Bulletin of the American Physical Society
57th Annual Meeting of the APS Division of Plasma Physics
Volume 60, Number 19
Monday–Friday, November 16–20, 2015; Savannah, Georgia
Session UO4: Inertial Confinement Fusion III |
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Chair: Brian Spears, Lawrence Livermore National Laboratory Room: 105/106 |
Thursday, November 19, 2015 2:00PM - 2:12PM |
UO4.00001: Role of shock-timing in two-shock platform Natalia Krasheninnikova, Paul Bradley, Rick Olson, George Kyrala, Bob Peterson, Barbara Devolder, Rahul Shah In present work we discuss the role of shock-timing and location of shock coalescence in newly developed two-shock platform on NIF. It is generally believed that single-shell capsules perform better when the shocks coalesce in the gas due to lower shell entropy, larger convergence ratio, better hot-spot assembly, and mix. Using HYDRA and RAGE with BHR we investigated this hypothesis for the case of separated reactants capsule and found when shocks coalesced in the gas yield improved by $\sim$ 50{\%} while acceptance energy only increased by $\sim$ 3{\%}. This suggests that improving shock timing can increase the neutron yield without a significant increase in the drive. The picture of how the mix changes with variation in shock timing is not as crisp as the overall performance. In particular, according RAGE with BHR, the mix mass can be higher or lower depending on the strength of the first shock, even when the location of coalescence is the same. However, DT yield, which is a measure of mix, noticeably increases when the shock coalesce in the gas due to prevalence of higher temperatures in the mixed region. So perhaps the mix mass is more sensitive to the strength of the shocks rather than the location of their coalescence. [Preview Abstract] |
Thursday, November 19, 2015 2:12PM - 2:24PM |
UO4.00002: Simulations of FY15 2-shock CH Campaign Shots Paul Bradley, R.R. Peterson, L. Yin, R.E. Olson, J.L. Kline, N.S. Krasheninnikova, S.A. MacLaren, T. Ma, J.D. Salmonson, G.A. Kyrala, J. Pino, E. Dewald, S. Khan, D. Sayre, R. Tommasini, J. Ralph, D. Turnbull The 2-shock campaign is a joint Los Alamos/Livermore project to investigate the role of shock timing, asymmetry, and shock convergence on the performance of ICF capsules. This campaign uses a simple two step pulse that makes it easier to correlate the effect of changing the laser pulse on the performance of the capsule. The $\sim$ 680 micron outer radius capsule has a CH or CH$+$1 at{\%} Si ablator approximately 175 microns thick surrounding the gas region that is either D$_{2}$ or THD gas at 0.0085 g/cc. The capsules are indirectly driven inside a gold hohlraum that is 9.2 mm long by 5.75 mm in diameter. The three CD inner surface capsules utilized THD fuel so that the DT yield would arise from mixing of CD shell material into the tritium of the gas region. Our simulated results compare well to the experimental yield, ion temperature, burn width, x-ray size, and radius versus time data. Work performed by Los Alamos National Laboratory under contract DE-AC52-06NA25396 for the National Nuclear Security Administration of the U.S. Department of Energy. [Preview Abstract] |
Thursday, November 19, 2015 2:24PM - 2:36PM |
UO4.00003: Alpha Heating and TN Burn in NIF Experiments Baolian Cheng, Thomas Kwan, Yi-Ming Wang, Frank Merrill, Charlie Cerjan, Steven Batha Sustainable TN burn requires alpha-particle energy deposition in the hot fuel. Recently, we developed an analytic model to estimate the neutron yield generated by the alpha-particle energy deposited in the hot spot, in terms of the measured total neutron yield, the adiabat of the cold fuel and the peak implosion kinetic energy of the pusher [1]. Our alpha heating model has been applied to a number of inertial confinement fusion capsule experiments performed at the National Ignition Facility (NIF). Our model predictions are consistent with the post-shot calibrated code simulations and experimental data. We have also studied the uncertainty and sensitivities of alpha heating on various physics parameters, such as the adiabat of cold fuel, total neutron yield and peak implosion velocity. Our analysis demonstrates that the alpha particle heating was appreciable in only high-foot experiments. Based on our work, we will discuss paths and parameters to reach ignition at NIF (LA-UR-15-25507). This work was performed under the auspices of the U.S. Department of Energy by the Los Alamos National Laboratory under Contract No. W-7405-ENG-36. \\[4pt] [1] B. Cheng, T.J.T. Kwan, Y.M. Wang, F. Merrill, C. Cerjan, and S.H. Batha, accepted by Phys. Plasma, 2015. [Preview Abstract] |
Thursday, November 19, 2015 2:36PM - 2:48PM |
UO4.00004: Framed X-Ray Imaging of Cryogenic Target Implosion Cores on Omega F.J. Marshall, V.N. Goncharov, V.Yu. Glebov, S.P. Regan, T.C. Sangster, C. Stoeckl Cryogenic DT target implosions being performed on the OMEGA Laser System are now being diagnosed by two high-speed x-ray framing cameras ($\sim 30\mbox{-ps}$ frame times) able to time- and space-resolve the evolving high-pressure stagnating plasma core. One high-speed framing camera is coupled to a pinhole array and is able to image the core emission every 15 ps with $\sim 16\mbox{-}\mu \mbox{m}$ spatial resolution. It can accurately measure the time of x-ray emission peak and duration. The other framing camera is coupled to a novel 16-image Kirkpatrick--Baez (KB)-type x-ray optic\footnote{ F. J. Marshall, Rev. Sci. Instrum. \textbf{83}, 10E518 (2012).} providing $\sim 7\mbox{-}\mu \mbox{m}$ spatial resolution and can also sample the emission with images spaced in time by as little as $\sim$ 15 ps. The core emission size determined from the framed KB images at the peak of stagnation allows for inferences of core pressure when combined with measurements of the ion temperature, burnwidth, and neutron yield. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. [Preview Abstract] |
Thursday, November 19, 2015 2:48PM - 3:00PM |
UO4.00005: Cross-Beam Energy Transfer Mitigation in Cryogenic Implosions on OMEGA V.N. Goncharov, S.P. Regan, T.C. Sangster, R. Betti, T.R. Boehly, D.H. Edgell, R. Epstein, C.J. Forrest, D.H. Froula, V.Yu. Glebov, S.X. Hu, I.V. Igumenshchev, J.A. Marozas, F.J. Marshall, R.L. McCrory, D.D. Meyerhofer, D.T. Michel, J.F. Myatt, P.B. Radha, W. Seka, A. Shvydky, C. Stoeckl, W. Theobald, B. Yaakobi, M. Gatu Johnson The OMEGA Laser System is used to study the physics of cryogenic implosions that are hydrodynamically equivalent to the spherical ignition designs of the National Ignition Facility. Based on these experiments, cross-beam energy transfer (CBET) has been identified as the main mechanism reducing laser coupling and hydroefficiency. To mitigate CBET, target size $R_{\mathrm{t}}$ was increased with respect to the size of the beam focal spot $R_{\mathrm{b}}$. This increases drive pressure, allowing for a thicker, more-stable target to reach ignition-relevant implosion velocities. The beam shape was optimized to minimize the nonuniformity produced when $R_{\mathrm{b}}$/$R_{\mathrm{t}}$ \textless 1. This talk will summarize the latest results in direct-drive implosions with different $R_{\mathrm{b}}$/$R_{\mathrm{t}}$. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. [Preview Abstract] |
Thursday, November 19, 2015 3:00PM - 3:12PM |
UO4.00006: Impact of low-mode asymmetry on the integrity of stagnation phase N. Izumi, B.K. Spears, D.C. Eder, A.E. Pak, J.J. Ruby, C.B. Yeamans, R. Hatarik, S.W. Haan, D.A. Callahan, O.A. Hurricane, D.K. Bradley, D.T. Casey In inertial confinement fusion experiments, kinetic energy of the accelerated shell is converted to the internal energy of the low density core. If an implosion is not uniform enough (in terms of shape, mass, or velocity), the efficiency of the conversion is degraded and a significant fraction of the energy stays as kinetic energy of the fluid motion. Experimentally, it is possible to infer the speed of the fluid motion from the Doppler shift and broadening of the neutrons produced in the burning region [1,2]. In the case of recent ``high-foot'' shots, the neutron time-of-flight diagnostics are indicating the existence of substantial residual fluid motion. To maximize the efficiency of the conversion, it is important to quantify how the perturbation given to x-ray drive or capsule shape affects the efficiency of the conversion. We carried out implosion experiments with an imposed low mode asymmetry (to the x-ray drive and the ice layer thickness) and measured how the given perturbation affects the core performance (neutron yield, areal density). The results of the experiment and the comparison to hydrodynamic simulations will be reported. \\[4pt] [1] M. Gatu Johnson, et al., Phys. Plas. 20, 042707 (2013)\\[0pt] [2] B. Spears, et al., Rhys. Plas 21. 042702 (2014). [Preview Abstract] |
Thursday, November 19, 2015 3:12PM - 3:24PM |
UO4.00007: The effect of hohlraum drive asymmetry on the observed in-flight momentum and hot spot emission non-uniformity in ICF implosions Arthur Pak, J.E. Field, A. Kritcher, R. Nora, L.F. Berzak Hopkins, L. Divol, S.F. Khan, T. Ma, R. Tommasini, D.K. Bradley, D. Callahan, D. Hinkel, O.A. Hurricane, O.S. Jones, A.J. Mackinnon, S.A. MacLaren, N.B. Meezan, J. Moody, P. Patel, H.F. Robey, V.A. Smalyuk, B.K. Spears, R.P.J. Town, M.J. Edwards At the National Ignition Facility indirectly driven inertial confinement fusion experiments are being conducted. In order to maximize the efficiency at which kinetic energy of the capsule ablator and fuel is converted to internal hot spot energy, asymmetries in the shape of the ablator and fuel momentum must be minimized. In this work an overview across different implosion experiments detailing the observed relationship between the in-flight ablator momentum symmetry and factors that modify the hohlraum radiation flux symmetry such as the density of the hohlraum gas fill, laser wavelength separation, and case to capsule ratio will be given. A measurement of the ablator momentum asymmetry at peak velocity can be made using the two-dimensional radiographs of the capsule ablator taken in-flight, at radii of 300 to 200 \textunderscore m. Additionally the relationship between the morphology of the observed in-flight ablator and the x-ray self emission at stagnation will be examined. 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] |
Thursday, November 19, 2015 3:24PM - 3:36PM |
UO4.00008: A 3-D Model of Hot-Spot Formation in Inertial Confinement Fusion Implosions X. Gong, V.N. Goncharov, I.V. Igumenshchev A 3-D model describing the formation of a hot-spot in inertial confinement fusion (ICF) implosions is presented. The model includes thermal conduction and mass ablation effects in a 3-D distorted hot spot using an approach developed by Sanz.\footnote{J. Sanz and R. Betti, Phys. Plasmas \textbf{12}, 042704 (2005).} Evolution of the nonuniformity growth is calculated based on a sharp boundary model.\footnote{V. N. Goncharov \textit{et al}., Phys. Plasmas \textbf{7}, 5118 (2000).} The results of the model will be compared against 2-D \textit{DRACO} and 3-D hydrodynamic code calculations.\footnote{ I. V. Igumenshchev \textit{et al}., ``Numerical Study of Large-Scale, Laser-Induced Nonuniformities in Cryogenic OMEGA Implosions,'' this conference.} This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. [Preview Abstract] |
Thursday, November 19, 2015 3:36PM - 3:48PM |
UO4.00009: Hot spot temperature measurements in DT layered implosions Pravesh Patel, T. Ma, A. MacPhee, D. Callahan, H. Chen, C. Cerjan, D. Clark, D. Edgell, O. Hurricane, N. Izumi, S. Khan, L. Jarrott, A. Kritcher, P. Springer The temperature of the burning DT hot spot in an ICF implosion is a crucial parameter in understanding the thermodynamic conditions of the fuel at stagnation and and the performance of the implosion in terms of alpha-particle self-heating and energy balance. The continuum radiation spectrum emitted from the hot spot provides an accurate measure of the emissivity-weighted electron temperature. Absolute measurements of the emitted radiation are made with several independent instruments including spatially-resolved broadband imagers, and space- and time-integrated monochromatic detectors. We present estimates of the electron temperature in DT layered implosions derived from the radiation spectrum most consistent with the available measurements. The emissivity-weighted electron temperatures are compared to the neutron-averaged apparent ion temperatures inferred from neutron time-of-flight detectors. 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] |
Thursday, November 19, 2015 3:48PM - 4:00PM |
UO4.00010: Measurement of the hot spot electron temperature in NIF ICF implosions using Krypton x-ray emission spectroscopy T. Ma, H. Chen, P.K. Patel, M. Schneider, M. Barrios, L. Berzak Hopkins, D. Casey, H.-K. Chung, B. Hammel, C. Jarrott, R. Nora, A. Pak, H. Scott, B. Spears, C. Weber The inference of ion temperature from neutron spectral measurements in indirect-drive ICF implosions is known to be sensitive to non-thermal velocity distributions in the fuel. The electron temperature (Te) inferred from dopant line ratios should not be sensitive to these bulk motions and hence may be a better measure of the thermal temperature of the hot spot. Here we describe a series of experiments to be conducted on the NIF where a small concentration of a mid-Z dopant (Krypton) is added to the fuel gas. The x-ray spectra is measured and the electron temperature is inferred from Kr line ratios. We also quantify the level of radiative cooling in the hot spot due to this mid-Z dopant. These experiments represent the first direct measurement of hot spot Te using spectroscopy, and we will describe the considerations for applying x-ray spectroscopy in such dense and non-uniform hot spots. This work performed under the auspices of U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. [Preview Abstract] |
Thursday, November 19, 2015 4:00PM - 4:12PM |
UO4.00011: Inferring the time resolved core electron temperature from x-ray emission measured by a streak camera Shahab Khan, Pravesh Patel, Nobuhiko Izumi, Andrew G. MacPhee, Tammy Ma, Charlie Cerjan, David K. Bradley The electron temperature (T$_{\mathrm{e}})$ of the hot spot within the core of imploded inertial confinement fusion capsules is an effective indicator of implosion performance. A temporally resolved measurement of T$_{\mathrm{e}}$ helps elucidate the mechanisms for hot spot heating and cooling such as alpha-heating and mix. Additionally, comparison with simulations will aid in tuning models to effectively predict implosion performance. The Streaked Polar Instrumentation for Diagnosing Energetic Radiation (SPIDER) is an x-ray streak camera designed to record the x-ray burn history during the stagnation phase. SPIDER accurately reports bang time and burn duration of implosions on the National Ignition Facility (NIF). The addition of several filters of specific materials and thicknesses spread across the spatial axis of the streak camera imager allows for a least square fit of the signal through these filters to a bremsstrahlung hot spot model. The fitted parameters of the model are the T$_{\mathrm{e}}$, opacity, and X-ray yield which is valuable for ablator mix estimates. The details of this calculation and results from several shots on NIF are presented. [Preview Abstract] |
Thursday, November 19, 2015 4:12PM - 4:24PM |
UO4.00012: Hot Spot Electron Temperature from X-Ray Continuum Measurements on the NIF Leonard Jarrott, Hui Chen, Nobuhiko Izumi, Shahab Khan, Tammy Ma, Sabrina Nagel, Arthur Pak, Pravesh Patel, Marilyn Schneider, Howard Scott We report on direct measurements of the electron temperature within the hot spot of inertially confined, layered, spherical implosions on the National Ignition Facility using a new differential filtering diagnostic. Measurements of the DT and DD ion temperatures using neutron time-of-flight detectors are complicated by the contribution of hot spot motion to the peak width, which may produce an apparent temperature higher than the thermal temperature. The electron temperature is not sensitive to this non-thermal velocity and is thus a valuable input to interpreting the stagnated hot spot conditions. Here we discuss a new electron temperature measurement using the high energy (\textgreater 15 keV) emitted continuum from the hotspot that can escape with minimal attenuation from the compressed fuel/shell. We will discuss the physics considerations for design of this new large-pinhole, hard x-ray imaging technique, and show preliminary data acquired from symcaps and DT-layered implosions. Validation of this technique against simulations and other diagnostics is performed to estimate the accuracy of the measurement. [Preview Abstract] |
Thursday, November 19, 2015 4:24PM - 4:36PM |
UO4.00013: Characterizing Hot-Spot Dynamics of Direct-Drive Cryogenic Implosions on OMEGA K.S. Anderson, P.W. McKenty, A. Shvydky, J.P. Knauer, T.J.B. Collins, J.A. Delettrez, D. Keller, M.M. Marinak In direct-drive inertial confinement fusion, nonuniformities in laser drive, capsule manufacture, and target positioning lead to non-radial hydrodynamic flow in the hot spot at stagnation. Characterizing such flow in the hot spot requires simulating the entire capsule in three dimensions to remove symmetry boundary conditions, which artificially constrain hot-spot flow. This paper will present results from 3-D simulations of cryogenic implosions on OMEGA using \textit{HYDRA}. Low-mode asymmetries and their contributions to residual hot-spot kinetic energy will be discussed. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944 and performed under the auspices of LLNL under Contract No. DE-AC52-07NA27344. [Preview Abstract] |
Thursday, November 19, 2015 4:36PM - 4:48PM |
UO4.00014: X-ray Imaging of MagLIF Experiments Using a Spherically-Bent Crystal Optic E.C. Harding, M.R. Gomez, C.A. Jennings, P.F. Knapp, S.A. Slutz, A.B. Sefkow, T.J. Awe, S.B. Hansen, K.J. Peterson, K.D. Hahn, R.D. McBride, G.A. Rochau, D.B. Sinars, I. Golovkin The recent Magnetized Liner Inertial Fusion (MagLIF) experiments performed on Sandia's Z-machine produced significant thermonuclear DD fusion yields that were accompanied by observable x-ray emission [M.R. Gomez \textit{et. al.,} PRL (2014)]. The MagLIF experiments relied on a spherically-bent crystal optic to image portions of the x-ray continuum that were generated by the hot stagnation plasma. The images of stagnation show a long (6 to 8 mm) and narrow ($\sim $100 micron) column of x-ray emission with structure in both directions. This structure may be caused by variations in the electron temperature (T$_{\mathrm{e}})$ and density (n$_{\mathrm{e}})$, as well as opacity variations in the surrounding Be pusher. Here we investigate the possible contributions from each of these effects. We will also discuss the development of a diagnostic technique in which T$_{\mathrm{e}}$ and n$_{\mathrm{e}}$ of the DD fuel are inferred from spectra emitted by Fe impurities that become ionized to a He-like charge state. [Preview Abstract] |
Thursday, November 19, 2015 4:48PM - 5:00PM |
UO4.00015: Numerical Study of Large-Scale, Laser-Induced Nonuniformities in Cryogenic OMEGA Implosions I.V. Igumenshchev, V.N. Goncharov, F.J. Marshall, K. Silverstein, J.P. Knauer, D.H. Froula, S.P. Regan Performance of direct-drive implosion targets on OMEGA can suffer from large-scale laser-induced nonuniformities with L-modes less than about 10. These nonuniformities develop because of a discrete illumination of targets with the 60 OMEGA laser beams and because of imperfect pointing, profile shaping, energy balance, and timing of these beams. In addition, a significant nonuniformity with $\ell =1$ can result from an unintentional offset (typically $\sim$10 $\mu$m) of targets with respect to the laser beam pointing center. Effects of all these nonuniformities on the evolution of cryogenic implosion targets are studied numerically using 3-D hydrodynamic simulations. Nonuniformities that affect mostly the implosion performance are identified and limits on their magnitude are suggested basing on the results of simulations. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. [Preview Abstract] |
Thursday, November 19, 2015 5:00PM - 5:12PM |
UO4.00016: Time history and performances of direct-drive implosion on the Omega facility Stephane Laffite, Jean-Luc Bourgade, Tony Caillaud, Frederic Girard, Olivier Landoas, Sebastien Lemaire, Laurent Masse, Paul-Edouard Masson-Laborde, Frank Philippe, Charles Reverdin, Veronique Tassin, Guillaume Legay, Jacques Delettrez, Vladimir Glebov, Frederic Marshall, Tomline Michel, Wolf Seka, Tirtha Joshi, Roberto Mancini, Johan Frenje We present direct-drive experiments which were carried out on the Omega facility. Three different pulse shapes were tested in order to vary the implosion stability of the same target. The direct-drive configuration on the Omega facility allows the accurate time-resolved measurements of the scattered light. We show that, providing the laser coupling is well controlled, the implosion time history, assessed by the ``bang-time'' and the shell trajectory measurements, can be predicted. This conclusion is independent on the pulse shape. On the contrary, we show that the pulse shape affects the implosion stability, assesses by the comparison of the target performances, between prediction and measure. For the 1-ns square pulse, the measured neutron number is about 80{\%} of the prediction. For the 2-step 2-ns pulse, this ratio falls down to about 20{\%}. [Preview Abstract] |
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