Bulletin of the American Physical Society
54th Annual Meeting of the APS Division of Plasma Physics
Volume 57, Number 12
Monday–Friday, October 29–November 2 2012; Providence, Rhode Island
Session PO4: National Ignition Facility Mix |
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Chair: John Kline, Los Alamos National Laboratory Room: 551AB |
Wednesday, October 31, 2012 2:00PM - 2:12PM |
PO4.00001: Initial results, emerging trends, and interpretations from the Mix Campaign on NIF Bruce Remington As part of the National Ignition Campaign (NIC), we are pursuing a series of experiments on the NIF to understand and minimize the effects of hydrodynamic mixing on capsule performance in cryogenic DT layered implosions. We are varying the capsule preheat shield dopants, ablator and fuel thicknesses, and laser drive. An overview of the Mix Campaign will be given, emerging trends pointed out, and analysis presented to illustrate the degree to which ablation-front Rayleigh-Taylor instability contributes to mixing of ablator material into the hot spot. [Preview Abstract] |
Wednesday, October 31, 2012 2:12PM - 2:24PM |
PO4.00002: Update on requirements and specifications for ignition experiments on NIF Steven Haan The National Ignition Campaign (NIC) on the National Ignition Facility plans to use an indirectly driven spherical implosion to assemble and ignite a mass of DT fuel. Requirements describing the specifics of the ignition implosion and the corresponding expected performance were established several years prior. These requirements include laser features, target fabrication and characterization, and data obtained from pre-ignition experiments. Since those requirements were originally set, the NIC has conducted a variety of experiments using surrogate targets, meant to define various aspects of the future ignition experiment. Results from this experimental campaign, as well as progress in understanding the laser performance and issues raised by target fabrication, have motivated updates to the target designs and pre-established requirements. A summary of these updates, and their implications for ignition campaign planning, will be presented. [Preview Abstract] |
Wednesday, October 31, 2012 2:24PM - 2:36PM |
PO4.00003: Layered capsule implosions at 500 TW on the National Ignition Facility Siegfried Glenzer We report on high-velocity implosions of inertial confinement fusion capsules filled with equimolar deuterium-tritium fuel. These experiments use more than 500 TW peak laser power and 1.8 MJ laser energy with the goal to observe signatures of alpha heating and significant 14.1 MeV fusion neutron yield. The experiments use 215 microns thick capsule ablators, 10{\%} thicker than used in previous experiments, to mitigate effects of Rayleigh-Taylor instability growth. In addition, the laser pulse shape has been selected to avoid conditions with high levels of hydrodynamic mix. Hot spot and fuel pressure and mix analysis will be presented to indicate proximity to the ignition regime within the pressure-temperature phase space. [Preview Abstract] |
Wednesday, October 31, 2012 2:36PM - 2:48PM |
PO4.00004: Measurements of the effects of mix on neutron yield and compression in layered capsule implosions on NIF V.A. Smalyuk, H.-S. Park, T. Doeppner, T. Ma, B.A. Remington, D. Callahan, B.A. Hammel, S.W. Haan, O.S. Jones, M.H. Key, N.B. Meezan, S.T. Prisbrey, S.V. Weber, S.H. Glenzer, J. Kline, J.A. Kyrala Recent layered capsule implosion experiments on the National Ignition Facility (NIF) included implosions driven with lower-power, longer pulse shapes. While some of these implosions produced higher compression, others produced higher fuel-ablator mix that can be inferred from the stagnation hotspot x-ray emission, neutron yield, and ion temperature. The connection between simulated perturbation growth and measured layered capsule performance, with focus on experimental observations, will be discussed. [Preview Abstract] |
Wednesday, October 31, 2012 2:48PM - 3:00PM |
PO4.00005: Predicting mix in NIF layered capsule implosions S.V. Weber, B.A. Remington, H.-S. Park, V.A. Smalyuk, D.S. Clark, B.A. Hammel, O.S. Jones, M.H. Key, N.B. Meezan, S.T. Prisbrey, B.K. Spears Layered capsule implosion experiments on the National Ignition Facility (NIF) in 2012 have sought to improve performance by varying capsule dopant fraction, ablator thickness, DT ice layer thickness, laser power rise rate, and peak laser power. Ablator mix into the hotspot, which can be inferred from the stagnation hotspot x-ray emission, neutron yield, and ion temperature, was seen to vary greatly. Simulated growth of perturbations on ablator and ice surfaces increases with increasing peak laser power and ablator dopant fraction and decreases with ablator and ice thickness. Simulated predictions and sensitivities, especially of ablator mix into the hot spot, will be compared to experimental results. [Preview Abstract] |
Wednesday, October 31, 2012 3:00PM - 3:12PM |
PO4.00006: Quantitative Measurements of Mix and Trends with Laser Power, Picket, and 4th Shock Rise Times in Cryogenic NIF Implosions T. Ma, N. Izumi, R. Tommasini, D.K. Bradley, C.J. Cerjan, T. Doeppner, M.J. Edwards, S.W. Haan, M.H. Key, J.L. Kline, A.J. Mackinnon, H.-S. Park, P.K. Patel, B.A. Remington, V.A. Smalyuk, P.T. Springer, R.P.J. Town, S.V. Weber, S.H. Glenzer Recent cryogenic deuterium-tritium (DT) capsule implosion experiments on the National Ignition Facility (NIF) have explored the effect of variations in laser pulseshape and power on mix of the ablator into the hot spot. Mix, generally due to hydrodynamic instabilities at the ablation front and at the fuel-ablator interface, can result in a reduced yield and ion temperature, and high x-ray brightness from the hot core due to the ablator mixing into the compressed fuel. Trends in the measured mix in the experimental data based on different laser drive power and pulse shapes (strength of the picket, rise time of the fourth pulse, and duration of the fourth pulse peak power) will be presented. A model that has been developed to quantify ablator mix into the hot spot based on absolute measured bremsstrahlung relative to the neutron yield will be discussed in detail. [Preview Abstract] |
Wednesday, October 31, 2012 3:12PM - 3:24PM |
PO4.00007: ABSTRACT WITHDRAWN |
Wednesday, October 31, 2012 3:24PM - 3:36PM |
PO4.00008: Spectroscopy of Mid-$Z$ Shell Additives in Implosions at the National Ignition Facility R. Epstein, S.P. Regan, R.L. McCrory, D.D. Meyerhofer, T.C. Sangster, B.A. Hammel, L.J. Suter, H. Scott, D.A. Callahan, C. Cerjan, N. Izumi, M.H. Key, O.L. Landen, N.B. Meezan, B.A. Remington, I.E. Golovkin, J.J. MacFarlane, R.C. Mancini, K.J. Peterson Ge and Cu dopants are added to CH ablators of NIF implosions to absorb x-ray preheat. K-shell spectral line emission from these dopants provides a core/shell-mix diagnostic.\footnote{S.P. Regan, ``Hot-Spot Mix and Compressed Ablator \textit{$\rho $R} Measurements in Ignition-Scale Implosions,'' this conference.} A model of the He-like line and satellite emission is fit to measured spectra to assay the mix mass. The underlying atomic model is appropriately complete for the anticipated temperature range, self-consistent with regard to radiation coupling, and detailed for the available spectral resolution. The high-temperature spectral components are fit well by the model, indicating low levels of hot-spot mix masses. Spectrally distinct satellite emission from lower-ionization species provides new measurements of doped shell material associated with mix close to the inner shell surface. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC52-08NA28302. [Preview Abstract] |
Wednesday, October 31, 2012 3:36PM - 3:48PM |
PO4.00009: Hot-Spot Mix and Compressed Ablator \textit{$\rho $R} Measurements in Ignition-Scale Implosions S.P. Regan, R. Epstein, D.D. Meyerhofer, T.C. Sangster, B.A. Hammel, L.J. Suter, J. Ralph, H. Scott, M.A. Barrios, D.K. Bradley, C. Cerjan, T. Doppner, S.H. Glenzer, S.W. Haan, O. Jones, O.L. Landen, H.S. Park, B.A. Remington, V.A. Smalyuk, P. Springer, J.D. Kilkenny, I.E. Golovkin, J.J. MacFarlane, J.L. Kline, R.C. Mancini Cu and Ge dopants placed at different radial locations in the plastic ablator of indirect-drive cryogenic DT implosions are used to study the origin of hot-spot mix via He$_{\alpha }$ + satellite emission spectroscopy, and to probe the compressed ablator \textit{$\rho $R} using K-edge absorption spectroscopy. Hot-spot mix is dominated by the ablation front instability. Low neutron yields correlate with hot-spot mix mass in excess of 75 ng. Hydrodynamic simulations of the implosion are consistent with the measured compressed ablator \textit{$\rho $R} of 0.35 to 0.5 g/cm$^{2}$. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC52-08NA28302. [Preview Abstract] |
Wednesday, October 31, 2012 3:48PM - 4:00PM |
PO4.00010: Using Symmetry Capsules to Study Ablation Front Rayleigh-Taylor Instability Growth in ICF Implosions Debra Callahan, Daniel Clark, Bruce Hammel, Denise Hinkel, Michael Key, Prav Patel, Stephen Weber, Laurent Masse Controlling Rayleigh-Taylor instability growth in ignition capsules involves trading-off growth at the ablation front with growth at the fuel-ablator interface. Mid-Z dopants, such as silicon or germanium, are added to the plastic ablator to prevent high energy x-rays from preheating the inside edge of the ablator causing an unfavorable Atwood number at the fuel-ablator interface. By controlling the dopant, this interface can be kept stable. The dopant, however, tends to cause a steeper ablation front, which results in more growth at the ablation front. Symmetry capsules, in which the fuel is replaced by an equivalent mass of additional plastic, have similar ablation front growth to an ignition capsule, but without the fuel-ablator instability. We will present neutron yield, ion temperature, x-ray yield data, and inferred mix from a variety of symmetry capsule experiments as we change dopant, capsule thickness, and laser power. [Preview Abstract] |
Wednesday, October 31, 2012 4:00PM - 4:12PM |
PO4.00011: Analyses of Cyrogenic Implosions at the National Ignition Facility D.E. Hinkel, D.S. Clark, D.C. Eder, O.S. Jones Cryogenic fuel layer experiments are currently underway at the National Ignition Facility (NIF). These experiments compress a $\sim $ 1mm sphere comprised of DT gas, frozen DT, and an ablator into a high density, cold shell that surrounds a low density hotspot where fusion is initiated. Accompanying experiments provide shock timing [1] and converging ablator [2] information about these implosions. Analyses use a tuned radiation source that is currently a best effort to match shock timing data, converging ablator data, bang time, and the fuel areal density [3]. These sources are used in multi-dimensional capsule simulations with representations of the as-shot ablator surface roughness and ice roughness, a representation of the largest groove present in the DT ice layer, the capsule tent, and radiation asymmetry. They are also used in growth factor simulations. Presented here is an example of a tuned radiation source, and subsequent results.\\[4pt] [1] T. R. Boehly \textit{et al}., Phys. Plasmas \textbf{18}, 092706 (2011)\\[0pt] [2] D. G. Hicks \textit{et al.}, Phys. Plasmas \textbf{17}, 102703 (2010).\\[0pt] [3] D. S. Clark, invited talk, this meeting. [Preview Abstract] |
Wednesday, October 31, 2012 4:12PM - 4:24PM |
PO4.00012: Hydra modeling of the effect of nearly complete inflight ice and ablator mix in a NIF implosion on several key diagnostics Andrea Kritcher, Scott Sepke, Howard Scott, Sean Regan, Laurent Masse, Kumar Raman, Gary Grim, Charlie Cerjan, Marty Marinak, Brian Spears, Nathan Meezan, Larry Suter A programmed mix model is used with the radiation hydrodynamics code HYDRA to explore the effects of nearly complete inflight mixing of the ice and ablator on NIC implosion performance and diagnostic signatures. In NIC DT implosions, nearly complete mix of the DT ice and ablator can be envisioned via cold jets of material penetrating the ice possibly combined with turbulence at the fuel-ablator interface. The quantitative impact of this scenario on several key NIF diagnostics, including yield, ion temperature, downscattered neutron spectrum, neutron imaging, Ge and Cu atomic emission analysis, gated x-ray imaging, and streaked x-ray radiography will be discussed. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. LLNL-ABS-564191. [Preview Abstract] |
Wednesday, October 31, 2012 4:24PM - 4:36PM |
PO4.00013: Altering the hydrodynamic mixing of NIF capsules with shocks and rarefactions J.L. Peterson, D.S. Clark, S.W. Haan, D.E. Hinkel, L.P. Masse, B.A. Remington, L.J. Suter Defects on inertial confinement fusion capsule surfaces can seed hydrodynamic instabilities, the growth of which can cause the mixing of fuel and ablator material and adversely affect capsule performance. Shocks and rarefactions during the early period of National Ignition Facility (NIF) implosions alter this mixing by determining whether perturbations will grow inward or outward at peak implosion velocity and final compression. Shocks can transport exterior defects to inner capsule surfaces and seed Richtmyer-Meshkov growth, while rarefactions can bring interior defects to outer surfaces such as the ablation front. These processes collectively determine the final seed on the ablation surface that grows exponentially during the main acceleration phase via the Rayleigh-Taylor instability. Through hydrodynamic simulations of multi-shock ignition designs and experiments, we examine how shocks, rarefactions, and capsule surfaces collectively alter the mixing of NIF capsules. [Preview Abstract] |
Wednesday, October 31, 2012 4:36PM - 4:48PM |
PO4.00014: Thermonuclear Yield Degradation Due to Low Mode Capsule Shape Asymmetries on NIF Inertial Fusion Implosions Robbie Scott, D.S. Clark, D.K. Bradley, D.A. Callahan, M.J. Edwards, S.W. Haan, M.M. Marinak, R.P.J. Town, P.A. Norreys, L.J. Suter The effects of Legendre polynomial $P_4$ capsule shapes on NIF inertial fusion implosions have been modelled using the radiation-hydrodynamics code Hydra. Large $P_4$ mode shapes cause regions of the hotspot/DT ice interface to become unstable during capsule deceleration, preventing stagnation; up to 50\% of the peak capsule kinetic energy remains unconverted to hotspot pressure, causing hotspot pressures to fall by up to $3.5\times$ and neutron yields to be reduced by up to $20\times$. Synthetic x-ray images show that positive $P_4$ amplitudes $>5\mu$ m are undetectable experimentally when using cryogenic DT capsules. Analysis of DHe$^3$ filled CH capsules and comparison with NIF experimental data indicate that the yield reduction for DT capsules with the same x-ray drive would be $\sim10-20\times$. The presence of undetectable $P_4$ modes would explain many characteristics of current NIF implosions including; large negative $P_2$ modes, the $\sim30\mu$ m hotspot size, the low inferred pressures and hotspot masses, and most importantly the $\sim10\times$ discrepancy between the measured capsule kinetic energy and the observed neutron yield. Experimental methods are proposed to infer the $P_4$ mode amplitude of DT capsules and then reduce this to ignition specification. [Preview Abstract] |
Wednesday, October 31, 2012 4:48PM - 5:00PM |
PO4.00015: Yield degradation by 3D asymmetries during the deceleration phase of ICF capsule implosions on the NIF Jeremy Chittenden, Shaun Taylor, Brian Appelbe, Nicholas Niasse We report on investigations into the effect of asymmetry on thermonuclear yield in ICF implosions on the NIF. Different forms of perturbation are applied to the full 3D volume of the DT fuel during the coast phase in order to stimulate the growth of Rayleigh-Taylor instabilities during the deceleration phase. Synthetic neutron spectra, radiography and soft X-ray images indicate that different forms of perturbation have characteristic diagnostic signatures which can provide clues as to the dominant source of asymmetry in experiments. A combination of high bandwidth multimode perturbations together with macroscopic asymmetries is found to give the best agreement with experiment. Scaling of the neutron yield and burn history with perturbation amplitude is discussed. Asymmetry at stagnation promotes the mixture of cold dense fuel with the hotspot and quenches the burn. 3D high bandwidth perturbations produce a series of narrow spikes of dense fuel which penetrate the hotspot and result in significantly more mix than axi-symmetric perturbations. The effect of non-uniformity in the rho-R of the main fuel upon alpha particle transport is evaluated using a kinetic model of alpha transport and heating. [Preview Abstract] |
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