponding to the passage of the shocks from heavy to light media in each instance. Metallic phase of ejecta (solid/liquid) depends on shock loading pressure in the experiment, and we find that hydrodynamic simulations quantify the liquid phase ejecta physics with a fair degree of accuracy, where RM instability is not suppressed by the strength effect. In particular, we find that our results of free surface velocity, maximum ejecta velocity, and maximum ejecta areal density are in excellent agreement with their experimental counterparts, as well as ejecta models [2,3]. We also comment on the parametric space for hydrodynamic simulations in which they can be used to compare with the target experiments. \\[4pt] [1] W. T. Buttler et al., J. Appl. Phys., 116 (2014). \\[0pt] [2] Guy Dimonte et al., J. Appl. Phys., 113 (2013). \\[0pt] [3] W. T. Buttler et al., J. Fluid Mech., 703 (2012). [Preview Abstract] |
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