Bulletin of the American Physical Society
55th Annual Meeting of the APS Division of Plasma Physics
Volume 58, Number 16
Monday–Friday, November 11–15, 2013; Denver, Colorado
Session JO7: Inertial Confinement Fusion |
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Chair: Daniel Clark, Lawrence Livermore National Laboratory Room: Governor's Square 12 |
Tuesday, November 12, 2013 2:00PM - 2:12PM |
JO7.00001: Update to Rev6 ignition designs NIF, with details about support tent in particular S.W. Haan, L. Berzak Hopkins, D.S. Clark, D. Eder, B.A. Hammel, A. Hamza, D. Ho, O.S. Jones, A. Kritcher, K. LaFortune, B.J. MacGowan, N.B. Meezan, J. Milovich, J.L. Peterson, H.F. Robey, J.D. Salmonson, B.K. Spears, R.P. Town, J.L. Kline, D.C. Wilson, A.N. Simakov, S.A. Yi, A. Nikroo, H. Huang, D. Hoover Ignition experiments on the National Ignition Facility will use an indirectly driven spherical implosion to assemble and ignite a mass of DT fuel. Requirements describing the specifics of the experiment 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, various NIF experiments using surrogate targets have motivated updates to the target designs and requirements. A summary of these updates will be presented. Rev6 designs for CH(Si), C(W), and Be(Cu) will be summarized. One particularly significant change regards the thickness of the tent films supporting the capsule, and the presentation will include updated thickness goals and the experimental motivation for the change. Prepared by LLNL under Contract DE-AC52-07NA27344. [Preview Abstract] |
Tuesday, November 12, 2013 2:12PM - 2:24PM |
JO7.00002: High-Density Carbon Ablator Experiments on the National Ignition Facility James Ross, Andrew MacPhee, James McNaney, Tilo Doeppner, Art Pak, Ryan Rygg, Robin Benedetti, Richard Town, David Bradley, Edward Dewald, Ricardo Tommasini, Jose Milovich, Laura Berzak-Hopkins, John Moody, Debbi Callahan, Alex Hamza, Juergen Biener, Darwin Ho, Eric Storm, Joe Kilkenny, Otto Landen, John Lindl, John Edwards, Nathan Meezan, Andrew Mackinno A series of experiments on the National Ignition Facility (NIF) have been preformed to measure high-density carbon (HDC) ablator performance for indirect drive inertial confinement fusion (ICF). The NIF laser was used to generate a shaped laser pulse with a peak power of 360 TW and a total energy of 1.3 MJ. The total neutron yield, ion temperature, neutron bang time and x-ray bang time were measured and compared to simulations. A deuterium-tritium filled HDC capsule recently produced a neutron yield of 1.6x10$^{\mathrm{15}}$, the current record for laser driven ICF. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and supported by LDRD-11-ERD-075. [Preview Abstract] |
Tuesday, November 12, 2013 2:24PM - 2:36PM |
JO7.00003: Ignition relevant ablator response of boron carbide and high-density carbon driven by multiple shocks Shon T. Prisbrey, Kevin Baker, Peter Celliers, Tom Dittrich, Alastair Moore, Kuang Jen Wu, Peggy Kervin, Omar Hurricane The attainment of self-propagating fusion burn in an inertial confinement target at the National Ignition Facility will require the use of an ablator with high rocket-efficiency and ablation pressure. The current ablation material, a glow-discharge polymer (GDP), does not couple as efficiently as simulations indicated to the multiple-shock inducing radiation drive environment created by laser power profile. In an effort to evaluate the performance of other possible ablators that could be suitable for achieving self-propagating fusion burn we have inferred the ablation performance of two possible ablators, boron carbide and high-density carbon, by measuring the shock speed of induced shocks while subjecting the ablators to a multiple-shock inducing radiation drive environment similar to a generic three-shock ignition drive. We present the platform used, velocity measurements used to infer the ablation response, and matching simulations to show the relative performance of boron carbide and high-density carbon with a general comparison to current performance of the currently used glow-discharge polymer ablator. [Preview Abstract] |
Tuesday, November 12, 2013 2:36PM - 2:48PM |
JO7.00004: Design of a two shock, high yield high-density carbon NIF target L. Berzak Hopkins, D. Callahan, L. Divol, J. Edwards, S. Haan, D. Ho, S. Le Pape, J. Lindl, A. Mackinnon, N. Meezan, J. Milovich, S. Ross, H. Robey, M. Rosen, E. Storm In 2013, the first indirect drive exploding pusher (IDEP) targets were fielded on the NIF. These targets utilized a near-vacuum hohlraum (16 torr of helium) and thin (120 $\mu $m) GDP capsule with a short (4.5 ns) single shock drive. With long pulses, a hohlraum gas fill is typically needed to achieve symmetry. The short pulse of the IDEP permitted the usage of a near-vacuum hohlraum, which served to minimize laser-plasma interactions, such as cross beam transfer and backscatter, and achieved 99{\%} laser-hohlraum coupling. Both deuterium-deuterium and deuterium-tritium filled capsules produced high yields (approximately 5 x 10$^{\mathrm{12}}$ and 5 x 10$^{\mathrm{14}}$ neutrons, respectively) and were predicted well by HYDRA simulations with un-degraded laser drive. In addition, new experiments fielding high-density carbon (HDC) capsules in standard, gas-filled hohlraums have achieved the highest NIF neutron yields to-date. Combining and building upon these results, a two shock drive in a near-vacuum hohlraum with an HDC capsule has been developed. Challenges of the near-vacuum hohlraum, design of the two shock system, and first results will be discussed. [Preview Abstract] |
Tuesday, November 12, 2013 2:48PM - 3:00PM |
JO7.00005: Single shock implosion on the NIF Sebastein le Pape, Laurent Divol, Laura Berzak Hopkins, Dan Casey, Alex Zylstra, Mike Rosenberg, Maria Gatu Johnson, Johan Frenje, Richard Bionta, Jim Macnaney, Bob Kauffman, Joe Kilkenny, John Lindl, Warren Hsing, John Edwards, Richard Petrasso, Nathan Meezan, Andrew Mackinnon The indirect Drive Exploding Pusher (IDEP) is a new experimental platform fielded on the National Ignition Facility to study capsule hydrodynamic performance. A vacuum hohlraum and one color laser power are used to minimize the laser-plasma interaction uncertainty due to cross beam energy transfer, while symmetry of the implosion is achieved through direct power balance between the inner and outer cones. A single shock is launched into a 120 $\mu$m thick CH capsule filled with DD or DT gas. The capsule thickness and hohlraum drive are designed so that the ablator explodes in flight and has a low convergence factor ($\sim$ 5). The neutron yield is then dominated by the shock flash/free fall yield before ablator material can mix into the fuel. On the first experiment using a DD fill, the measured laser to hohlraum coupling was 99{\%}, and the measured neutron yield came within 15{\%} of the yield predicted by simulations using an undegraded drive. Results and hydrodynamic simulations of this new experimental platform will be presented. This work was performed under the auspices of the U.S. Department of Energy by the Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344. [Preview Abstract] |
Tuesday, November 12, 2013 3:00PM - 3:12PM |
JO7.00006: Shock timing measurements in DT ice layers H.F. Robey, P.M. Celliers, J.D. Moody, J. Sater, T. Parham, B. Kozioziemski, R.J. Dylla-Spears, J.S. Ross, S. LePape, J.E. Ralph, L.F. Berzak Hopkins, J.J. Kroll, B.E. Yoxall, A.V. Hamza, T.R. Boehly, A. Nikroo, O.L. Landen, M.J. Edwards Shock timing experiments on the National Ignition Facility (NIF) are routinely conducted using the keyhole target geometry, in which the strength and timing of multiple shocks are measured in a liquid-deuterium (D2) filled capsule interior. These targets have recently been modified to improve the surrogacy to ignition implosions by replacing the standard, continuous liquid D2 capsule fill with a deuterium-tritium (DT) ice layer with a central DT gas fill. These experiments remove any possible material surrogacy difference between D2 and DT as well as incorporating the physics of multiple shock release and recompression events from an ice layer of finite thickness, an effect that is absent in the liquid-filled targets. Experimental results and comparisons with numerical simulation are presented. [Preview Abstract] |
Tuesday, November 12, 2013 3:12PM - 3:24PM |
JO7.00007: Tracking the movement of the ICF hot spot using the time variance of the shape measured with gated x-ray cameras at NIF Shahab Khan, Brian Spears, Arthur Pak, Laura Benedetti, Tammy Ma, Nobuhiko Izumi, Luc Peterson, Oggie Jones, Richard Town, Dave Bradley The requirements for a successful Inertial Confinement Fusion (ICF) implosion include an efficient coupling of the drive to the inward implosion of the capsule as well as a near symmetric convergence of the capsule during and after the drive. In order to maximize coupling efficiency, the drive should be such as to minimize the translation of the capsule's center of mass during the implosion. This study will focus on the methods utilized to measure capsule movement. The National Ignition Facility (NIF) employs gated x-ray framing cameras to capture snapshots of the x-ray hot spot or backlit images of the shell during implosion. Ideally, the movement of the capsule would be measured by the position of the image on the detector. However, this does not give accurate results because the registration of the pinholes to the detector is not known and the distance between the pinholes are irregular. An indirect method is to track the center of nested contours of the images as a function of time. An assessment of these methods on several shots, including one with an imposed asymmetric drive, is presented. [Preview Abstract] |
Tuesday, November 12, 2013 3:24PM - 3:36PM |
JO7.00008: The effects of 3D asymmetries in ICF capsule implosions on the National Ignition Facility 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. 3D radiation hydrodynamics calculations of the entire capsule volume are presented which attempt to predict the structural form of the perturbations at the stagnation phase, based upon initial capsule defects, dust particles, radiation drive asymmetries, etc. Asymmetries arising at the interface between the hotspot and the cold dense fuel layer are further amplified by the Rayleigh-Taylor instability during the deceleration phase. Where multi-mode asymmetries interact in three dimensions, not all of kinetic energy is dissipated effectively. Low mode asymmetries which change the overall shape of the hotspot increase the surface area leading to increased thermal conduction. Higher mode asymmetries promote mixing of the cold fuel layer into the hotspot at stagnation. This essentially acts as an increased rate of ablation of the dense fuel at the hotspot surface, pulling material with low specific enthalpy into the hotpot, lowering the average hotspot temperature and quenching the burn. Signatures of the form of the perturbations are revealed in synthetic neutron spectra, X-ray images and radiography data. [Preview Abstract] |
Tuesday, November 12, 2013 3:36PM - 3:48PM |
JO7.00009: Integrated P1 Hohlraum/Capsule Simulations with Comparison to Neutron and X-Ray Measurements D.C. Eder, B.K. Spears, R.P. Town, O.S. Jones, D.H. Munro, J.L. Peterson, T. Ma, A.K. Pak, L.R. Benedetti, S.P. Hatchett, J.P. Knauer, A.J. MacKinnon, C.B. Yeamans, J.M. McNaney, D.T. Casey We discuss integrated hohlraum/capsule simulations that drive a DT symcap capsule downward in a NIF experiment by increasing/decreasing the peak power in the upper/lower laser beams by 8{\%}. This laser asymmetry results in a radiation drive P1/P0 at the capsule ablation surface of 2{\%} and a downward capsule velocity of 125 microns/ns. The simulation shows small (\textless 1{\%}) changes in the P2 and P4 moments of the x-ray self-emission as compared to a simulation with no laser asymmetry. The calculated reduction in yield due to the induced P1 is 20{\%}. Simulations for DT layered capsules for comparable velocities have yields an order of magnitude lower than simulations with stationary capsules. The velocity is measured by comparing the arrival times of DD and DT neutrons at detectors located at different locations. Preliminary data from a recent shot gives a downward velocity of order 100 microns/ns consistent with simulations. We also compare pre- and post-shot simulations with x-ray images at different energies. The ability to correct for capsule velocity, e.g., due to different upper/lower crossbeam transfer energies, is another tool in the quest for ignition. [Preview Abstract] |
Tuesday, November 12, 2013 3:48PM - 4:00PM |
JO7.00010: Tuning the early-time radiation flux symmetry in indirect drive implosion experiments at the National Ignition Facility Arthur Pak, Edward Dewald, Jose Milovich, Steve Glenn, Pierre Michel, Otto Landen, Richard Town, David Bradley At the National Ignition Facility, experiments to enhance the implosion performance by changing the hohlraum length, implosion adiabat and ablator material have been conducted. For each experiment the uniformity of the x-ray radiation flux at the capsule surface is crucial for ensuring a symmetric compression of the fusion target capsule. Of particular importance is the early-time symmetry of the x-ray radiation flux created by the first pulse or picket of the laser. Asymmetries in the early-time radiation flux can lead to uncorrectable asymmetries in the fuel assembly and hot spot shape that can degrade implosion performance. This work will describe the changes to the early-time radiation flux and detail the tuning necessary to ensure a symmetric early-time radiation flux at the capsule surface as the hohlraum length, implosion adiabat and ablator material are changed. Results from reemission experiments conducted to tune the symmetry in 10.13 mm long hohlraums, implosions with an adiabat of $\sim$2.8 and capsules with high density carbon ablator material will be presented and compared to results from three dimensional radiation hydrodynamic calculations. [Preview Abstract] |
Tuesday, November 12, 2013 4:00PM - 4:12PM |
JO7.00011: Effect of High-Z Doping on ICF TN Performance and Ignition Yi-Ming Wang One of the challenges of ICF ignition is to achieve desired areal density $\rho $R of the hot-spot region so that a self-sustained TN burn could be initiated and maintained. The recent study of the NIC data indicated that the areal density $\rho $R of the hot-spot inferred by the DSR was lower than the ignition requirement set by ITF. In this work, we will study the effect of Hi-Z doping in the DT gas on the ICF TN performance. The mechanism of the high-Z doping is to utilize additional radiative cooling of high-Z doping during the implosion phase of the evolution so that the gas cavity will follow a lower adiabatic path. This allows a more isothermal compression of the gas to a high density and $\rho $R at the center of the target. The radiative cooling caused by mixing of high Z material into the gas region was considered to degrade to the performance of ICF capsule. However, a trace of high-Z doping enhances both the TN performance as well as the hot-spot $\rho $R. Overall, for a transparent pusher design, over 38{\%} of improvement of gas (hot-spot) $\rho $R and over 200{\%} increase of the yield rate compared to the baseline design have been achieved using this. For an opaque pusher design, no TN performance improvement had been observed in calculation. [Preview Abstract] |
Tuesday, November 12, 2013 4:12PM - 4:24PM |
JO7.00012: Suprathermal Ion Populations in ICF Plasmas -- Implications for Diagnostics and Ignition Patrick Knapp, Paul Schmit, Daniel Sinars We report on investigations into the effects of suprathermal ion populations on neutron production in Inertial Confinement and Magneto-Inertial Fusion plasmas. In a recent article we showed that a suprathermal population taking the form of a power-law in energy will significantly modify the shape and width of the neutron spectrum and can dramatically increase the fusion reactivity compared to the Maxwellian case [1]. Specific diagnostic signatures are discussed in detail. We build on this work to include the effect of an applied magnetic field on the neutron spectra, isotropy and production rate. Finally, the impact that these modifications have on the ability to reach high fusion yields and ignition is discussed. \\[4pt] [1] P.F. Knapp, D.B. Sinars and K.D. Hahn, Phys. Plasmas 20, 062701 (2013) [Preview Abstract] |
Tuesday, November 12, 2013 4:24PM - 4:36PM |
JO7.00013: ICF Experiments with the first two bundle beams of Shengguang III laser facility Yongkun Ding, Shaoen Jiang, Shenye Liu, Sanwei Li, Tianxuan Huang, Shiyang Zhou, Wenhua Ye, Wenbin Pei, Shaoping Zhu, Baohan Zhang, Xiaodong Chen, Weiyan Zhang Shengguang(SG) III laser facility is under construction. It was designed as a $\sim$ 100kJ laser fusion driver with 48 beams in 6 bundles. The output of SGIII is about 180kJ in 3ns, or over 60kJ in 1ns with 0.351$\mu $m laser. The beams are arranged in four incident angles similar to NIF and LMJ. Pulse shaping, beams smoothing, and center wavelength adjusting are equipping on SGIII, so it will be a key experimental platform for the goal of ignition for China. Construction of SGIII will be completed in the middle of 2014, and the first two bundles have been integrated to test its performance. We designed a series of experiments to investigate physics about hohlraum and indirectly driven implosion. Good results have been obtained ,that implied the performance of SGIII is close to the design. [Preview Abstract] |
Tuesday, November 12, 2013 4:36PM - 4:48PM |
JO7.00014: A new ignition scheme using hybrid indirect-direct drive for ICF Zhengfeng Fan, Mo Chen, Zhensheng Dai, Hong-bo Cai, Shao-ping Zhu, W.Y. Zhang, X.T. He A new hybrid indirect-direct-drive ignition scheme is proposed: the fuel capsule encased in a hohlraum is compressed first by indirect-drive x rays, and then accelerated and ignited by both direct-drive lasers and x rays. In this scheme, between the radiation and electron ablation fronts separately formed by indirect-drive x rays and direct-drive lasers there can appear a high-density plateau that suppresses the rarefaction wave at the radiation ablation front ahead of the imploding capsule. It is shown by numerical simulations that the drive pressure is significantly enhanced and multiple shock reflections off the main fuel/hot spot interface during the deceleration phase of the compression are prevented, leading to rapid compression and heating of the fuel to reach hot-spot ignition condition there before stagnation. Practically, the hybrid drive can implode the capsule to a high velocity (430 km/s) at a low convergence ratio (25), and the hydrodynamic instability and drive asymmetry are significant suppressed, especially, at the main fuel/hot spot interface the hydrodynamic instability is decreased by several times as compared with the conventional indirect drive. [Preview Abstract] |
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