Bulletin of the American Physical Society
51st Annual Meeting of the APS Division of Plasma Physics
Volume 54, Number 15
Monday–Friday, November 2–6, 2009; Atlanta, Georgia
Session TO5: ICF Simulations and Target Fabrications |
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Chair: Chuang Ren, University of Rochester Room: Hanover CDE |
Thursday, November 5, 2009 9:30AM - 9:42AM |
TO5.00001: NIF ignition target requirements, margins, and uncertainties: Status Nov. 2009 S.W. Haan, J.D. Salmonson, D.S. Clark, D.D. Ho, B.A. Hammel, D.A. Callahan, C.J. Cerjan, M.J. Edwards, S.P. Hathcett, O.L. Landen, J.D. Lindl, B.J. MacGowan, M.M. Marinak, D.H. Munro, H.F. Robey, B.K. Spears, L.J. Suter, R.P. Town, S.V. Weber, D.C. Wilson We describe simulations of NIF ignition targets, including Be, CH, and C-ablator designs. Requirements define all aspects of the experiment: fabrication, laser pulse, and features of pre-ignition experiments. We describe a model, normalized to simulations, that characterizes the margin of the target as a function of input parameters and uncertainties. The model is used to quantify the impact of each requirement, and to project the probability of ignition, both shot-to-shot variations and given systematic errors. This presentation emphasizes changes in the requirements and margin modeling in the last year, and the relative performance of the final CH, Be, and C designs. Recent work has concentrated on surface perturbations on the CH ablator, and composition variations in the Be shells. LLNL-ABS-414529. Prepared by LLNL under Contract DE-AC52-07NA27344. [Preview Abstract] |
Thursday, November 5, 2009 9:42AM - 9:54AM |
TO5.00002: High Gain High Efficiency Heavy-Ion Direct Drive Targets L.J. Perkins, J. Barnard, B.G. Logan, M. Hay New simulations of heavy ion (HI) direct drive fusion targets indicate that fusion gains of 50-80 may be achievable with less than 0.5MJ of heavy-ion drive energy. The inherently high efficiency of HI direct drive (15-20{\%} incident beam energy to shell kinetic energy) permit very simple all-DT targets with thick, low aspect ratio (A=2) shells that should exhibit high ablative R-T stabilization with robust in-flight stability characteristics. Beam symmetry studies show that 60 beams may suffice with rotated beam spots on the ablator. Present work is directed to obtaining target gain curves (i.e., target fusion energy gain versus HI drive energy), optimum HI pulse shapes in both ion kinetic energy and intensity, hydrodynamic stability, and the prospects of driving such targets with two-sided beam geometry as opposed to conventional 4-pi spherical symmetry that would permit simplified, more attractive target chamber geometries. Application to small heavy ion fusion test reactors with 10's MW average fusion powers, and to small fission fusion hybrids will be addressed. (Work performed by LLNL under Contract DE-AC52-07NA27344 on behalf of the Heavy Ion Fusion Virtual National Laboratory) [Preview Abstract] |
Thursday, November 5, 2009 9:54AM - 10:06AM |
TO5.00003: Simulations of the Shock-Timing Diagnostic Commissioning Experiments at the National Ignition Facility T.J.B. Collins, P.W. McKenty, K.S. Anderson, T.R. Boehly, M.A. Barrios, P.M. Celliers, D.G. Braun, M.M. Marinak As inertial confinement fusion targets are imploded, they generate several shock waves. The shock waves must be precisely timed to maintain a low target adiabat while achieving the necessary fuel compression. Shock timing of ignition experiments for the National Ignition Facility (NIF) will be confirmed using surrogate targets that allow one to determine shock speeds. The shock speeds are measured using an optical interferometer (VISAR) and a streaked optical pyrometer (SOP). This NIF platform will be tested with direct drive using impedance-matching experiments of a quartz sample and a stepped aluminum layer as a standard, based on previous experiments on OMEGA. These experiments have been simulated in three dimensions using the radiation hydrodynamics code \textit{HYDRA}. The results of these simulations will be presented and compared to initial experimental data. This work was supported by U. S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC52-08NA28302. [Preview Abstract] |
Thursday, November 5, 2009 10:06AM - 10:18AM |
TO5.00004: A Measurable Three-Dimensional Lawson Criterion and Hydro-Equivalent Curves For Inertial Confinement Fusion P. Chang, K. Anderson, R. Betti It is shown that a multi-dimensional ignition condition (Lawson criterion) can be cast in a form that depends on three measurable parameters of the compressed fuel assembly: the hot-spot ion temperature T, the neutron yield normalized to the 1-D prediction (Yield-Over-Clean, YOC) and the total areal density $\rho $R including the cold shell contribution. A family of marginal-ignition curves is derived in the $\rho $R-T plane. They are parameterized according to the YOC, and hydrodynamic simulations are compared with the ignition curves. On this plane, hydrodynamic equivalent curves show how a given implosion would perform with respect to the ignition condition when the laser-driver energy is varied. For 3 $<$ T $<$ 6 keV, the 3D ignition condition can be approximated by a simple formula : $\rho$R $\cdot$ T$^{2.6}$ $\cdot$ YOC $>$ 50g/cm$^{2}$ keV$^{2.6}$, where $\rho $R, T and YOC are the measured, neutron-averaged total areal density, hot-spot ion temperature and the neutron yield normalized to the 1-D prediction respectively. All quantities are calculated without accounting for the $\alpha $-particle energy deposition. Such a criterion can be used to measure the Margin in the THD (Tritium, Hydrogen, Deuterium-poor targets) campaign on the National Ignition Facility and to determine how surrogate D$_{2}$ ,THD, and sub-ignited DT target implosions perform with respect to the ignition threshold. [Preview Abstract] |
Thursday, November 5, 2009 10:18AM - 10:30AM |
TO5.00005: Enhancing the SRS model in pF3d to simulate off-resonant backscatter in NIC targets C.H. Still, E.A. Williams, D.E. Hinkel, A.B. Langdon, P.A. Michel Of particular interest to the National Ignition Campaign (NIC) is the amplification of laser backscatter, which is generated near the target wall, by crossing laser beams in the plasma region near the laser entrance hole (LEH)\footnote{P. A. Michel, private communication.} of an ignition target. We study here the amplification of stimulated Raman scatter (SRS), where laser light scatters off self-generated electron plasma waves. Recently, we have incorporated an SRS model that supports two electron plasma waves at different frequencies (and hence two reflected light waves) into the laser beam propagation code pF3d.\footnote{C. H. Still, \textit{et al}. IFSA Proceedings (2009)} This enables simulations which include a secondary SRS wave matched to the least damped mode in the LEH as determined by post-processing radiation-hydrodynamics simulations. Such a simulation also entails calculating the off-resonant amplification. Thus, we have enhanced the SRS model in pF3d to improve the accuracy of modeling the off-resonant response. We report on the enhancements to the SRS model, implementation, and the results of two SRS group simulations with one mode the primary SRS backscatter and one matched in the LEH plasma. LLNL-ABS-414822 prepared by LLNL under contract DE-AC52-07. [Preview Abstract] |
Thursday, November 5, 2009 10:30AM - 10:42AM |
TO5.00006: Nonlinear Plasma Wave Behavior in Multiple Dimensions Relevant to Stimulated Raman Scattering Jay Fahlen, Ben Winjum, Thomas Grismayer, Viktor Decyk, Warren Mori Recent particle-in-cell (PIC) simulations (L. Yin \textit{et al}., PRL \textbf{99}, 265004 (2007) and B. Winjum's poster) of stimulated Raman scattering (SRS) in multiple dimensions indicate that plasma wavefront bowing and localization are important potential nonlinear saturation mechanisms. We present here the results of detailed PIC simulations in which an external, ponderomotive impulse driver generates finite-width plasma waves. These simulations allow careful study of wave behavior over a wide range of parameters. We find that local, kinetic damping effects operate in conjunction with wavefront bowing to localize large-amplitude plasma waves along their axis. The simulations are performed using an electrostatic PIC code, and also a PIC code using the Darwin approximation to solve for the electric and magnetic fields without radiation. This work was supported by DOE under Grant Nos. DE-FG52-03-NA00065, DE-FG52-06NA26195, and DE-FG02-03ER54721. [Preview Abstract] |
Thursday, November 5, 2009 10:42AM - 10:54AM |
TO5.00007: STUD Pulses: Spike Train of Uneven Duration and Delay for the Control of Laser-Plasma Instabilities in ICF, IFE and HEDLP Bedros Afeyan It is possible to stop the runaway growth of parametric instabilities by breaking up multi-nanosecond laser pulses into a train of spikes on the psec time scale whose amplitudes, durations and inter-spike delays are design parameters adjusted to keep laser plasma instabilities (LPI) from undergoing too many e-foldings (which would be determined experimentally, under given plasma conditions). This new approach also addresses multiple overlapping laser beam (direct drive) and intercone beam crossing (indirect drive) effects which are major concerns for all options for ICF and IFE to date. With STUD pulses, multi-beam interactions are kept under control or disallowed outright by interleaving in time the spikes in different beams. Most importantly, STUD pulses usher in the possibility of the use of green (0.53 $\mu $m) or even 1 $\mu $m radiation as ICF drivers since LPI will now be actively controlled. STUD pulses can be implemented on the NIF by just changing the front end with no need for changes to the amplifier chain. Finally, in the million or more (wide bandwidth) fiber laser approach to IFE in the future, STUD pulses are a natural mechanism to ensure LPI control since the speckle patterns of overlapped randomly timed beams will be naturally independent from spike to spike with very long recurrence times, guaranteeing linear and modest growth in time of instabilities. [Preview Abstract] |
Thursday, November 5, 2009 10:54AM - 11:06AM |
TO5.00008: A 3D, Parallel, Solution-Adaptive Model for Radiative Shocks Kenneth Powell, Paul Drake, James Holloway, Bart Van der Holst, Smadar Karni, William Martin, Eric Myra, Igor Sokolov, Quentin Stout, G. Toth In this talk, a radiation hydrodynamics code for simulating radiative shocks will be described. The high-level validation problem for the code is one in which a 1 ns, 4 kJ laser pulse irradiates a Be disk, driving a shock into a Xe-filled plastic tube. The radiative precursor to the shock heats the wall of the tube, so that the there is a complex interaction among the shock driven by the ablated material from the wall, the laser driven shock, and the Be-Xe interface. The code is three-dimensional, solution-adaptive, and parallel. The radiation transport model in the current code is based on gray diffusion; work is underway to support higher-fidelity radiation transport models. The methodology used in the code and preliminary results of simulations will be presented. [Preview Abstract] |
Thursday, November 5, 2009 11:06AM - 11:18AM |
TO5.00009: Kinetic simulation of neutron production in a deuterium z-pinch Dale Welch, David Rose, William Stygar, Ramon Leeper Fully kinetic particle-in-cell (PIC) modeling of a deuterium gas puff z-pinch can provide insight into the physical mechanisms for D-D fusion neutron production. Experiments with 15-MA current pinches on the Z accelerator have suggested that the dominant neutron-production mechanism is thermonuclear. The non-linear evolution of the Rayleigh Taylor instability as the pinch coalesces on axis, however, induces large electric fields capable of driving a significant number of high energy ions similar to that reported in dense plasma focus machines where measured ion spectra exhibit power-law dependence. In order to gain further insight, we have performed 2D PIC simulations of deuterium z-pinch implosions that permit non-Maxwellian particle distributions, finite mean-free-path effects, self-consistent anomalous resistivity, and charge separation. The calculated neutron yields largely follow the predicted thermonuclear I$^{ 4}$ current scaling [A. L. Velikovich, et. al, Phys. of Plasmas 14, 022701 (2007)], but also exhibit the power law ion distribution and significant non-thermal neutron production. We will discuss both production mechanisms and impact on the scaling of neutron yield at higher current. [Preview Abstract] |
Thursday, November 5, 2009 11:18AM - 11:30AM |
TO5.00010: Surface Roughness Reduction on Divinylbenzene Foam Shells Jon Streit, John Karnes, Brian Motta, Nicole Petta Inertial fusion energy targets for the Naval Research Laboratory's High Average Power Laser Program require millimeter-scale, low density foam capsules with a gas permeation barrier and an outer surface roughness less than 50 nm RMS. Divinylbenzene (DVB) foam is a candidate for the capsule wall material, but its porous, open celled surface has been both too rough and difficult to seal. To overcome this difficulty we have repurposed a previously reported dual stage initiator emulsion microencapsulation method, adding an additional step that enhances the surface of the foam capsules. Using both low and high temperature initiators allows the DVB foam to gel in the low temperature stage and a water soluble monomer to be added and polymerized during the high temperature stage without breaking down the emulsion. This method forms a submicron skin that covers the open celled DVB foam surface, resulting in a superior substrate for gas permeation barrier deposition. [Preview Abstract] |
Thursday, November 5, 2009 11:30AM - 11:42AM |
TO5.00011: Progress toward an air-dried HAPL target capsule John Karnes, Jonathan Streit, Brian Motta, Nicole Petta, Shannan Downey, Michael Droege NRL's High Average Power Laser (HAPL) Program works to design an inertial fusion energy power plant based on a modular laser system and direct drive targets. One task of this project is the development of a coated low density foam shell to contain the cryogenic deuterium-tritium (DT) fuel. An economic model of the HAPL fusion power plant requires that these foam capsules must be produced at a cost of less than 25$\not{c} $ each for the plant to produce competitively priced energy. Capsule materials of interest are open celled structures with submicron-scale pores. If allowed to ``air-dry,'' capillary forces at air-liquid interfaces within the pores destroy the capsule's morphology. Critical point drying, a costly production step, is used to avoid this problem. We present recent work towards developing a low density HAPL capsule prototype that avoids this processing step by synthesizing a low density material that survives ``air-drying.'' [Preview Abstract] |
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