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 BO5: Hohlraums I |
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Chair: Robin Benedetti, Lawrence Livermore National Laboratory Room: 230 B |
Monday, October 31, 2016 9:30AM - 9:42AM |
BO5.00001: Improving Hohlraums for High Foot Implosions D. E. Hinkel, L. F. Berzak Hopkins, T. Ma, J. E. Ralph, F. Albert, L. R. Benedetti, P. M. Celliers, T. Doeppner, C. S. Goyon, N. Izumi, L. C. Jarrott, S. F. Khan, J. L. Kline, A. L. Kritcher, G. A. Kyrala, S. R. Nagel, A. E. Pak, P. Patel, M. D. Rosen, J. R. Rygg, M. B. Schneider, D. P. Turnbull, C. B. Yeamans, D. A. Callahan, O. A. Hurricane Analysis of High Foot implosions show that performance has been limited by the radiation drive environment, i.e., the hohlraum. Demonstrated here is that improvements in the radiation environment result in an enhancement in implosion performance. This is accomplished by using a longer, larger case-to-capsule ratio hohlraum at lower gas fill density. At fixed laser energy, High Foot implosions driven with this hohlraum have achieved a 1.4 x increase in stagnation pressure, with an accompanying relative increase in fusion yield of 50{\%}. Low mode asymmetries are still present, however, and are most likely a consequence of poor inner beam propagation through the hohlraum to the wall. Presented here are results from these High Foot implosions, as well as analyses of inner beam propagation, and additional hohlraum improvements that further ameliorate the implosion. [Preview Abstract] |
Monday, October 31, 2016 9:42AM - 9:54AM |
BO5.00002: Measurements of Hard X-Ray Emission Suggest Absorption Along the Path of the Inner Beams in High Foot Implosion Experiments on the NIF Joseph Ralph, Arthur Pak, Landen Otto, Andrea Kritcher, Tammy Ma, Jarrott Charles, Debra Callahan, Denise Hinkel, Laura Berzak Hopkins, John Moody, Shahab Khan, Tilo Doeppner, Ryan Rygg, Omar Hurricane The current high foot hohlraum design fielded on the National Ignition Facility is aimed at providing uniform x-ray drive to provide a spherical implosion by lowering the gas fill from 1.6 to 0.6 mg/cc and increasing the hohlraum width from 5.75 to 6.72 mm while maintaining the same 1.8 mm capsule diameter from previous designs. These changes are intended to improve beam propagation without the need for crossed beam energy transfer. Analysis of the measurements of hard x-ray emission from the gated x-ray detector (GXD) and the static x-ray imager (SXI) looking through the laser entrance hole indicate a significant fraction of the inner beam incident energy is absorbed in the high z blow-off region (either uranium or gold) before reaching the inner wall near the equator. Comparison of inner beam absorption in this region and its effect on the implosion symmetry measurements will be presented. Additionally, the sensitivity of this absorption feature and therefore the implosion symmetry to the pulse shape, hohlraum fill pressure and fraction of energy in beams depositing energy at the hohlraum equator will be discussed. 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] |
Monday, October 31, 2016 9:54AM - 10:06AM |
BO5.00003: Metrics for comparing drive on the capsule for indirect drive implosions on NIF Debra Callahan, Omar Hurricane, John Moody, Laura Berzak Hopkins, Laurent Divol, Tilo Doeppner, Eduard Dewald, Denise Hinkel, Shahab Khan, Andrea Kritcher, Sebastien LePape, Tammy Ma, Nathan Meezan, Joseph Ralph, Steven Ross Radiation drive on the capsule is an important parameter in ICF because it determines the implosion velocity. For indirect drive, the effective capsule drive is a combination of hohlraum and capsule physics. The hohlraum converts the laser energy into xrays – both flux and spectrum. The xray drive is a function of the hohlraum size, material, and hohlraum fill in addition to being a function of the laser power and energy. The timing of the drive with respect to the capsule implosion trajectory plays a role in the way in the way the capsule absorbs the energy [1] as does the choice of ablator material and capsule dopant. In this presentation, we will look at trends in the data from both hohlraum (Dante, SXI) and capsule diagnostics (bangtime, capsule xray yield) as a method for comparing the drive on the capsule for a variety of designs. [1] O. A. Hurricane, et al, this meeting [Preview Abstract] |
Monday, October 31, 2016 10:06AM - 10:18AM |
BO5.00004: Laser propagation in simulations of low fill density hohlraums Nathan Meezan, L. F. Berzak Hopkins, N. Izumi, L. Divol, D. E. Hinkel, J. E. Ralph, J. D. Moody, D. A. Callahan We present analysis of laser propagation in simulations of low fill density hohlraums on the National Ignition Facility (NIF). Simulations using the radiation hydrodynamic code \textsc{hydra} are compared in 2D and 3D. The absorption of laser rays in different materials and spatial locations is extracted from the simulations to identify where and when the inner cone laser beams undergo significant absorption. Inner cone laser beams can be absorbed in the outer cone ``gold bubble'' or in the region where the ablator and hohlraum material interact. The simulations provide guidance on which hohlraum mitigation methods will be most effective at improving inner beam propagation. [Preview Abstract] |
Monday, October 31, 2016 10:18AM - 10:30AM |
BO5.00005: Design options for improved performance with high-density carbon ablators and low-gas fill hohlraum targets L. Berzak Hopkins, L. Divol, S. LePape, N. B. Meezan, E. Dewald, D. Ho, S. Khan, A. Pak, J. Ralph, J. S. Ross Recent simulation-based and experimental work using high-density carbon ablators in unlined uranium hohlraums with 0.3 mg/cc helium fill have demonstrated round implosions with minimal evolution of Legendre moment P2 during burn. To extend this promising work, design studies have been performed to explore potential performance improvements with larger capsules, while maintaining similar case-to-capsule target ratios. We present here the results of these design studies, which will motivate a series of upcoming experiments at the National Ignition Facility. [Preview Abstract] |
Monday, October 31, 2016 10:30AM - 10:42AM |
BO5.00006: Comparison of high-density carbon implosions in unlined uranium versus gold hohlraums Eduard Dewald, Nathan Meezan, Riccardo Tommasini, Shahab Khan, Andrew MacKinnon, Laura Berzak Hopkins, Laurent Divol, Sebastien LePape, Alastair Moore, Marilyn Schneider, Arthur Pak, Abbas Nikroo, Otto Landen In Inertial Confinement Fusion (ICF) implosions, laser energy is converted to x-ray radiation in hohlraums with High-Z walls. At radiation temperatures near 300 eV relevant for ICF experiments, the radiative losses in heating the wall are lower for~U than for Au hohlraums [1]. Furthermore, the intensity of the ``M-band'' x-rays with photon energies h$\nu $ \textgreater 1.8 keV is lower for uranium, allowing for reduced capsule dopant concentrations employed to minimize inner ablator preheat and hence keep favorable fuel/ablator interface Atwood numbers. This in turn improves the ablator rocket efficiency and reduces the risk of polluting the hot-spot with emissive dopant material. The first uranium vacuum hohlraum experiments on the National Ignition Facility (NIF) with undoped high-density carbon (HDC, or diamond) capsules have demonstrated 30 {\%} lower ``M-band'' intensity relative to Au, resulting in lower inflight ablator thickness due to reduced preheat. In addition, fusion neutron yields are 2x higher in U than in Au hohlraums for D$_{\mathrm{2}}$-gas filled capsule implosions at ICF relevant velocities of 380 $+$/-~20 km/s. These results have led the NIF ICF implosions to routinely employ U hohlraums. [1] J. Schein, O.S. Jones, M. Rosen, E. Dewald, S. Glenzer, et al, \textit{Phys. Rev. Lett. }\textbf{98}, 175003 (2007). Prepared by LLNL under Contract DE-AC52-07NA27344. [Preview Abstract] |
Monday, October 31, 2016 10:42AM - 10:54AM |
BO5.00007: Direct-drive Energetics of laser-Heated Foam Liners for Hohlraums Alastair Moore, Cliff Thomas, Kevin Baker, John Morton, Ted Baumann, Monika Biener, Suhas Bhandarkar, Denise Hinkel, Oggie Jones, Nathan Meezan, John Moody, Abbas Nikroo, Mordy Rosen, Warren Hsing Lining the walls of a high-Z hohlraum cavity with a low-density foam is predicted to mitigate the challenge presented by hohlraum wall expansion. Once heated, wall material quickly fills the cavity and can impede laser beam propagation. To avoid this, ignition hohlraums are typically filled with a gas or irradiated with a short ($<$ 10 ns) laser pulse. A gas-fill has the disadvantage that it can cause laser plasma instabilities (LPI), while a short laser pulse limits the design space to reach low-adiabat implosions. Foam-liners offer a potential route to reduce wall motion in a low gas-fill hohlraum with little LPI. Results from quasi 1-D experiments performed at the NIF are presented These characterize the x-ray conversion efficiency, backscattered laser energy and heat propagation in a 250$\mu$m thick Ta$_2$O$_5$ or ZnO foam-liners spanning a range of densities from underdense to overdense, when irradiated at up to 4.9 x 10$^{14}$ W/cm$^2$ is incident on a planar foam sample, backed by a Au foil and generates a radiation temperature of up to 240eV - conditions equivalent to a single outer cone beam-spot in an ignition hohlraum. [Preview Abstract] |
Monday, October 31, 2016 10:54AM - 11:06AM |
BO5.00008: Use of hohlraum liners to improve hohlraum performance Suhas Bhandarkar, Kevin Baker, Cliff Thomas, Alastair Moore, Don Bennett, Ted Baumann, Dick berger, Monika Biener, Debbie callahan, Daniel Casey, Peter Celliers, Fred Elsner, Sean Felker, Denise Hinkel, Warren Hsing, Haibo Huang, Oggie Jones, Nino Landen, Jose Milovich, Abbas Nikroo, Rick olson, Brian Spears, Michael Stadermann, David Strozzi, John Moody Hohlraum liners can be used to improve many aspects in hohlraum physics. They can be used to modify the x-ray spectrum, thereby reducing the symmetry swings induced by m-band driven primarily from the outer beam spots. Simulations indicate that reducing the level of x rays between 1.8 to 4 keV can allow the reduction or elimination of dopant in ICF capsules, thereby reducing the ablation front growth factors and leading to a more stable implosion. Liners can be used to introduce low Z species into the wall to alter the gain of LPI. At the lowest densities they can be used to greatly reduce wall motion. Diminished wall motion would reduce symmetry swings and allow some ICF platforms to operate at lower gas fill densities, thereby reducing LPI and CBET. All of these are beneficial to the performance of the hohlraum. In this presentation experimental results from liner experiments conducted on the NIF will be presented. Prepared by LLNL under Contract DE-AC52-07NA27344 [Preview Abstract] |
Monday, October 31, 2016 11:06AM - 11:18AM |
BO5.00009: X-ray Measurements of Laser Irradiated Foam Filled Liners Siddharth Patankar, Derek Mariscal, Clement Goyon, Kevin Baker, Stephan Maclaren, Jim Hammer, Ted Baumann, Peter Amendt, Joseph Menapace, Bob Berger, Bedros Afeyan, Max Tabak, Sham Dixit, Sung Ho Kim, John Moody, Ogden Jones Low-density foam liners are being investigated as sources of efficient x-rays. Understanding the laser-foam interaction is key to modeling and optimizing foam composition and density for x-ray production with reduced backscatter. We report on the experimental results of laser--irradiated foam liners filled with SiO$_{\mathrm{2}}$ and Ta$_{\mathrm{2}}$O$_{\mathrm{5}}$ foams at densities between 2 to 30mg/cc. The foam liners consist of polyimide tubes filled with low-density foams and sealed with a gold foil at one end. The open end of the tube is driven with 250J of 527nm laser light in a 2ns 2-step pulse using the Jupiter Laser Facility at LLNL. A full aperture backscatter system is used to diagnose the coupled energy and losses. A streaked x-ray camera and filtered x-ray pinhole cameras are used to measure laser penetration into the low-density foam for different mass densities. A HOPG crystal spectrometer is used to estimate a thermal electron temperature. Comparisons with beam propagation and x-ray emission simulations are presented. [Preview Abstract] |
Monday, October 31, 2016 11:18AM - 11:30AM |
BO5.00010: Plasma interpenetration study on the Omega laser facility Sebastien Le Pape, Laurent Divol, Steven Ross, Scott Wilks, Peter Amendt, Laura Berzak Hopkins, Gael Huser, John Moody, Andy Mackinnon, Nathan Meezan The Near Vacuum Campaign on the National Ignition Facility has sparked an interest on the nature of the gold/carbon interface at high velocity, high electron temperature, low-electron density. Indeed radiation-hydrodynamic simulations have been unable to accurately reproduce the experimental shape of the hot spot resulting from implosion driven in Near Vacuum Holhraum. The experimental data are suggesting that the inner beams are freely propagating to the waist of the hohlraum when simulations predict that a density ridge at the gold/carbon interface blocks the inner beams. The discrepancy between experimental data and simulation might be explained by the fluid description of the plasma interface in a rad-hydro code which is probably not valid in when two plasma at high velocity, high temperature are meeting. To test our assumption, we went to the Omega laser facility to study gold/carbon interface in the relevant regime. Time resolved images of the self-emission as well as Thomson scattering data will be presented. For the first time, a transition from a multifluid to a single fluid is observed as plasmas are interacting. 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] |
Monday, October 31, 2016 11:30AM - 11:42AM |
BO5.00011: ABSTRACT WITHDRAWN |
Monday, October 31, 2016 11:42AM - 11:54AM |
BO5.00012: A novel three-axis cylindrical hohlraum designed for inertial confinement fusion ignition Shaoen Jiang, Longyu Kuang, Hang Li, Longfei Jing, Zhiwei Lin, Lu Zhang, Lilin Li, Yongkun Ding, Jian Zheng, Jie Liu A novel ignition hohlraum for indirect-drive inertial confinement fusion is proposed, which is named as three-axis cylindrical hohlraum (TACH). TACH is a kind of 6 laser entrance holes (LEHs) hohlraum, which is made of three cylindrical hohlraums orthogonally jointed. Laser beams are injected through every entrance hole with the same incident angle of 55°. The view-factor simulation result shows that the time-varying drive asymmetry of TACH is no more than 1.0{\%} in the whole drive pulse period without any supplementary technology such as beam phasing etc. Its coupling efficiency of TACH is close to that of 6 LEHs spherical hohlraum with corresponding size. Its plasma-filling time is close to typical cylindrical ignition hohlraum. Its laser plasma interaction has as low backscattering as the outer cone of the cylindrical ignition hohlraum. Therefore, the proposed hohlraum provides a competitive candidate for ignition hohlraum. [Preview Abstract] |
Monday, October 31, 2016 11:54AM - 12:06PM |
BO5.00013: A Novel Spherical Hohlraum Design with Tetrahedral 4 Laser Entrance Holes and High Radiation Performance Yunbao Huang, Longfei Jing, Shaoen Jiang As usual cylindrical hohlraum with double laser ring cones may lead to serious CBET, and LPI effect, spherical hohlraum with octahedral 6 LEHs and single laser ring cone is investigated and presented to achieve higher radiation symmetry during the fusion process. However, it has several potential problems such as the long run distance and the close distance between the spot and their closet LEH for the laser beams, smaller space is left for diagnose, and the assembly of centrally located capsule. In this paper, based on view-factor transportation model, we investigate the radiation symmetry and the drive temperature on the centrally located capsule in the spherical hohlraum with tetrahedral 4 LEHs and single laser ring cone, since there is more available space for laser disposition and diagnose. Then, such target is optimized on the laser beam pointing direction and shape sizes to achieve high radiation performance, or the radiation symmetry and drive temperature on the capsule.Finally, a novel spherical hohlraum with optimal laser beam pointing and shape size has been demonstrated to have almost similar radiation symmetry (the radiation asymmetry variation is no more than 0.2{\%}), and higher drive temperature (the temperature has been increased by 1.73{\%}, and additional 133 KJ energy of 2MJ energy for fusion can be utilized). [Preview Abstract] |
(Author Not Attending)
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BO5.00014: A Novel Spherical Hohlraum Design with Tetrahedral 4 Laser Entrance Holes and High Radiation Performance. Longfei Jing, Yunbao Huang, Shaoen Jiang, Haiyan Li, Tianxuan Huang, Yongkun Ding As usual cylindrical hohlraum with double laser ring cones may lead to serious CBET effect, spherical hohlraum with octahedral 6 LEHs and single laser ring cone is presented to achieve higher radiation symmetry during the fusion process. However, it has several potential problems such as the long run distance, smaller space is left for diagnose, and the assembly of centrally located capsule. In this paper, we investigate the radiation performance, i.e., radiation symmetry and drive temperature on the capsule in the spherical hohlraum with tetrahedral 4 LEHs and single laser ring cone, since there is more available space for laser disposition and diagnose. Then, such target is optimized on the laser beam pointing direction and shape sizes to achieve high radiation performance, or the radiation symmetry and drive temperature on the capsule. Finally, a novel spherical hohlraum with optimal laser beam pointing and shape size has been demonstrated to have almost similar radiation symmetry (the radiation asymmetry variation is no more than 0.2{\%}), and higher drive temperature (the temperature has been increased by 1.73{\%}, and additional 133 KJ energy of 2MJ energy for fusion can be utilized).. [Preview Abstract] |
Monday, October 31, 2016 12:18PM - 12:30PM |
BO5.00015: Spherical hohlraum energetics study on the SGIII prototype laser facility Wenyi Huo, Zhichao Li, Yaohua Chen, Xufei Xie, Ke Lan We report on the first spherical hohlraum energetics experiment performed on the SGIII prototype laser facility. In the experiment, the radiation temperature of the spherical hohlraum is measured by using an array of flat-response x-ray detectors (FXRDs) through a LEH at different angles. The radiation temperature and M-band fraction inside the hohlraum are determined by the shock wave technique. The experimental results indicate that the radiation temperatures measured by the FXRDs depend on the observation angles and are related to the view field. For the first time, we obtained the angular distribution of the radiation temperature of spherical hohlraum. We find that the accurate hohlraum conversion efficiency can not be determined by using the measured radiation temperature of a FXRD at only one specific angle. As a result, what we obtained from the experimental measurements is a range of the hohlraum conversion efficiency, but not an accurate conversion efficiency. According to the experimental results, the conversion efficiency of the vacuum spherical hohlraum is in the range from 60{\%} to 80{\%}. This conversion efficiency is consistent with that of the cylindrical hohlraums used on the NOVA and the SGIII-prototype at the same energy scale. [Preview Abstract] |
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