Bulletin of the American Physical Society
59th Annual Meeting of the APS Division of Plasma Physics
Volume 62, Number 12
Monday–Friday, October 23–27, 2017; Milwaukee, Wisconsin
Session YO7: Hydrodynamic Instability II/Compression and Burn III |
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Chair: Channing Huntington, Lawrence Livermore National Laboratory Room: 203AB |
Friday, October 27, 2017 9:30AM - 9:42AM |
YO7.00001: A Model for the Growth of Localized Shell Features in Inertial Confinement Fusion Implosions V.N. Goncharov Engineering features and target debris on inertial confinement fusion capsules play detrimental role in target performance. The contact points of such features with target surface as well as shadowing effects\footnote{ A. G. MacPhee \textit{et al}., Phys. Rev. E \textbf{95}, 031204(R) (2017).}$^{\mathrm{\thinspace }}$produce localized shell nonuniformities that grow in time because of the Rayleigh--Taylor instability developed during shell acceleration. Such growth leads to significant mass modulation in the shell and injection of ablator and cold fuel material into the target vapor region. These effects are commonly modeled using 2-D and 3-D hydrodynamic codes that take into account multiple physics effects. Such simulations, however, are very challenging since in many cases they are inherently three dimensional (as in the case of fill tube or stalk shadowing) and require very high grid resolution to accurately model short-scale features. To gain physics insight, an analytic model describing the growth of these features has been developed. The model is based on the Layzer-type approach.\footnote{ V. N. Goncharov and D. Li, Phys. Rev. E \textbf{71}, 046306 (2005).} The talk will discuss the results of the model used to study perturbation growth seeded by localized target debris, glue spots, fill tubes, and stalks. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. [Preview Abstract] |
Friday, October 27, 2017 9:42AM - 9:54AM |
YO7.00002: Fill Tube Dynamics in Inertial Confinement Fusion Implosions with High Density Carbon Ablators Kevin Baker, Cliff Thomas, Tom Dittrich, Chris Weber, Tod Woods, Chris Mauche, Dan Casey, Shahab Khan, Matthias Hohenberger, Brian Spears, Charles Yeamans, John Moody, Alastair Moore, Nathan Meezan, Benjamin Bachmann, Robin Benedetti, Niko Izumo, Tammy Ma, Sabrina Nagel, Art Pak High density carbon, HDC, ablator experiments performed on the National Ignition Facility typically have a feature seen in the hotspot x-ray self-emission which correlates with the position of the capsule's fill tube. This presentation focuses on one such shot which used an undoped HDC ablator with a 50/50 deuterium/tritium fill. This combination produced experimental hotspot images in which the limb brightening of the hotspot images could be seen in conjunction with the fill tube feature penetrating to the center of the hotspot and the indentation in the capsule about the fill tube. These experimental images will be presented along with analysis of the motion of the fill tube feature relative to the time-dependent hotspot diameter. Comparison to computer simulations and in particular what these simulations imply with regard to the level of m-band required in the codes to more accurately reproduce the time-dependent experimental images will also be presented. 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] |
Friday, October 27, 2017 9:54AM - 10:06AM |
YO7.00003: Design options for reducing the impact of the fill-tube in ICF implosion experiments on the NIF Christopher R. Weber, L.F. Berzak Hopkins, D.T. Casey, D.S. Clark, B.A. Hammel, S. Le Pape, A. MacPhee, J. Milovich, L.A. Pickworth, H.F. Robey, V.A. Smalyuk, M. Stadermann, S.J. Felker, A. Nikroo, C.A. Thomas, J. Crippen, N. Rice Inertial Confinement Fusion (ICF) capsules on the National Ignition Facility (NIF) are filled with thermonuclear fuel through a fill-tube. When the capsule implodes, perturbations caused by the fill-tube allow ablator material to mix into the hot spot and reduce fusion performance. This talk will explore several design options that attempt to reduce this damaging effect. Reducing the diameter of the fill-tube and its entrance hole is the obvious course and has been tested in experiments. Simulations also show sensitivity to the amount of glue holding the fill-tube to the capsule and suggest that careful control of this feature can limit the amount of injected mass. Finally, an off-axis fill-tube reduces the initial squirt of material into the fuel and may be a way of further optimizing this engineering feature. [Preview Abstract] |
Friday, October 27, 2017 10:06AM - 10:18AM |
YO7.00004: Mitigate the tent-induced perturbation in ignition capsules by supersonic radiation propagation Zhensheng Dai, Jianfa Gu, Wudi Zheng In the inertial confinement fusion (ICF) scheme, to trap the alpha particle products of the D-T reaction, the capsules needs to be imploded and compressed with high symmetry In the laser indirect drive scheme, the capsules are held at the center of high-Z hohlraums by thin membranes (tents). However, the tents are recognized as one of the most important contributors to hot spot asymmetries, areal density perturbations and reduced performance. To improve the capsule implosion performance, various alternatives such as the micro-scale rods, a larger fill-tube and a low-density foam layer around the capsule have been presented. Our simulations show that the radiation propagates supersonically in the low-density foam layer and starts to ablate the capsule before the perturbations induced by the tents reach the ablating fronts. The tent induced perturbations are remarkably weakened when they are propagating in the blow-off plasma. [Preview Abstract] |
Friday, October 27, 2017 10:18AM - 10:30AM |
YO7.00005: A comparison of hydro-instabilities in CH, HDC, and beryllium ablators on NIF V. A. Smalyuk, H. F. Robey, S. Ali, L. F. Berzak Hopkins, D. T. Casey, P. M. Celliers, D. S. Clark, S. J. Felker, J. E. Field, S. W. Haan, B. A. Hammel, W. W. Hsing, J. J. Kroll, O. L. Landen, S. LePape, A. G. MacPhee, D. Martinez, J. Milovich, A. Nikroo, L. Pickworth, M. Stadermann, C. R. Weber, J. Kline, E. Loomis, A. Yi A comparison of the hydrodynamic growth in plastic, high-density carbon, and beryllium ablators will be presented in indirect-drive implosions on National Ignition Facility. This comparison is based on experimentally measured instabilities in all phases of implosions for the three ablators. The 2-D and 3-D perturbations were measured at the ablation-surface with the Hydrodynamic Growth Radiography platform. In the deceleration phase of implosions, innovative self-emission and ``self-backlight'' techniques were used. Results of the 3-D perturbation growth including engineering features will also be presented for convergence up to 20 and compared for the three ablators. [Preview Abstract] |
Friday, October 27, 2017 10:30AM - 10:42AM |
YO7.00006: High-resolution Imaging of Deuterium-Tritium Capsule Implosions on the National Ignition Facility Benjamin Bachmann, Ryan Rygg, Gilbert Collins, Pravesh Patel Highly-resolved 3-D simulations of inertial confinement fusion (ICF) implosions predict a hot spot plasma that exhibits complex micron-scale structure originating from a variety of 3-D perturbations [1]. Experimental diagnosis of these conditions requires high spatial resolution imaging techniques. X-ray penumbral imaging can improve the spatial resolution over pinhole imaging while simultaneously increasing the detected photon yield at x-ray energies where the ablator opacity becomes negligible [2]. Here we report on the first time-integrated x-ray penumbral imaging experiments of ICF capsule implosions at the National Ignition Facility that achieved spatial resolution as high as 4 micrometer. 6 to 30 keV hot spot images from layered DT implosions will be presented from a variety of experimental ICF campaigns, revealing previously unseen detail. It will be discussed how these and future results can be used to improve our physics understanding of inertially confined fusion plasmas by enabling spatially resolved measurements of hot spot properties, such as radiation energy, temperature or derived quantities. [1] D. S. Clark \textit{etal.}, Phys. Plasmas 22, 022703 (2015) [2] B. Bachmann \textit{etal.}, RSI. 87, 11E201 (2016) [Preview Abstract] |
Friday, October 27, 2017 10:42AM - 10:54AM |
YO7.00007: Direct-Drive DT Cryogenic Implosion Performance with a Fill Tube S.P. Regan, D. Cao, V.N. Goncharov, K.S. Anderson, R. Betti, M.J. Bonino, E.M. Campbell, T.J.B. Collins, R. Epstein, C.J. Forrest, V.Yu. Glebov, D. Harding, S.X. Hu, I.V. Igumenshchev, J.A. Marozas, F.J. Marshall, P.W. McKenty, P.B. Radha, T.C. Sangster, C. Stoeckl, R.W. Luo, A. Tambazidis, M.E. Schoff, M. Farrell The effects of a fill tube on the performance of direct-drive DT cryogenic implosions on the 60-beam, 30-kJ, 351-nm OMEGA laser are presented. The calculated adiabat, convergence ratio, and in-flight-aspect ratio quantities were $\sim $4, $\sim $17, and $\sim $23, respectively. Changes to the measured neutron yield, areal density, and ion temperature caused by the fill tube were found to be within experimental uncertainties. Gated x-ray images recorded during the acceleration phase at photon energies down to $\sim $1 keV show evidence of the fill tube perturbing the imploding shell and causing a region of enhanced emission from the hot spot, while gated x-ray images of the hot spot in the 4- to 8-keV photon energy range show no effect from the fill tube. This material is based upon work supported by the Department Of Energy National Nuclear Security Administration under Award Number DE{\-}NA0001944. [Preview Abstract] |
(Author Not Attending)
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YO7.00008: Diffusive tunneling for alleviating Knudsen-layer reactivity reduction under hydrodynamic mix Xianzhu Tang, Chris McDevitt, Zehua Guo Hydrodynamic mix will produce small features for intermixed deuterium-tritium fuel and inert pusher materials. The geometrical characteristics of the mix feature have a large impact on Knudsen layer yield reduction. We considered two features. One is planar structure, and the other is fuel cells segmented by inert pusher material which can be represented by a spherical DT bubble enclosed by a pusher shell. The truly 3D fuel feature, the spherical bubble, has the largest degree of yield reduction, due to fast ions being lost in all directions. The planar fuel structure, which can be regarded as 1D features, has modest amount of potential for yield degradation. While the increasing yield reduction with increasing Knudsen number of the fuel region is straightforwardly anticipated, we also show, by a combination of direct simulation and simple model, that once the pusher materials is stretched sufficiently thin by hydrodynamic mix, the fast fuel ions diffusively tunnel through them with minimal energy loss, so the Knudsen layer yield reduction becomes alleviated. This yield recovery can occur in a chunk-mixed plasma, way before the far more stringent, asymptotic limit of an atomically homogenized fuel and pusher assembly. [Preview Abstract] |
Friday, October 27, 2017 11:06AM - 11:18AM |
YO7.00009: Sensitivity of Gas-Ablator Mix to Shock Merger Depth in 2-Shock Symcaps at the National Ignition Facility T. Ma, S. A. MacLaren, J. D. Salmonson, D. Ho, S. F. Khan, L. Masse, J. E. Pino, J. E. Ralph, C. Czajka, R. E. Tipton, G. A. Kyrala The HED 2-Shock implosion campaign was developed on the National Ignition Facility as a relatively robust and well-behaved nearly one-dimensional, low convergence, symmetric platform by employing a two-shock pulseshape in a low gas-fill hohlraum and a large case-to-capsule (hohlraum-to-capsule size) ratio. Additionally, the relatively thick capsule shell (low aspect ratio of 3.9) combined with the temperature of the foot of the laser pulse (\textasciitilde 120 eV) essentially eliminates ablation front instability growth. The result is a platform that is well suited to the study of mixing at the gas-ablator interface without the complications of low mode asymmetries or mix feedthrough. A layer of CD plastic on the inner surface of the CH shell filled with a mixture of H and T allows for the inference of gas-ablator mix via the measurement of DD and DT neutron yields. By advancing or retracting the time of launch of the second shock, the depth into the capsule at which the two shocks merge can be systematically varied from the shell to the gas. The effect of this, and possible rebound shocks, on inducing mix at the gas-ablator interface is studied. Details and results of these experiments will be described. [Preview Abstract] |
Friday, October 27, 2017 11:18AM - 11:30AM |
YO7.00010: Update on 2-D OMEGA Capsule Implosions Paul Bradley We have an upgraded laser energy deposition package in our AMR-Eulerian radiation-hydrodynamic code called RAGE. As part of our validation effort, we ran 2-D simulations for a series of OMEGA direct drive implosion capsules that have shell thickness ranging from 7.2 to 29.3 $\mu$m and different gas fills. These simulations include the effect of surface roughness, laser spot non-uniformity, the mounting stalk, and the glue spot. We examined the sensitivity of our simulated results to mesh resolution and mix model. Our simulated results compare well to the experimental yield, ion temperature, burn width, and x-ray size data. [Preview Abstract] |
Friday, October 27, 2017 11:30AM - 11:42AM |
YO7.00011: Effect of Symmetry on Performance of Imploding Capsules using the Big Foot Design Shahab Khan, Daniel Casey, Kevin Baker, Cliff Thomas, Ryan Nora, Brian Spears, Laura Benedetti, Nobuhiko Izumi, Tammy Ma, Sabrina Nagel, Arthur Pak At the National Ignition Facility, several simultaneous designs are investigated for optimizing Inertial Confinement Fusion (ICF) energy gain of indirectly driven imploding fuel capsules. Relatively high neutron yield has been achieved while exhibiting a non-symmetric central core and/or shell. While developing the ``Big Foot'' design, several tuning steps were undertaken to minimize the asymmetry of both the central hot core as well as the shell. Surrogate capsules (symcaps) were utilized in the 2-D Radiography platform to assess both the shell and central core symmetry. The results of the tuning experiments are presented. In addition, a comparison of performance and shape metrics demonstrates that improving symmetry of the implosion can yield better performance. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. LLNL-ABS-683471 [Preview Abstract] |
Friday, October 27, 2017 11:42AM - 11:54AM |
YO7.00012: Initial Findings on Hydrodynamic Scaling Extrapolations of National Ignition Facility BigFoot Implosions R. Nora, J. E. Field, J. Luc Peterson, B. Spears, M. Kruse, K. Humbird, J. Gaffney, P. T. Springer, S. Brandon, S. Langer We present an experimentally corroborated hydrodynamic extrapolation of several recent BigFoot implosions on the National Ignition Facility. An estimate on the value and error of the hydrodynamic scale necessary for ignition (for each individual BigFoot implosion) is found by hydrodynamically scaling a distribution of multi-dimensional HYDRA simulations whose outputs correspond to their experimental observables. The 11-parameter database of simulations, which include arbitrary drive asymmetries, dopant fractions, hydrodynamic scaling parameters, and surface perturbations due to surrogate tent and fill-tube engineering features, was computed on the TRINITY supercomputer at Los Alamos National Laboratory. This simple extrapolation is the first step in providing a rigorous calibration of our workflow to provide an accurate estimate of the efficacy of achieving ignition on the National Ignition Facility. [Preview Abstract] |
Friday, October 27, 2017 11:54AM - 12:06PM |
YO7.00013: Using deep neural networks to augment NIF post-shot analysis Kelli Humbird, Luc Peterson, Ryan McClarren, John Field, Jim Gaffney, Michael Kruse, Ryan Nora, Brian Spears Post-shot analysis of National Ignition Facility (NIF) experiments is the process of determining which simulation inputs yield results consistent with experimental observations. This analysis is typically accomplished by running suites of manually adjusted simulations, or Monte Carlo sampling surrogate models that approximate the response surfaces of the physics code. These approaches are expensive and often find simulations that match only a small subset of observables simultaneously. We demonstrate an alternative method for performing post-shot analysis using inverse models, which map directly from experimental observables to simulation inputs with quantified uncertainties. The models are created using a novel machine learning algorithm which automates the construction and initialization of deep neural networks to optimize predictive accuracy. We show how these neural networks, trained on large databases of post-shot simulations, can rigorously quantify the agreement between simulation and experiment. 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, October 27, 2017 12:06PM - 12:18PM |
YO7.00014: Statistical Relations for Yield Degradation in Inertial Confinement Fusion K.M. Woo, R. Betti, D. Patel, V. Gopalaswamy In inertial confinement fusion (ICF), the yield-over-clean (YOC) is a quantity commonly used to assess the performance of an implosion with respect to the degradation caused by asymmetries. The YOC also determines the Lawson parameter\footnote{ P. Y. Chang \textit{et al.}, Phys. Rev. Lett. \textbf{104}, 135002 (2010).} used to identify the onset of ignition and the level of alpha heating in ICF implosions. In this work, we show that the YOC is a unique function of the residual kinetic energy in the compressed shell (with respect to the 1-D case) regardless of the asymmetry spectrum. This result is derived using a simple model of the deceleration phase as well as through an extensive set of 3-D radiation--hydrodynamics simulations using the code \textit{DEC3D}. The latter has been recently upgraded to include a 3-D spherical moving mesh, the \textit{HYPRE} solver for 3-D radiation transport and piecewise-parabolic method for robust shock-capturing hydrodynamic simulations. \textit{DEC3D} is used to build a synthetic single-mode database to study the behavior of yield degradation caused by Rayleigh--Taylor instabilities in the deceleration phase. The relation between YOC and residual kinetic energy is compared with the result in an adiabatic implosion model. The statistical expression of YOC is also applied to the ignition criterion in the presence of multidimensional nonuniformities. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. [Preview Abstract] |
Friday, October 27, 2017 12:18PM - 12:30PM |
YO7.00015: Definition of Ignition in Inertial Confinement Fusion A.R. Christopherson, R. Betti Defining ignition in inertial confinement fusion (ICF) is an unresolved problem. In ICF, a distinction must be made between the ignition of the hot spot and the propagation of the burn wave in the surrounding dense fuel. Burn propagation requires that the hot spot is robustly ignited and the dense shell exhibits enough areal density. Since most of the energy gain comes from burning the dense shell, in a scale of increasing yields, hot-spot ignition comes before high gains. Identifying this transition from hot-spot ignition to burn-wave propagation is key to defining ignition in general terms applicable to all fusion approaches that use solid DT fuel. \textit{Ad hoc} definitions such as gain $=$ 1 or doubling the temperature are not generally valid. In this work, we show that it is possible to identify the onset of ignition through a unique value of the yield amplification defined as the ratio of the fusion yield including alpha-particle deposition to the fusion yield without alphas. Since the yield amplification is a function of the fractional alpha energy $f_{\alpha } ={E_{\alpha } } \mathord{\left/ {\vphantom {{E_{\alpha } } {2E_{\mbox{hs}} }}} \right. \kern-\nulldelimiterspace} {2E_{\mbox{hs}} }$ (a measurable quantity), it appears possible not only to define ignition but also to measure the onset of ignition by the experimental inference of the ~fractional alpha energy and yield amplification. This material is based upon work supported by the Department of Energy Office of Fusion Energy Services under Award Number DE-FC02-04ER54789 and National Nuclear Security Administration under Award Number DE-NA0001944. [Preview Abstract] |
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