Bulletin of the American Physical Society
50th Annual Meeting of the Division of Plasma Physics
Volume 53, Number 14
Monday–Friday, November 17–21, 2008; Dallas, Texas
Session TO5: Compression and Burn II |
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Chair: Thomas Boehly, University of Rochester Room: Reunion C |
Thursday, November 20, 2008 9:30AM - 9:42AM |
TO5.00001: Magnetized Hot-Spot Implosions Via Laser-Driven Flux Compression O.V. Gotchev, R. Betti, P. Chang, J.P. Knauer, D.D. Meyerhofer, J.A. Frenje, C.K. Li, M. Manuel, R.D. Petrasso, F.H. S\'eguin Cylindrical, DD-filled targets were seeded with $\sim $0.1-MG magnetic fields from low-mass coils, energized by a compact capacitive discharge system. They were then imploded on the OMEGA laser to compress the embedded magnetic field to high values. The compression of the internal magnetic flux was measured with a proton deflectrometry technique\footnote{ J.R. Rygg \textit{et al}., Science \textbf{319}, 1223 (2008).} optimized for this application. Strong magnetic fields localized in the hot spot were observed. Comparison with Monte Carlo simulations of the proton transport through the target area revealed fields, compressed to many tens of megagauss. Application of the resulting hot-spot thermal insulation to implosions with enhanced gain (or lower ignition-energy requirements than what is possible in conventional ICF) is discussed. The strong magnetic fields generated in this manner can also be used in a variety of non-fusion experiments such as laboratory astrophysics, material science, etc. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement Nos. DE-FC52-08NA28302 and DE-FG02-04ER54768. [Preview Abstract] |
Thursday, November 20, 2008 9:42AM - 9:54AM |
TO5.00002: Transport of Energetic Electrons Produced from Two-Plasmon Decay in the 1-D Hydrodynamic Code \textit{LILAC} J.A. Delettrez, V.N. Gocharov, P.B. Radha, C. Stoeckl, A.V. Maximov, T.C. Sangster, J.A. Frenje, D. Shvarts The effect of two-plasmon-decay electrons on direct-drive cryogenic implosions on the OMEGA laser is modeled. The electrons are created at the quarter-critical surface when a threshold depending on laser intensity and local thermal-electron conditions is attained. The fraction of the absorbed laser energy is a parameter that depends exponentially on the threshold condition and saturates at laser intensities of 10$^{15}$ W/cm$^{2}$. The source distribution is a Maxwellian with a temperature scaling inferred from hard x-ray measurements. The electrons are transported with a multi-group diffusion model for the low energy electrons and a straight-line model for the high-energy electrons. Simulation results from warm plastic and cryogenic implosions are compared with the following diagnostics: the hard x-ray emission, the fast-ion spectrum, and the neutron-averaged areal density at stagnation. 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] |
Thursday, November 20, 2008 9:54AM - 10:06AM |
TO5.00003: Nonlocal Ion-Heat Transport and Viscosity in ICF Implosions S. Skupsky, V.N. Goncharov, D. Li During shock propagation and coalescence in the vapor region of ICF targets, the ion mean free path can become large compared to relevant spatial scale lengths and to the size of computational cells in numerical simulations. During this time, a classical treatment of hydrodynamics may not be valid. To investigate the effect of these long mean-free-path ions on the simulation of ICF implosions, we have developed models to treat nonlocal ion transport, and we have applied them to the simulation of experiments on the OMEGA laser and ignition designs for the NIF. This presentation will focus on a time-dependent, quasi-Monte-Carlo approach in which ions are tracked through the plasma, and energy, momentum, and mass are deposited nonlocally. 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] |
Thursday, November 20, 2008 10:06AM - 10:18AM |
TO5.00004: Modeling of Multiple-Ion Heat Transport in ICF Implosion D. Li, V.N. Goncharov, A.V. Maximov, S. Skupsky, I.V. Igumenshchev Both the fuel and ablator material in target designs for direct- and indirect-drive ICF implosions consist of a mixture of different elements (D and T, H and C, etc.). In calculating the thermal conduction in both hot plasma corona and in the compressed fuel core, the hydrodynamic codes typically approximate the multi-ion plasma with an average single-ion model. Such an approximation, as pointed out earlier,\footnote{E.M. Epperlein, R.W. Short, and A. Simon, Phys. Rev. E \textbf{49}, 2480 (1994).} could give large errors in calculating ion thermal flux and the electron-ion energy exchange rate, especially when the mass or charge ratio between different species is large. To assess the accuracy of the average-ion model in modeling ICF-related experiments, a full multi-species transport model was implemented in the 1-D hydrocode \textit{LILAC}. This talk will present results of simulations with the new ion-thermal conduction model applied to room temperature, as well as cryogenic, implosions on OMEGA. 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] |
Thursday, November 20, 2008 10:18AM - 10:30AM |
TO5.00005: Optimization of Multiple-Picket, Direct-Drive, Laser Pulse Shapes with Foam Shells J.P. Knauer, V.N. Goncharov, J.A. Delettrez, V.Yu. Glebov, F.J. Marshall, J.A. Frenje, C.K. Li, R.D. Petrasso, F.H. S\'eguin The performance of high-gain, direct-drive inertial confinement fusion (ICF) targets is maximized by optimizing the timing of two to four converging shock waves. Targets with improperly timed shock waves have high entropies and take more energy to compress to ignition conditions. The timing of these shock waves, calculated by hydrodynamic simulations, has been checked experimentally for planar targets and needs to be verified experimentally for converging shocks. Warm, foam shell targets are being investigated as hydrodynamic equivalents to cryogenic D$_{2}$ and DT targets to optimize the convergent shock-wave timing. Foam shell targets have been used on experiments at the OMEGA Laser Facility to optimize multiple-picket laser pulse shapes. The results from this study will be presented along with a comparison of hydrodynamic simulation results to the experimental measurements. 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] |
Thursday, November 20, 2008 10:30AM - 10:42AM |
TO5.00006: Multiple-Picket, Direct-Drive Target Designs for OMEGA and the NIF V.N. Goncharov, T.C. Sangster, T.R. Boehly, P.B. Radha, R.L. McCrory, D.D. Meyerhofer, S. Skupsky Multiple-picket, direct-drive target designs are considered for the National Ignition Facility. They have several advantages over conventional designs with continuous drive pulses. Because of inaccuracies in modeling EOS and laser coupling, the slope of the intensity rise in a continuous-pulse design must be experimentally ``tuned'' to prevent steepening of the compression wave front into a shock. Recent shock-velocity measurements\footnote{T.R. Boehly \textit{et al}., ``Timing of Multiple Shock Waves in Cryogenic-Deuterium Targets,'' invited talk, this conference.} indicate that the shock tuning can be facilitated by replacing this rise region with two or three pickets. The required shock-timing accuracy can be achieved in this case by adjusting energies of individual pickets. In addition, the multiple-picket design produces an enhanced adiabat steepening at the ablation front that increases target robustness to the hydro instability. 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] |
Thursday, November 20, 2008 10:42AM - 10:54AM |
TO5.00007: Numerical Investigation of OMEGA Saturn Implosions A. Shvydky, J.A. Marozas, R.S. Craxton, I.V. Igumenshchev, F.J. Marshall, P.W. McKenty, T.C. Sangster, S. Skupsky, R.L. McCrory The basic concept behind the Saturn polar-drive scheme\footnote{ R.S. Craxton and D.W. Jacobs-Perkins, Phys. Rev. Lett. \textbf{94}, 095002 (2005).} is the use of a CH equatorial ring which, by refracting the intentionally skewed x-ray-drive laser beams toward the target equator, minimizes the overall illumination nonuniformities during the implosion. In this paper Saturn target implosions on OMEGA are investigated numerically using the 2-D radiation hydrodynamic code \textit{DRACO} with 3-D ray trace. Results indicate the development of large, localized nonuniformities in the shell near the target equator. Simulation results demonstrate that these perturbations are caused by undesirable focusing of laser rays refracted by the ring. The results will be compared with OMEGA experiments examining several ring sizes and positions aimed at reducing the illumination nonuniformities and improving target performance. 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] |
Thursday, November 20, 2008 10:54AM - 11:06AM |
TO5.00008: 1.0-MJ CH-Foam Ignition Targets on the NIF Using 1-D Multi-FM SSD with 0.5 THz of Bandwidth J.A. Marozas, J.D. Zuegel, T.J.B. Collins The 1-D multiple-frequency-modulator (Multi-FM) smoothing by spectral dispersion (SSD) system smoothes low $\ell $-mode ($\ell <$ 100) illumination nonuniformities by taking advantage of multiple color cycles dispersed across the laser beam cross section. Multi-FM systems do not produce unsmoothed resonant features in the higher $\ell $ modes as found in single-modulator systems. The 1-D Multi-FM SSD system is being investigated to provide adequate smoothing with a bandwidth of only 0.5 THz so that dual-frequency-conversion crystals are not required. Cryogenic, 1.0-MJ CH-foam ignition designs are being studied using 1-D Multi-FM SSD and the performance will be compared to the full 2-D SSD, 1.0-THz system using the 2-D radiation-hydrodynamics code \textit{DRACO}. Such \textit{DRACO} simulations incorporate the coherence-time model supported by far-field simulations. 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] |
Thursday, November 20, 2008 11:06AM - 11:18AM |
TO5.00009: Initial 3-D HYDRA Simulations of OMEGA Cryogenic Implosions P.W. McKenty, K.S. Anderson, V.N. Goncharov, D.H. Edgell, D.D. Meyerhofer, T.C. Sangster, R.L. McCrory, M.M. Marinak The Laboratory for Laser Energetics continues to examine the performance of cryogenically fueled D$_{2}$ and DT direct-drive capsule implosions. Of particular concern is the interplay between the initial uniformity of the ice layer which is usually directed into a north--south attitude and the target offset nonuniformity, that is mainly an east--west perturbation. Such combinations are inherently three-dimensional in nature and have not previously been accurately examined. This paper will first present a comparison of the results from both 2-D and 3-D simulations of target offset. Additional 3-D results will then be presented examining the combined effect of target offset and ice-layer smoothness on target performance. These 3-D results will be compared with 2-D simulations to examine the differences made when approximations to 3-D perturbations are applied to the 2-D simulations. 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] |
Thursday, November 20, 2008 11:18AM - 11:30AM |
TO5.00010: Simulations of Polar-Drive NIF Targets Optimized for High Neutron Yields R.S. Craxton, P.W. McKenty, J.A. Marozas, A.M. Cok Thin-shell, DT-filled, room-temperature targets driven directly on the NIF using polar drive\footnote{ A.M. Cok, R.S. Craxton, and P.W. McKenty, ``Polar-Drive Designs for Optimizing Neutron Yields on the National Ignition Facility,'' submitted to Phys. Plasmas.} promise high fusion yields for neutron diagnostic development. These targets have been modeled with three codes: \textit{LILAC}, to optimize the 1-D design; \textit{SAGE}, to optimize the pointing uniformity; and \textit{DRACO}, to predict the yield from 2-D implosion simulations. The predicted yields (in the range of 10$^{15}$ to 10$^{16}$ neutrons for laser energies from 350 kJ to 1 MJ) are consistent with earlier data on OMEGA (10$^{14}$ neutrons at 30 kJ). 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] |
Thursday, November 20, 2008 11:30AM - 11:42AM |
TO5.00011: Shock Ignition: A New Approach to High Gain Targets for the National Ignition Facility L. John Perkins, Kai Lafortune, Laurent Divol, Riccardo Betti Shock-ignition is being studied as a future option for achieving high target gains on NIF, offering the potential for testing high yield (200MJ), reactor-relevant targets for inertial fusion energy and targets with appreciable gains at drive energies much less than 1MJ. In contrast to conventional hotspot ignition, the assembly and ignition phases are separated by imploding a high mass shell at low velocity. The assembled fuel is then separately ignited by a strong, spherical shock driven by a high intensity spike at the end of the pulse and timed to reach the center as the main fuel is stagnating. Because the implosion velocity is significantly less than that required for hotspot ignition, considerably more fuel mass can be assembled and burned for the same kinetic energy in the shell. Like fast ignition, shock ignition could achieve high gains at low drive energy, but has the advantages of requiring only a single laser with less demanding timing and spatial focusing requirements. We will discuss gain curves for shock-ignited NIF targets in both UV and green light and examine the feasibility of designs that employ indirect drive fuel assembly with direct drive shock ignition [Preview Abstract] |
Thursday, November 20, 2008 11:42AM - 11:54AM |
TO5.00012: Shock-ignited, sub-MJ, green-light, direct-drive, ICF targets potentially fieldable on the NIF Kai N. LaFortune, L. John Perkins, Laurent Divol Shock ignition holds the potential for greatly increasing fusion yields and facilitating robust, direct-drive, sub-MJ targets[1]. NIF's current polar-weighted drive geometry, although optimized for indirect drive, can potentially be used for polar, direct-drive experiments. Because shock-ignition decouples the compression and ignition phases of target assembly, targets have reduced sensitivity to hot-electrons, and thus using the NIF at the second-harmonic wavelength of 526 nm may potentially be advantageous. Rad-hydro-burn simulations using HYDRA of shock-ignited, direct-drive targets using NIF's drive geometry, requiring less than 1 MJ of second-harmonic drive energy to achieve gains of up to 100 are studied. 1-D scoping studies have been performed to outline the source and target requirements. The robustness of the targets is explored with 2-D stability studies and examination of laser plasma instabilities. [1] R.Betti, C.Zhou, L.J.Perkins, K.Andrson, ``Shock Ignition of Thermonuclear Fuel with High Areal Density'', Phys Rev. Lett~ 98, No. 15 (2007) [Preview Abstract] |
Thursday, November 20, 2008 11:54AM - 12:06PM |
TO5.00013: Direct drive target designs for laser fusion energy Andrew J. Schmitt, J.W. Bates, D.E. Fyfe, S.P. Obenschain, S.T. Zalesak, M. Quigley, R. Betti We discuss the development of high-gain directly-driven targets for energy applications. We have simulated, in 1D and 2D, implosions of both conventional and shock-ignition targets in the low energy regime ($<$1MJ). All designs take advantage of efficient energy coupling and higher pressures available with 0.248$\mu m$ wavelength KrF light and zooming of the focal spot. We find significantly higher yields with shock ignition: gains near 100x at 0.3 MJ and over 200x at 1 MJ. Both conventional and shock ignited targets are fairly robust to achievable outer and inner surface finishes and inner ice surfaces. Rayleigh-Taylor (RT) instabilities are controlled with adiabat tailoring and low-aspect ratio targets. We assess risks and sensitivities due to hydro instabilities, laser-plasma instabilities, beam pointing and power balance, and the higher convergence ratios of these smaller targets. [Preview Abstract] |
Thursday, November 20, 2008 12:06PM - 12:18PM |
TO5.00014: Target designs for inertial confinement fusion using approximately 1 MJ of direct KrF laser light Jason Bates, Andrew Schmitt, David Fyfe, Steve Obenschain, Steve Zalesak We report on recent numerical simulations with the FAST radiation hydro-code of direct-drive target implosions. Our discussion focuses on both conventional and ``shock-ignited''\footnote{R. Betti, C.D. Zhou, K.S. Anderson, {\it et al.}, Phys.~Rev.~Lett.~{\bf 98}, 155001 (2007).} target designs that utilize about 1 MJ of KrF laser light. Each class of designs has its own advantages, but it appears that shock-ignited targets may be superior in that gains of approximately 200 can be achieved with only 862 kJ of laser energy, according to one-dimensional simulations. This represents a significant improvement over the conventional ``central-hot-spot'' approach to laser fusion energy. In this presentation, we examine the two-dimensional stability of both types of targets by analyzing their performance in the presence of realistic inner- and outer-surface perturbations. Other important design issues, such as the susceptibility of the targets to laser-plasma instabilities and beam power misalignment, are also briefly addressed. [Preview Abstract] |
Thursday, November 20, 2008 12:18PM - 12:30PM |
TO5.00015: Robust target implosion in heavy ion fusion Shigeo Kawata, Yoshifumi Iizuka, Tomohiro Kodera, Alexandar Ogoyski In heavy ion inertial fusion (HIF) a robust mode of target implosion is proposed to mitigate the beam illumination non-uniformity and the Rayleigh-Taylor (R-T) instability growth. In the HIF target implosion, key issues include uniformity of heavy ion beam (HIB) illumination, target implosion symmetry, compressed fuel ignition, reduction of the R-T instability growth, etc [1]. In the robust target in HIF, an oscillating implosion acceleration is employed to reduce the R-T instability growth, and a low-density foam layer is also inserted to enhance the radiation conversion efficiency from. The oscillating acceleration can be introduced by HIB axis oscillation, which can be easily realized in an actual accelerator final element. The oscillating acceleration introduces a new method of the R-T instability growth control. In the robust foam target, the radiation converted is confined and reduces the HIB illumination non-uniformity, though the HIBs illumination scheme is spherically symmetric and the target is also spherically symmetric. Therefore, the foam target irradiated by the oscillating HIBs can serve a robust direct-indirect hybrid mode of the symmetric target implosion in HIF. [1] Phys. of Plasmas, 12 (2005) 122702; NIMA, 577 (2007) 21. [Preview Abstract] |
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