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 GO5: Implosions I |
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Chair: Tammy Ma, Lawrence Livermore National Laboratory Room: 230 B |
Tuesday, November 1, 2016 9:30AM - 9:42AM |
GO5.00001: Systematic Fuel Cavity Asymmetries in Directly Driven ICF Implosions Rahul Shah, F. J. Wysocki, B. M. Haines, J. F. Benage, J. Fooks, V. Glebov, P. Hakel, M. Hoppe, I. V. Igumenshchev, G. Kagan, R. C. Mancini, F. J. Marshall, D. T. Michel, T. J. Murphy, M. E. Schoff, C. Stoeckl, B. Yaakobi Direct-drive ICF could provide the additional energy needed for ignition. However, sub-scale experiments have reached only half the expected pressure. Simulations suggest asymmetry as the culprit [1]. Herein we assess symmetry by use of a novel imaging technique enabling diagnosis of the fuel-cavity shape as defined at the fuel-shell interface. In this approach, targets are slightly modified such that a Ti tracer layer is selectively placed only at the innermost surface of the ablator. The specificity of the emission to the fuel-shell interface, coupled with spectrally selective imaging, leads us to profoundly new imaging evidence asymmetries. Identifications are made with anticipated systematic asymmetries of shape during deceleration at convergence $\sim$15. An $\ell\sim1$ systematic asymmetry is revealed suggesting evidence of a blow-out which quashes pressure. [1] I. V. Igumenshchev \textit{et. al.} Phys. Plasmas \textbf{23}, 052702 (2016). [Preview Abstract] |
Tuesday, November 1, 2016 9:42AM - 9:54AM |
GO5.00002: Visualizing density perturbations in the capsule shell in NIF implosions near peak velocity L.A. Pickworth, B.A. Hammel, V.A. Smalyuk, A. MacPhee, H.A. Scott, H.F. Robey, J. Field, M. Barrios, S.P. Regan Engineering features on the capsule (surface roughness, support structures, etc.) can introduce outer surface perturbations that are ultimately detrimental to the performance of the capsule. Recent experiments have assessed minimal support structures and alternate pulse shapes using a re-entrant cone and back lighter that is perturbing to the implosion below radii of $\sim 500$ $\mu$ m. Emission from the hot core, after shock-stagnation and prior to peak velocity (PV), has been used as a self-backlighter, providing a means to sample one side of the capsule at smaller radii. Adding high-Z gas ($\sim 1\%$ Ar) to the capsule fill in Symcaps (4He), has produced a continuum backlighter with significant increase in emission at $hv$$\sim 8$ keV over nominal fills. High-resolution imaging diagnostics with photon energy selectivity form 2D images of the transmitted self-emission, above and below the K-edge of an internally doped Cu layer. We can infer from these images the growth at PV of outer surface perturbations. [Preview Abstract] |
Tuesday, November 1, 2016 9:54AM - 10:06AM |
GO5.00003: Pushered single shell capsule design for the study of high Z mix on the National Ignition Facility Ryan Sacks, Kevin Baker, Daniel Casey, Edward Dewald, Frank Graziani, Stephan MacLaren, Abass Nikroo, Jesse Pino, Joseph Ralph, Bruce Remington, Jay Salmonson, Vladimir Smalyuk, Robert Tipton Alternative ignition scenarios on the NIF such as double shells [1,2] require an understanding of the mix between high-Z capsule shell and DT gas. By utilizing the two-shock platform, which has been shown to be a robust, symmetric, and near 1-D implosion [3], a new design is developed to explore high Z mix. Through the addition of a Ge doped pusher layer on the inner surface of the capsule, mixing of non-fully ionized material can be measured using x-ray emission, nuclear yield diagnostics developed during the CD mix experiments [4], and characterization of the central core. Using the two-shock design allows for the results to be separated from possible implosion asymmetries, allowing differences in performance between capsules with and without Ge to be attributed to high Z material mixing. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344, Lawrence Livermore National Security, LLC. IM number LLNL-ABS-697758. [1] P.A. Amendt, J.D. Colvin \textit{et al.,} Phys. Plasmas \textbf{9}, 2221 (2002) [2] H.F. Robey, P.A. Amendt \textit{et al.,} Phys. Rev. Lett. \textbf{103}, 145003 (2009) [3] S.F. Khan, S.A. MacLaren \textit{et al.}, Phys. Plasmas \textbf{23}, 042708 (2016) [4] D.T. Casey, V.A. Smalyuk \textit{et al}., Phys. Plasmas \textbf{21}, 092705 (2014) [Preview Abstract] |
Tuesday, November 1, 2016 10:06AM - 10:18AM |
GO5.00004: The Measurable Effects of Germanium Loaded into the Pusher of a Pushered Single Shell Capsule Designed for the National Ignition Facility Robert Tipton, Kevin Baker, Daniel Casey, Eduard Dewald, Frank Graziani, Steve MacLaren, Abass Nikroo, Jesse Pino, Joe Ralph, Bruce Remington, Ryan Sacks, Jay Salmonson, Vladimir Smalyuk Germanium loaded pushered single shells (PSS) have been designed as a vehicle to study the effects of turbulent mixing between the DT fuel and a pusher which is not fully ionized. This is intended as a surrogate for the high-Z mixing expected in future double-shell ignition capsules [1]. These PSS experiments will be diagnosed by loading deuterium along with the germanium into the GDP pusher and filling the capsule with a mixture of tritium and hydrogen. In such CD mix experiments, the measured number of DT neutrons along with the inferred ion temperature from the time-of-flight thermal broadening provides detailed information about the annular mixing of the fuel and the pusher. This paper will compare the expected DT mix signals from capsules loaded with germanium to control capsules fired without any germanium. Leading turbulent mix models predict the germanium loaded capsules and no-germanium control capsules will produce significantly different results. [1] See Ryan Sacks ``Pushered single shell capsule design for the study of high Z mix on the National Ignition Facility'' this conference. [Preview Abstract] |
Tuesday, November 1, 2016 10:18AM - 10:30AM |
GO5.00005: Seeding of capsule instability growth by fill tubes and support rods for inertial confinement fusion implosions Andrew MacPhee, Daniel Casey, Daniel Clark, John Field, Steven Haan, Bruce Hammel, Jeremy Kroll, Otto Landen, David Martinez, Jose Milovich, Abbas Nikroo, Neal Rice, Harry Robey, Vladimir Smalyuk, Michael Stadermann, Christopher Weber Features associated with the target support tent and deuterium-tritium fuel fill tube and support rods can seed hydrodynamic instabilities leading to degraded performance for inertial confinement fusion (ICF) experiments at the National Ignition Facility. We performed in-flight radiography of ICF capsules in the vicinity of the capsule support tent and fill tube surrogates to investigate instability growth associated with these features. For both plastic and high density carbon ablators, the shadow of the 10$\mu $m diameter glass fill-tube cast by the x-ray spots on the hohlraum wall were observed to imprint radial instabilities around the fill tube/capsule interface. Similarly, instability growth was observed for the shadow cast by 12$\mu $m diameter silicon carbide capsule support rods mounted orthogonal to the fill tube as a tent alternative for a plastic ablator. The orientation of the shadows is consistent with raytracing. [Preview Abstract] |
Tuesday, November 1, 2016 10:30AM - 10:42AM |
GO5.00006: Polar tent for reduced perturbation of NIF ignition capsules B.A. Hammel, L. Pickworth, M. Stadermann, J. Field, H. Robey, H. A. Scott, V. Smalyuk In simulations, a tent that contacts the capsule near the poles and departs tangential to the capsule surface greatly reduces the capsule perturbation, and the resulting mass injected into the hot-spot, compared to current capsule support methods. Target fabrication appears feasible with a layered tent (43-nm polyimide $+$ 8-nm C) for increased stiffness. We are planning quantitative measurements of the resulting shell-$\rho $R perturbation near peak implosion velocity (PV) using enhanced self-emission backlighting, achieved by adding \textasciitilde 1{\%} Ar to the capsule fill in Symcaps ($^{\mathrm{4}}$He $+$ H). Layered DT implosions are also planned for an integrated test of capsule performance. We will describe the design and simulation predictions. [Preview Abstract] |
Tuesday, November 1, 2016 10:42AM - 10:54AM |
GO5.00007: Simulations of the impact of localized defects on ICF implosions Jose Milovich, Harry Robey, Christopher Weber, Scott Sepke, Daniel Clark, Joe Koning, Vladimir Smalyuk, David Martinez Recent experiments [1] have identified the tent membranes that support the capsule as a source of a large azimuthal perturbation at the point of departure from the surface. Highly-resolved 2D simulations have shown that vorticity generated by the interaction of the ablated capsule material and the tent allows for the penetration of cold ablator material into the burning hot-spot likely cooling the central burning plasma. These observations have motivated the search for alternative supporting methods. One of the techniques being considered uses the existing fill-tube (needed to deliver the cryogenic fuel) supported against gravity by a thin rod (cantilever) spanning the hohlraum diameter. Recent experiments have assessed the perturbation induced on the target as the rod is positioned along the fill-tube at different distances from the capsule surface and found optical-depth modulations oriented along the cantilever direction, possibly caused by laser spot shadowing or hydro-coupling. To fully understand the data we have undertaken an extensive study of highly-resolved 2D integrated simulations abled to resolve the 12 um diameter cantilever. Results of our computations and comparison with the experiments will be presented. [1] J. R. Rygg et al, Phys. Rev. Lett. 112, 195001 (2014) [Preview Abstract] |
Tuesday, November 1, 2016 10:54AM - 11:06AM |
GO5.00008: Stabilization of Thin-Shell Implosions Using a High-Foot Adiabat-Shaped Drive on the National Ignition Facility Marion Lafon, Pascal Gauthier, Laurent Masse The High Foot (HF) campaign on the National Ignition Facility (NIF) has improved the neutron yield by an order of magnitude as compared to the implosions reported during the National Ignition Campaign (NIC) while dramatically lowering the ablation-front instability growth. However, this yield increase came at the expense of reduced fuel compression due to higher fuel adiabat. Thinner shell adiabat-shaped HF implosions have been designed to combine the ablation front stability benefits of the current HF pulses with the demonstrated high fuel compressibility of the NIC implosions and increased implosion velocity. This is accomplished by using a hybrid adiabat-shaping technique which both lowers the laser power between the first and second pulses to enhance the ablative stabilization at early times and precisely tailors the rise-to-peak drive to prevent undesired shocks from propagating in the fuel and depositing additional entropy. Ablation front growth factor spectra are generated from two-dimensional simulations with the FCI2 radiation hydrodynamics code. Linear analysis of the instability growth demonstrates that adiabat-shaped pulses provide a path to control and reduce ablation front instability growth while placing the fuel on a lower adiabat to achieve the alpha-heating-dominated regime. Adiabat-shaped pulses without picket are also investigated as a potential way to enhance the stability of the holhraum walls at early times. [Preview Abstract] |
Tuesday, November 1, 2016 11:06AM - 11:18AM |
GO5.00009: Surface Roughness Instability Simulations of Inertial Confinement Fusion Implosions Kristopher McGlinchey, Nicolas Niasse, Jeremy Chittenden Understanding hydrodynamic instabilities seeded by the inherit roughness on a capsule's surface is critical in quantifying an implosion's performance. Combined with instabilities on the ice-gas interface during the deceleration phase, their growth can lead to inhomogeneity in the shell's areal density. Recent work carried out at the National Ignition Facility (NIF) on surface roughness Rayleigh-Taylor Instability (RTI) growth rates show larger amplitudes in experiment as compared to simulation, even with a deliberately roughened surface [1]. We report on simulations of ICF experiments occurring at NIF using the Chimera code developed at Imperial College. Chimera is a fully explicit, Eulerian 3D multi-group radiation-hydrodynamics code utilising P1/3 automatic flux limiting radiation transport with opacity data from a non-LTE atomic model also developed at Imperial College. One-dimensional simulations are briefly presented to highlight that proper shock timing and stagnation properties have been achieved as are 2D harmonic perturbation simulations to benchmark their growth rates. Surface roughness implosions (initialised from metrology data) were then simulated for: shot N120321, a low-foot implosion with large surface perturbations and shot N130927, a high-foot implosion. Synthetic radiographs of these implosions were constructed at low convergence ratio (3-4) for comparison to experiment and at higher convergence to investigate what will be observable by new diagnostics in development at NIF. [1] V.A. Smalyuk et al, High Power Laser Science and Engineering, 2015 [Preview Abstract] |
Tuesday, November 1, 2016 11:18AM - 11:30AM |
GO5.00010: Fuel areal density distributions derived from nuclear scattering signatures R. M. Bionta, D. T. Casey, C. J. Cerjan, C. B. Yeamans, M. G. Gatu Johnson The spatial variation of activities measured in the array of 20 Nuclear Activation Detectors mounted on the flanges around the NIF target chamber (FNADs) are correlated with asymmetries in the underlying fuel areal density of compressed ICF targets. The asymmetric areal density distributions cause variations in the neutron spectra with direction which are seen in the dsr (down scattered ratio) metric, the ratio of the number of 10-12 MeV neutrons to the number of 13-15 MeV neutrons. We show, using a simple physics based simulation of neutron scattering through an idealized non-uniform DT shell with a realistic neutron source, that for most shots an areal distribution can be found which reproduces both the FNAD activity and the dsr measurements. Furthermore, by linking the simulation to a Marquardt minimizer, we fit the areal distribution to a truncated set of spherical harmonics. [Preview Abstract] |
Tuesday, November 1, 2016 11:30AM - 11:42AM |
GO5.00011: Measurements of shock-front structure in multi-species plasmas on OMEGA Hans G. Rinderknecht, H.-S. Park, J. S. Ross, S. C. Wilks, P. A. Amendt, R. F. Heeter, J. Katz, N. M. Hoffman, E. Vold, W. Taitano, A. Simakov, L. Chacon The structure of a shock front in a plasma with multiple ion species is measured for the first time in experiments on the OMEGA laser. Thomson scattering of a 263.25~nm probe beam is used to diagnose electron density, electron and ion temperature, ion species concentration, and flow velocity in strong shocks ($M \sim 5$) propagating through low-density ($\rho \sim 0.1$~mg/cc) plasmas composed of H(98\%)+Ne(2\%) and H(98\%)+C(2\%). Separation of the ion species within the shock front is inferred. Although shocks play an important role in ICF and astrophysical plasmas, the intrinsically kinetic nature of the shock front indicates the need for experiments to benchmark hydrodynamic models. Comparison with PIC, Vlasov-Fokker-Planck, and multi-component hydrodynamic simulations will be presented. [Preview Abstract] |
Tuesday, November 1, 2016 11:42AM - 11:54AM |
GO5.00012: Asymptotic behavior of the mixed mass in Rayleigh-Taylor$^{\mathrm{\thinspace \thinspace \thinspace }}$and Richtmyer-Meshkov instability induced flows Ye Zhou, William Cabot, Ben Thornber Rayleigh-Taylor instability (RTI)$^{\mathrm{\thinspace }}$and Richtmyer-Meshkov instability (RMI) are serious practical issues in inertial confinement fusion (ICF) research and also have relevance to many cases of astrophysical fluid dynamics. So far much of the attention has been paid to the late-time scaling of the mixed width, which is used as a surrogate to how well the fluids have been mixed. Yet, the actual amount of mixed mass could be viewed as a more direct indicator on the evolution of the mixing layers due to hydrodynamic instabilities. Despite its importance, there is no systematic study as yet on the scaling of the mixed mass for either the RTI or the RMI induced flow. In this work, the normalized mixed mass ($\Psi )$ is introduced for measuring the efficiency of the mixed mass. Six large numerical simulation databases have been employed: the RTI cases with heavy-to-light fluid density ratios of 1.5, 3, and 9; the single shock RMI cases with density ratios of 3 and 20; and a reshock RMI case with density ratio of 3. Using simulated flow fields, the normalized mixed mass $\Psi $ is shown to be more sensitive in discriminating the variation with Atwood number for the RTI flows. Moreover, $\Psi $ is demonstrated to provide more consistent results for both the RTI and RMI flows when compared with the traditional mixedness parameters, $\Xi $ and $\Theta $. [Preview Abstract] |
Tuesday, November 1, 2016 11:54AM - 12:06PM |
GO5.00013: Hot spot model of MagLIF implosions: Nernst term effect on magnetic flux losses. Fernando Garcia Rubio, Javier Sanz Recio, Riccardo Betti An analytical model of a collisional plasma being compressed by a cylindrical liner is proposed and solved in a magnetized liner inertial fusion-like context. The implosion is assumed to be isobaric, and the magnetic diffusion is confined to a thin layer near the liner. Both unmagnetized and magnetized plasma cases are considered. The model reduces to a system of two partial differential equations for temperature and magnetic field. Special attention is given to the effect of the Nernst term on the evolution of the magnetic field. Scaling laws for temperature, magnetic field, hot spot mass increase and magnetic field losses are obtained. The temperature and magnetic field spatial profiles tend to a self-similar state. It is found that when the Nernst term is taken into account, the magnetic field is advected towards the liner, and the magnetic flux losses are independent of the magnetic Lewis number. [Preview Abstract] |
Tuesday, November 1, 2016 12:06PM - 12:18PM |
GO5.00014: Controlling Rayleigh-Taylor instabilities in solid liner implosions with rotating magnetic fields P. F. Schmit, R. D. McBride, G. K. Robertson, A. L. Velikovich We report calculations demonstrating that a remarkable reduction in the growth of the magneto-Rayleigh-Taylor instability (MRTI) in initially solid, cylindrical metal shells can be achieved by applying a magnetic drive with a tilted, dynamic polarization, forming a solid-liner dynamic screw pinch (SLDSP). Using a self-consistent analytic framework [A. L. Velikovich and P. F. Schmit, PoP 22, 122711 (2015)], we demonstrate that MRTI growth factors of the most detrimental modes may be reduced by up to two orders of magnitude relative to conventional z-pinch implosions. One key application of this technique is to enable increasingly stable, higher performance liner implosions to achieve fusion [M. R. Gomez et al., PRL 113, 155003 (2014)]. We weigh the potentially dramatic benefits of the SLDSP against the practical tradeoffs required to achieve the desired drive field history and identify promising target designs for future experimental and computational investigations. [Preview Abstract] |
Tuesday, November 1, 2016 12:18PM - 12:30PM |
GO5.00015: Development of the electrothermal instability from resistive inclusions Edmund Yu, T.J. Awe, B.S. Bauer, K.C. Yates, W.G. Yelton, T.M. Hutchinson, S Fuelling, B.B. Mckenzie, K.J. Peterson The magneto Rayleigh-Taylor (MRT) instability limits the performance of all magnetically imploded systems. In the case of compressing metal liners, as in the magnetized liner inertial fusion concept, a dominant seed for MRT is believed to be the electrothermal instability (ETI). Here, linear theory predicts the most unstable mode manifests as horizontal (i.e. perpendicular to current flow) bands of heated and expanded metal. However, how do such bands, known as striations, actually develop from a smooth metal surface? Recent experiments on ETI evolution, performed at the University of Nevada, Reno, provide a possible answer: pre-shot characterization of aluminum rods show numerous resistive inclusions, several microns in diameter and distributed throughout the rod. In this work, we use 3D MHD simulation and analytic theory to explore how current redistribution around these isolated inclusions, combined with ETI, can lead to rapid formation of the global striation structures. Later in time, striations expand and form density perturbations much larger than the initial inclusion size. [Preview Abstract] |
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