Bulletin of the American Physical Society
58th Annual Meeting of the APS Division of Plasma Physics
Volume 61, Number 18
Monday–Friday, October 31–November 4 2016; San Jose, California
Session JO5: Implosions II |
Hide Abstracts |
Chair: Paul Schmit, Sandia National Laboratories Room: 230 B |
Tuesday, November 1, 2016 2:00PM - 2:12PM |
JO5.00001: Understanding Laser-Imprint Effects on Plastic-Target Implosions on OMEGA with New Physics Models S.X. Hu, D.T. Michel, A.K. Davis, R. Betti, P.B. Radha, E.M. Campbell, D.H. Froula, C. Stoeckl Using the state-of-the-art physics models (nonlocal thermal transport, cross-beam energy transfer, and first-principles equation of state) recently implemented in our two-dimensional hydrocode \textit{DRACO}, we have performed a systematic study of laser-imprint effects on plastic-target implosions on OMEGA by both simulations and experiments. Through varying the laser picket intensity, the imploding shells were set at different adiabats ranging from $\alpha \mbox{\thinspace }=\mbox{\thinspace }2$ to $\alpha \mbox{\thinspace }=\mbox{\thinspace }6.$ As the shell adiabat $\alpha $ decreases, we observed: (1) the measured shell thickness at the hot spot emission becomes larger than the uniform prediction; (2) the hot-spot core emits and neutron burn starts earlier than the corresponding 1-D prediction; and (3) the measured neutron yields are significantly reduced from their 1-D designs. Most of these experimental observations are well reproduced by our \textit{DRACO} simulations with laser imprints. These studies clearly identify that laser imprint is the major cause for target performance degradation of OMEGA implosions of $\alpha \mbox{\thinspace }\le \mbox{\thinspace }3.$ Mitigating laser imprints must be an essential effort to improve low-$\alpha $ target performance in direct-drive inertial confinement fusion ignition attempts. 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 1, 2016 2:12PM - 2:24PM |
JO5.00002: High-Z Coating Experiments on Omega EP Max Karasik, J. Oh, C. Stoeckl, A. J. Schmitt, Y. Aglitskiy, S. P. Obenschain Previous experiments on Nike KrF laser ($\lambda$=248nm) at NRL found that a thin ($400–-800\AA$) high-Z (Au or Pd) overcoat on the target is effective in suppressing broadband imprint[Obenschain, et al, PoP 2002, Karasik, et al, PRL 2015]. Implementation of this technique on the tripled Nd:glass (351nm) NIF would enable higher uniformity direct-drive experiments there. To this end, we are carrying out experiments using the NIF-like beams of Omega EP. On Nike, a low-intensity, highly smooth prepulse heats and pre-expands the low thermal mass metallic coating to $\sim100$um scale length. This likely improves imprint reduction for longer spatial scales because of increased distance between laser absorption and the ablation surface. The $3\omega$ beams of Omega EP do not have this feature due to nonlinear harmonic conversion. We introduced a means of pre-expanding the high-Z coating to similar length scale on Omega EP using a soft x-ray prepulse, generated by irradiating an auxiliary Au foil 1cm in front of the main target tens of ns prior to the main target drive. Coating dynamics are measured using side-on radiography. The effectiveness of pre-expansion on imprint reduction will be assessed by measurements of the RT-amplified imprint using monochromatic curved crystal radiography. [Preview Abstract] |
Tuesday, November 1, 2016 2:24PM - 2:36PM |
JO5.00003: Three-Dimensional Evaluation of Laser Imprint in National Ignition Facility Multi-FM Smoothing by Spectral Dispersion Experiments A. Shvydky, M. Hohenberger, P.B. Radha, M.J. Rosenberg, K.S. Anderson, V.N. Goncharov, J.A. Marozas, F.J. Marshall, P.W. McKenty, S.P. Regan, T.C. Sangster, J.M. Koning, M.M. Marinak, L. Masse Control of shell nonuniformities imprinted by a laser and amplified by hydrodynamic instabilities in an imploding target is critical for the success of direct-drive ignition at the National Ignition Facility (NIF). One-dimensional, multi-FM smoothing by spectral dispersion (SSD), proposed to provide the required level of smoothing of the laser imprint, has been integrated into one quad of the NIF Laser System and used in recent experiments. The experiments employed flat CH foils driven with a single NIF quad with either the multi-FM or stimulated Brillouin scattering suppression SSD. Face-on x-ray radiography was used to measure optical-depth variations, from which the amplitudes of the foil areal-density modulations were obtained. Results of 3-D, radiation--hydrodynamics code \textit{HYDRA}\footnote{M. M. Marinak \textit{et al}., Phys. Plasmas \textbf{8}, 2275 (2001).\par } simulations of the growth of the imprint seeded perturbations are presented and compared with the experimental data. The effectiveness of the multi-FM SSD in reducing the imprint is evaluated. 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 1, 2016 2:36PM - 2:48PM |
JO5.00004: Ultra-high mode mix in low-adiabat National Ignition Facility National Ignition Campaign implosions Robert Scott This work re-examines a sub-set of the `slow-rise', low adiabat implosions from the National Ignition Campaign using the Hyades radiation-hydrodynamics code in an effort to better understand potential phenomenological sources of `excess' mix observed experimentally. An extensive effort has been made to match both shock-timing and backlit radiography (Con-A) implosion data in an effort to reproduce the experimental conditions as accurately as possible. A \textasciitilde 30{\%} reduction in ablation pressure at peak drive is required to match the experimental data. This reduced ablation pressure allows the ablator to decompress, in turn causing the DT ice-ablator interface to go Rayleigh-Taylor unstable early in the implosion acceleration phase. Post-processing the runs with various mix models indicates high-mode mix from the DT ice-ablator interface may penetrate deep into the hotspot. This work offers a potential explanation of why these low adiabat implosions exhibited significantly higher levels of mix than expected from high-fidelity multi-dimensional simulations. Through this new understanding a possible route forward for low-adiabat implosions on NIF is suggested. [Preview Abstract] |
Tuesday, November 1, 2016 2:48PM - 3:00PM |
JO5.00005: Hydrodynamic response from oxygen non-uniformities in glow-discharge polymer (GDP) plastic in OMEGA OHRV experiments Suzanne Ali, Peter Celliers, Steve Haan, Salman Baxamusa, Michael Johnson, Jim Hughes, Hannah Reynolds, Brian Watson Simulations and target characterization indicated that inhomogeneity in oxygen content could be a significant seed for Rayleigh-Taylor growth in GDP-ablator NIF implosions. This has been indirectly supported by observation of larger than expected in-flight modulations during NIF GDP capsule implosions, and the realization that such inhomogeneities can result from photo-induced oxygen uptake. In order to investigate the magnitude of the effect of these oxygen heterogeneities on the hydrodynamic response of GDP ablators, oxygen modulations were photo-induced in GDP foils by illuminating the foils with blue light through a periodic mask pattern. The foils were then used as ablators driven on OMEGA by a halfraum to replicate foot conditions on NIF. The resulting optically reflective shock wave was observed using the OMEGA High Resolution Velocimeter (OHRV). Two-dimensional velocity maps were obtained for both oxygen-modulated and unmodulated samples, with the modulated samples showing clear evidence of the propagation of a rippled shock wave as a result of the photo-induced oxygen heterogeneity. [Preview Abstract] |
Tuesday, November 1, 2016 3:00PM - 3:12PM |
JO5.00006: A connection between mix and adiabat in ICF capsules Baolian Cheng, Thomas Kwan, Yi-Ming Wang, Sunghuan (Austin) Yi, Steven Batha We study the relationship between instability induced mix, preheat and the adiabat of the deuterium-tritium (DT) fuel in fusion capsule experiments. Our studies show that hydrodynamic instability not only directly affects the implosion, hot spot shape and mix, but also affects the thermodynamics of the capsule, such as, the adiabat of the DT fuel, and, in turn, affects the energy partition between the pusher shell (cold DT) and the hot spot. It was found that the adiabat of the DT fuel is sensitive to the amount of mix caused by Richtmyer-Meshkov (RM) and Rayleigh-Taylor (RT) instabilities at the material interfaces due to its exponential dependence on the fuel entropy. An upper limit of mix allowed maintaining a low adiabat of DT fuel is derived. Additionally we demonstrated that the use of a high adiabat for the DT fuel in theoretical analysis and with the aid of 1D code simulations could explain some aspects of the 3D effects and mix in the capsule experiments. Furthermore, from the observed neutron images and our physics model, we could infer the adiabat of the DT fuel in the capsule and determine the possible amount of mix in the hot spot (LA-UR-16-24880). [Preview Abstract] |
Tuesday, November 1, 2016 3:12PM - 3:24PM |
JO5.00007: ABSTRACT WITHDRAWN |
Tuesday, November 1, 2016 3:24PM - 3:36PM |
JO5.00008: ABSTRACT WITHDRAWN |
Tuesday, November 1, 2016 3:36PM - 3:48PM |
JO5.00009: Rayleigh-Taylor mixing with time-dependent acceleration Snezhana Abarzhi We extend the momentum model to describe Rayleigh-Taylor (RT) mixing driven by a time-dependent acceleration. The acceleration is a power-law function of time, similarly to astrophysical and plasma fusion applications. In RT flow the dynamics of a fluid parcel is driven by a balance per unit mass of the rates of momentum gain and loss. We find analytical solutions in the cases of balanced and imbalanced gains and losses, and identify their dependence on the acceleration exponent. The existence is shown of two typical regimes of self-similar RT mixing –acceleration-driven Rayleigh-Taylor-type and dissipation-driven Richtymer-Meshkov-type with the latter being in general non-universal. Possible scenarios are proposed for transitions from the balanced dynamics to the imbalanced self-similar dynamics. Scaling and correlations properties of RT mixing are studied on the basis of dimensional analysis. Departures are outlined of RT dynamics with time-dependent acceleration from canonical cases of homogeneous turbulence as well as blast waves with first and second kind self-similarity. [Preview Abstract] |
Tuesday, November 1, 2016 3:48PM - 4:00PM |
JO5.00010: Highly symmetric interfacial structures in Rayleigh Taylor instability with time-dependent acceleration Aklant K. Bhowmick, Snezhana Abarzhi Rayleigh Taylor instability in a power-law time dependent acceleration field is investigated for a flow with the symmetry group p6mm (hexagonal) in the plane normal to acceleration. The Regular asymptotic solutions form a one-parameter family and the physically significant solution is identified with the one having the fastest growth and being stable (bubble tip velocity). Two distinct regimes are identified dependent on the acceleration exponent, the RM-type regime, where the dynamics is identical to conventional RM instability and is dominated by initial conditions, and the RT-type regime where the dynamics is dominated by the acceleration term. For the latter, the time dependence has profound effects on the dynamics. In the RT non-linear regime, the time dependence has no consequence on the morphology of the bubbles but the growth rate (bubble tip velocity) evolves as power law with the exponent set by the acceleration. The solutions for a one-parameter family, and are convergent with exponential decay of Fourier amplitudes close to the physical solution. The solutions are stable at maximum tip velocity and flat bubbles are unstable, and the growth/decay of perturbations is no longer purely exponential and depends on the acceleration exponent. [Preview Abstract] |
Tuesday, November 1, 2016 4:00PM - 4:12PM |
JO5.00011: Molecular Dynamics Investigations of the Ablator/Fuel Interface during Early Stages of Inertial Confinement Fusion Liam Stanton, James Glosli, Michael Murillo At the National Ignition Facility, high-powered laser beams are used to compress a small target to generate fusion reactions. A critical issue in achieving this is the understanding of mix at the ablator/fuel interface. Mixing occurs at various length scales, ranging from atomic inter-species diffusion to hydrodynamic instabilities. Because the interface is preheated by energy from the incoming shock, it is important to understand the dynamics before the shock arrives. The interface is in the warm dense matter phase with a deuterium/tritium fuel mixture on one side and a plastic mixture on the other. We would like to understand various aspects of the evolution, including the state of the interface when the main shock arrives, the role of electric field generation at the interface, and the character and time scales for diffusion. We present a multiscale approach to model these processes, which combines molecular dynamics to simulate the ionic degrees of freedom with orbital-free density functional theory to calculate the electronic structure. Simulation results are presented and connections to hydrodynamic models are discussed. [Preview Abstract] |
Tuesday, November 1, 2016 4:12PM - 4:24PM |
JO5.00012: A 2D and 3D Code Comparison of Turbulent Mixing in Spherical Implosions Markus Flaig, Ben Thornber, Brian Grieves, David Youngs, Robin Williams, Dan Clark, Chris Weber Turbulent mixing due to Richtmyer-Meshkov and Rayleigh-Taylor instabilities has proven to be a major obstacle on the way to achieving ignition in inertial confinement fusion (ICF) implosions. Numerical simulations are an important tool for understanding the mixing process, however, the results of such simulations depend on the choice of grid geometry and the numerical scheme used. In order to clarify this issue, we compare the simulation codes FLASH, TURMOIL, HYDRA, MIRANDA and FLAMENCO for the problem of the growth of single- and multi-mode perturbations on the inner interface of a dense imploding shell. We consider two setups: A single-shock setup with a convergence ratio of $\sim$4, as well as a higher convergence multi-shock setup that mimics a typical NIF mixcap experiment. We employ both singlemode and ICF-like broadband perturbations. We find good agreement between all codes concerning the evolution of the mix layer width, however, the are differences in the small scale mixing. We also develop a Bell-Plesset model that is able to predict the mix layer width and find excellent agreement with the simulation results. [Preview Abstract] |
Tuesday, November 1, 2016 4:24PM - 4:36PM |
JO5.00013: Interfacial mixing in high energy density matter with a new kinetic model Jeffrey Haack, Cory Hauck, Michael Murillo We apply a new conservative multi-species multi-temperature BGK model to study interface mixing in a dense plasma with ICF applications. This model conserves mass, momentum, and kinetic energy and allows for a more clear connection to the underlying cross sections and inter-species collision rates. In particular, this example exhibits hydrogen jetting into the fusion fuel. We compare with molecular dynamics results. [Preview Abstract] |
Tuesday, November 1, 2016 4:36PM - 4:48PM |
JO5.00014: Modeling laser produced plasmas with smoothed particle hydrodynamics for next generation advanced light sources Robert Holladay, Alec Griffith, Michael S. Murillo A computational model has been developed to study the evolution of a plasma generated by next-generation advanced light sources such as SLAC's LCLS and LANL's proposed MaRIE. Smoothed Particle Hydrodynamics (SPH) is used to model the plasma evolution because of the ease with which it handles the open boundary conditions and large deformations associated with these experiments. Our work extends the basic SPH method by utilizing a two-fluid model of an electron-ion plasma that also incorporates time dependent ionization and recombination by allowing the SPH fluid particles to have an evolving mass based on the mean ionization state of the plasma. Additionally, inter-species heating, thermal conduction, and electric fields are also accounted for. The effects of various initial conditions and model parameters will be presented, with the goal of using this framework to develop a model that can be used in the design and interpretation of future experiments. [Preview Abstract] |
Tuesday, November 1, 2016 4:48PM - 5:00PM |
JO5.00015: Dimensional crossover in Richtmyer-Meshkov flows Katsunobu Nishihara, Aklant Bhowmick, Snezhana Abarzhi We analyze nonlinear dynamics of large scale coherent structures in Richtmyer-Meshkov flows. Group theoretic analysis is applied with a detailed consideration of p2mm (3D rectangular), p4mm (3D square) and pm1 (2D). Symmetry dictates that asymptotic solutions form a 2 parameter family for rectangular flows and a 1 parameter family for 3D square and 2D flows. For 3D square and 2D symmetry, asymptotic solutions are obtained for the 1st and 2nd order of approximation and the fastest growth rate occurs at zero bubble curvatures. Fourier amplitudes exponentially decay with increase in order showing that solutions are convergent. Both 2D and 3D square solutions are stable with respect to symmetry conserving perturbations. Isotropic 3D square solutions are universally stable, while 2D solutions are unstable to anisotropic perturbations. Furthermore, the 3D and 2D solutions cannot be continuously transformed from one form to another and the dimensional crossover is discontinuous. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700