Bulletin of the American Physical Society
55th Annual Meeting of the APS Division of Plasma Physics
Volume 58, Number 16
Monday–Friday, November 11–15, 2013; Denver, Colorado
Session YO4: ICF Hydrodynamic Stability |
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Chair: Pravesh Patel, Lawrence Livermore National Laboratory Room: Plaza D |
Friday, November 15, 2013 9:30AM - 9:42AM |
YO4.00001: Observations of the Ablative Richtmyer-Meshkov Effect Relevant to Indirect-Drive Inertial Confinement Fusion Eric Loomis, Dave Braun, Steve Batha, Otto Landen Recent simulations and experiments have shown that isolated features on the outer surface of Inertial Confinement Fusion (ICF) ignition capsules can profoundly impact capsule performance by leading to material jetting or mixing into the hotspot. Controlling the growth of these artifacts is complicated due to uncertainties in equation of state (EOS) models used in simulation codes. Here we report on measurements pertaining to the growth and decay of isolated defects due to x-ray ablation Richtmyer-Meshkov in CH capsules in order to validate these models. Face-on transmission radiography was used to measure the evolution of Gaussian bump arrays in plastic targets. Au halfraums heated to radiation temperatures near 70 eV using 15 beams in a 7.5 ns pulse from the Omega laser (Laboratory for Laser Energetics, University of Rochester, NY) indirectly drove the samples while simultaneous radiographs from Ta and Y backlighter foils were recorded. Shock speed measurements were also made with Omega's Active Shock Break Out (ASBO) diagnostic in conjunction with the x-ray flux recorded by a soft x-ray power diagnostic (DANTE) were used to determine drive conditions in the target. Measurements of 5 micron tall, 17 micron wide bumps show a decrease in bump areal density between 4.5 and 7.5 ns while 33 micron wide bumps saturate near 3 ns consistent with LEOS 5310 and SESAME 7592 simulations. [Preview Abstract] |
Friday, November 15, 2013 9:42AM - 9:54AM |
YO4.00002: Alternate Ablator Concepts for High-Foot NIF Ignition Capsules Thomas Dittrich, Omar Hurricane, Shon Prisbrey Encouraging results have been obtained using a strong first shock during the implosion of carbon-based ablator ignition capsules. This strong first shock is launched by an 80 eV to 100 eV ``foot'' in the x-ray drive pulse in a set of experiments referred to as the ``high-foot'' series. This higher temperature foot has several advantages to capsule performance, including reduced sensitivity to ablator opacity modeling and significant improvement in capsule implosion stability. Other ablator materials such as Be and B4C may have advantages over carbon-based materials such as CH (GDP) and HDC (high-density carbon). Performance of these alternate ablator materials will be presented. [Preview Abstract] |
Friday, November 15, 2013 9:54AM - 10:06AM |
YO4.00003: Mitigation of laser imprinting with diamond ablator for direct-drive inertial confinement fusion targets Keisuke Shigemori, Hiroki Kato, Mitsuo Nakai, Yoichiro Hironaka, Tatsuhiro Sakaiya, Hideo Nagatomo, Atsushi Sunahara, Shinsuke Fujioka, Hiroshi Azechi, Katsuya Shimizu Diamond is very hard material, and uncompressible under its elastic limit ($\sim$ 180 GPa), which means that diamond has a very large effective specific heat ratio. Since the imprint efficiency is a function of the specific heat of the target material, diamond is a promising candidate for the ablator material. We carried out an experiment to measure the target imprinting on diamond foils. The thickness of the diamond foils were 8-15 $\mu $m. We also irradiated polystyrene foils as a reference in order to compare the imprint level. The intensity modulation was imposed for the foot pulse with the wavelength on the target of $\sim$ 100 $\mu $ m. The intensity of the foot pulse was $\sim$ 5 x 10$^{12}$ W/cm$^{2}$ followed by the main pulse ($\sim$ 1 x 10$^{14}$ W/cm$^{2})$ to accelerate the foil. Areal density perturbation was measured with face-on backlighting technique. The imprint amplitude was evaluated by measuring areal density perturbation which is amplified by Rayleigh-Taylor instability while the target is accelerated after the target imprinting with a foot pulse. [Preview Abstract] |
Friday, November 15, 2013 10:06AM - 10:18AM |
YO4.00004: Mitigation of Electrothermal Instabilities with Thick Insulating Coatings Kyle Peterson, Thomas Awe, Edmund Yu, Daniel Sinars, Michael Cuneo We will show results of recent experiments on Sandia's Z facility that demonstrate a dramatic reduction in instability growth when thick insulating coatings are used to mitigate electrothermal instability growth [1,2] in magnetically driven imploding liners. These results also provide further evidence that the inherent surface roughness as a result of target fabrication is not the dominant seed for the growth of Magneto-Rayleigh-Taylor (MRT) instabilities in liners with carefully machined smooth surfaces ($\sim$100 nm surface RMS or better), but rather electrothermal instabilities that form early in the electrical current pulse as Joule heating melts and vaporizes the liner surface. More importantly, these results suggest a mechanism for possibly reducing the integral MRT instability growth substantially in magnetically driven inertial confinement fusion concepts such as MagLIF [3].\\[4pt] [1] K.J. Peterson et al., Phys. Plasmas 19, 092701 (2012)\\[0pt] [2] K.J. Peterson et al., Phys. Plasmas 20, 056305 (2013)\\[0pt] [3] S.A. Slutz et al., Phys. Plasmas 17, 056303 (2010) [Preview Abstract] |
Friday, November 15, 2013 10:18AM - 10:30AM |
YO4.00005: Laser Imprint Suppression for Spike Pulseshapes using a Thin High-Z Overcoat Max Karasik, Y. Aglitskiy, J. Oh, J.L. Weaver, J.W. Bates, V. Serlin, S.P. Obenschain In directly driven ICF, most of the laser imprint is expected to occur during the initial part of the laser pulse, which generates the first shocks necessary to compress the target to achieve high gain. Previous experiments where the laser pulse had a low intensity foot to generate the first shock found that a thin ($ < 1000${\AA}) high-Z overcoat is effective in suppressing imprint[PoP 9, 2234 (2002)]. The overcoat initially absorbs the laser and emits soft x-rays that ablate the target, allowing a large stand-off distance between laser absorption and ablation and giving higher ablation velocity. The coating is thin so that it becomes transparent to the main part of the pulse, minimizing x-ray preheat. The present experiments aim to extend this method to spike pulseshapes used in current target designs, with a view to direct drive on the NIF. Measurements of RT-amplified areal mass non-uniformity on planar targets driven by ISI-smoothed Nike KrF laser are made by curved crystal x-ray radiography. X-ray flux from the high-Z layer is monitored using absolutely calibrated time-resolved x-ray spectrometers. Simultaneous side-on radiography allows observation of the layer dynamics as well as target trajectory. The effect on imprint as well as pre-imposed ripple growth will be presented. [Preview Abstract] |
Friday, November 15, 2013 10:30AM - 10:42AM |
YO4.00006: Two-Dimensional Numerical Evaluation of 1-D Multi-FM SSD Experiments on OMEGA EP A. Shvydky, M. Hohenberger, J.A. Marozas, M.J. Bonino, D. Canning, T.J.B. Collins, T.J. Kessler, B.E. Kruschwitz, P.W. McKenty, D.D. Meyerhofer, T.C. Sangster, J.D. Zuegel Adequate single-beam smoothing is crucial for successful direct-drive target implosions. One-dimensional, multi-FM smoothing by spectral dispersion (SSD) has been proposed to provide the required level of smoothing.\footnote{J. A. Marozas, J. D. Zuegel, and T. J. B. Collins, Bull. Am. Phys. Soc. \textbf{55}, 294 (2010).} A prototype multi-FM SSD system has been integrated into one beamline of the OMEGA EP Laser System and has been used in laser-driven planar-foil experiments to study the effectiveness of multi-FM SSD in reducing laser imprint. Recent experiments have achieved significantly improved signal-to-noise by employing a newly-qualified soft x-ray imaging diagnostic. Results of 2-D \textit{DRACO} simulations will be compared with the available experimental data. The simulations include realistic time-dependent far-field spot intensity calculations that emulate the effect of the SSD and have a sufficiently fine computational mesh to resolve speckles. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. [Preview Abstract] |
Friday, November 15, 2013 10:42AM - 10:54AM |
YO4.00007: Measurement of 1-D Multi-FM SSD Smoothing Performance on OMEGA EP M. Hohenberger, A. Shvydky, J.A. Marozas, T.J.B. Collins, G. Fiksel, T.J. Kessler, P.W. McKenty, D.D. Meyerhofer, J.D. Zuegel, T.C. Sangster Polar-drive ignition on the National Ignition Facility (NIF) requires single-beam smoothing to minimize imprinting of laser nonuniformities that can negatively affect implosion performance. One-dimensional multi-FM smoothing by spectral dispersion (SSD) has been proposed to provide the required smoothing.\footnote{J. A. Marozas, J. D. Zuegel, and T. J. B. Collins, Bull. Am. Phys. Soc. \textbf{55}, 294 (2010).} A prototype multi-FM SSD system has been integrated into the NIF-like beamline of the OMEGA EP Laser System. This talk will present recent experimental results to verify smoothing performance by measuring Rayleigh--Taylor growth rates in planar targets of laser-imprinted and pre-imposed surface modulations with and without applying multi-FM SSD. Experimental results will be compared to 2-D \textit{DRACO} simulations using realistic, time-dependent far-field spot-intensity calculations that emulate the effect of SSD. The multi-FM effectiveness in reducing the laser imprint will be inferred and the accuracy of our multi-FM modeling will be assessed. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. [Preview Abstract] |
Friday, November 15, 2013 10:54AM - 11:06AM |
YO4.00008: Hydrodynamic Scaling of the Deceleration-Phase Rayleigh--Taylor Instability A. Bose, R. Nora, K. Woo, R. Betti A 2-D study of the deceleration-phase Rayleigh--Taylor (RT) growth is carried out to assess how the yield-over-clean (YOC) varies in hydro-equivalent implosions. Hydro-equivalent implosions exhibit equal implosion velocity, adiabat, and laser intensity. The YOC indicates the effects of hydrodynamic instabilities on inertial fusion capsule implosions.~While the classical RT instability follows the laws of hydrodynamic similarity (the same growth factor for hydro-equivalent implosions), the effects of ablation and thermal transport in the hot spot cause a deviation from similarity. We present analytic and numerical calculations of the RT growth factors in hydro-equivalent implosions with target sizes varying from typical OMEGA to NIF-scale targets. Theoretical scaling suggests that the deceleration-phase Atwood number and ablation velocity is different for OMEGA and the NIF, yielding growth factors that are dependent on the target size. 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] |
Friday, November 15, 2013 11:06AM - 11:18AM |
YO4.00009: Commissioning a long-duration indirect drive planar platform for highly nonlinear ablative Rayleigh-Taylor experiments on NIF Alexis Casner, V.A. Smalyuk, L. Masse, D. Martinez, S. Liberatore, B. Delorme, J. Kane, L. Jacquet, S. Felker, B. Remington We will present the first results acquired on the National Ignition Facility with a gas-filled room temperature platform driven by 64 beams of the lower half hemisphere. This platform developed under the auspices of the Fundamental Science Program is devoted to the study of the ablative Rayleigh-Taylor Instability (RTI) in transition from weakly nonlinear to highly nonlinear regimes [1]. Simultaneous double axis radiographies (face-on and side-on) are performed on each shot to measure RTI growth and trajectory.. We demonstrate in particular that a 10 ns long radiative temperature plateau at 170 eV has been created which allows to accelerate planar samples over much larger distances and longer time periods than previously achieved. We report on the first face-on measurements for the growth of 2D single-mode modulations and comparison are done with FCI2 postshot simulations. We will discuss the path toward a highly nonlinear bubble merger regime for multimode pattern. \\[4pt] [1] A. Casner et al., Phys. Plasmas 19, 082708 (2012). [Preview Abstract] |
Friday, November 15, 2013 11:18AM - 11:30AM |
YO4.00010: Design of an experiment to measure hydrodynamic instability growth in ICF capsules at the National Ignition Facility Kumar Raman, Vladimir Smalyuk, Daniel Casey, Steven Haan, Bruce Hammel, Omar Hurricane, Hye-Sook Park, J. Luc Peterson, Kyle Peterson, Bruce Remington, Harry Robey A new platform to measure hydrodynamic instability growth on ICF capsules at the National Ignition Facility has been developed and successfully fielded. The concept involves backlit, x-ray imaging of the in--flight growth of a known perturbation machined on an ignition--relevant capsule driven by an ignition--relevant laser pulse. The initial experiments in this platform aimed to measure and compare the growth factor versus mode number dispersion curves of a typical ``low--foot'' drive, resembling what was fielded during the 2011--12 National Ignition Campaign, with a typical ``high--foot'' drive, for which models suggest the RT/RM instability growth is lower. We discuss the design and initial data set of this new platform, and compare with model predictions. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. [Preview Abstract] |
Friday, November 15, 2013 11:30AM - 11:42AM |
YO4.00011: Instability vaccination: A structural design to reduce Rayleigh Taylor instability Amin Esmaeili Instability vaccination can be defined as designing a structure to stimulate the system in order to develop immunity against its instability. In this work we have tried to do this stabilization by a new technique. Previously some suppression of R-M instability was done by insertion of magnetic field, but in this work we have tried to do this suppression by proposing a configuration similar to the shape of instability, we call it instability vaccination. This design will reduce the rotations (mostly rotations of Rayleigh Taylor instability) in the fluids that cause more mixing and instabilities. In this paper, we consider the evolution of the interface between two ideal semi-infinite fluid surfaces, using two-dimensional Riemann solver, to solve the Euler equations. First, we performed evolution of a rectangular disorder between the 2 surfaces using two-dimensional Riemann problem for the equations of Euler. Next, the interface was replaced with a perturbation that was part rectangular and part semi-circular (like a mushroom). The simulation was continued till some time steps using the HLL method. We have seen that the rotations of Rayleigh Taylor (R-T) instability were decreased in the second case. Email: amin@cavelab.cs.tsukuba.ac.jp [Preview Abstract] |
Friday, November 15, 2013 11:42AM - 11:54AM |
YO4.00012: Shockwave-Driven, Supersonic Kelvin-Helmholtz Instability Experiment on OMEGA-EP Wesley Wan, Guy Malamud, Carlos Di Stefano, Carolyn Kuranz, R. Paul Drake Hydrodynamic instabilities are commonly encountered in a variety of high-energy-density systems, including fusion experiments and various astrophysical processes. Shear flow at a fluid interface gives rise to the Kelvin-Helmholtz instability, which then results in mixing between the layers. This talk will cover a recent experiment performed at the OMEGA-EP facility that studied the dampening of the Kelvin-Helmholtz instability as a result of compressibility effects in a high convective Mach number regime. A laser-driven shockwave was used to create shear flow between a low-density foam and high-density plastic. The instability growth was assisted by seeded, single-mode perturbations of varied wavelengths. Our primary diagnostic was x-ray radiography.\\[4pt] This work is funded by the~NNSA-DS and SC-OFES Joint Program in High-Energy-Density Laboratory Plasmas, grant number DE-FG52-09NA29548, and by the National Laser User Facility Program, grant number~DE-NA0000850, with additional support provided under Cooperative Agreement No. DE-FC52-08NA28302 through the Laboratory for Laser Energetics, University of Rochester. [Preview Abstract] |
Friday, November 15, 2013 11:54AM - 12:06PM |
YO4.00013: A Two Dimensional MHD Code Using ALE Method for the Study of Pinch Dynamics Ganghua Wang, Mingxian Kan, Chengwei Sun, Long Xie, Hailong Zhao A two dimensional MHD code MDSC (Magnetically Driven Simulation Code) is developed using ALE method for the study of pinch dynamics. The MHD equations are solved in an operator split fashion or time-splitting technique. The thermal, magnetic diffusions and Lagrangian hydrodynamics are computed with mixed differencing scheme of explicit and implicit. Finite differences are computed with a finite volume technique, and a first-order accurate convection scheme was used. Examples of different seed perturbations showed that the code is successful. [Preview Abstract] |
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