Bulletin of the American Physical Society
49th Annual Meeting of the Division of Plasma Physics
Volume 52, Number 11
Monday–Friday, November 12–16, 2007; Orlando, Florida
Session JO3: Compression and Burn II |
Hide Abstracts |
Chair: George Kyrala, Los Alamos National Laboratory Room: Rosen Centre Hotel Salon 9/10 |
Tuesday, November 13, 2007 2:00PM - 2:12PM |
JO3.00001: High-Areal-Density Cryogenic D$_{2}$ Implosions on OMEGA T.C. Sangster, V.N. Goncharov, P.B. Radha, V.A. Smalyuk, R. Betti, R.S. Craxton, J.A. Delettrez, D.H. Edgell, V.Yu. Glebov, D.R. Harding, J.P. Knauer, F.J. Marshall, R.L. McCrory, P.W. McKenty, D.D. Meyerhofer, S.P. Regan, W. Seka, S. Skupsky, J.M. Soures, C. Stoeckl, B. Yaakobi, J.A. Frenje, R.D. Petrasso, D. Shvarts The validation of direct-drive ignition target designs on OMEGA requires the demonstration of both 1-D burn and 1-D areal density (\textit{$\rho $R}) up to the point of mix truncation with cryogenic fuel on an adiabat of $\le $4 and a peak implosion velocity of $\sim $3.5 $\times $ 10$^{7}$ cm/s. We report here on the demonstration of 1-D \textit{$\rho $R} in a series of cryogenic D$_{2}$ implosions with a fuel adiabat of $\sim $2. The targets consisted of a thick CD ablator (10-\textit{$\mu $}m wall) and a fuel layer of $\sim $95 \textit{$\mu $}m of D$_{2}$. The inner-surface roughness of the ice was $\sim $2-\textit{$\mu $}m rms. With an 18-kJ decaying shock drive pulse with a peak intensity of 5 $\times $ 10$^{14}$ W/cm$^{2}$, the $\langle $\textit{$\rho $R}$\rangle $ was 202 mg/cm$^{2}$ (95{\%} of 1-D). The thick CD ablator mitigates hot electron preheat from the two-plasmon-decay instability in hydrogen---by design, no hydrogen reaches the quarter-critical density surface. Future experiments will focus on areal density performance at higher implosion velocities. This work was supported by the U.S. DOE Office of ICF under Cooperative Agreement DE-FC52-92SF19460. [Preview Abstract] |
Tuesday, November 13, 2007 2:12PM - 2:24PM |
JO3.00002: Using Radiation Preheat to Improve Shell Stability in OMEGA Implosions P.B. Radha, J.P. Knauer, T.C. Sangster, V.N. Goncharov, I.V. Igumenschev, R. Betti, R. Epstein, D.D. Meyerhofer, S. Skupsky Preheat of imploding shells from coronal photons in direct-drive implosions has been previously proposed to shape the adiabat in the shell and reduce ablative Rayleigh--Taylor growth rates during acceleration.\footnote{ S. E. Bodner \textit{et al.}, Phys. Plasmas \textbf{5}, 1901 (1998).} OMEGA cryogenic and warm plastic designs with Si-doped ablators are studied using one- and two-dimensional simulations. The effect on compression, single-mode growth rates, and shell distortions are examined. Areal density, which primarily depends on the inner-shell adiabat, is a sensitive measure of preheat of the inner fuel. Simulation results will be compared with observations of areal densities in OMEGA implosions. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement DE-FC52-92SF19460. [Preview Abstract] |
Tuesday, November 13, 2007 2:24PM - 2:36PM |
JO3.00003: Transport of Energetic Electrons Produced from Two-Plasmon Decay in the 1-D Hydrodynamic Code \textit{LILAC} J.A. Delettrez, V.N. Goncharov, P.B. Radha, C. Stoeckl, A.V. Maximov, T.C. Sangster, J.A. Frenje, D. Shvarts The effect of two-plasmon-decay electrons on the implosion of cryogenic targets has been the subject of intense scrutiny at the Laboratory for Laser Energetics. Preheat of the fuel caused by these electrons can reduce the maximum areal density attainable at stagnation. The electrons are created at the quarter-critical surface when a threshold depending on laser intensity and local thermal electron scale length is attained. The fraction of laser energy absorbed 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 Maxwellian with a temperature scaling inferred from the measurement of hard x rays. The electrons are transported with a multigroup diffusion model in which the free-streaming electrons are treated by a modified $P_{2}$ model. Simulation results from warm plastic and cryogenic implosions are compared with the following experimental diagnostics: the hard-x-ray temporal and time-integrated 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 DE-FC52-92SF19460. [Preview Abstract] |
Tuesday, November 13, 2007 2:36PM - 2:48PM |
JO3.00004: X-Ray Spectral Measurements of Cryogenic Capsules Imploded by OMEGA F.J. Marshall, J.P. Knauer, T.C. Sangster, J.A. Delettrez, P.W. McKenty, R. Epstein, V.N. Goncharov, B. Yaakobi A set of absolutely calibrated, x-ray imaging systems have been used to measure the emergent x-ray spectra from cryogenic D$_{2}$- and DT-filled capsules imploded by the OMEGA UV Laser System. The imaging systems include both pinholes and Kirkpatrick--Baez microscopes, all dispersed by transmission gratings. The shapes of the observed spectra allow for inference of the core electron temperature (\textit{kT}$_{e})$ and in selected cases the surrounding main-fuel-layer areal density (\textit{$\rho $R}$_{fuel})$. The latter determination is dependent on the assumed temperature and density in the fuel layer and hence can only place bounds on the quantity \textit{$\rho $R}$_{fuel}$. Comparisons of these measurements with both one- and two-dimensional hydrocode simulations are used in part to evaluate the performance of these implosions. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement DE-FC52-92SF19460. [Preview Abstract] |
Tuesday, November 13, 2007 2:48PM - 3:00PM |
JO3.00005: Radiative Transport Modeling Relevant to Cryogenic Implosion Simulation and Diagnosis R. Epstein, J.A. Delettrez, V.N. Goncharov, J.P. Knauer, P.W. McKenty, F.J. Marshall, P.B. Radha, S.P. Regan, H. Sawada, B. Yaakobi The design of OMEGA cryogenic implosion experiments relies in part on modeling radiative preheat, one method of improving the hydrodynamic stability of the imploding shell. Diagnosing the core temperature and shell density near peak compression relies in part on modeling shell-absorption spectroscopy. Important elements of our modeling, including atomic physics approximations, high-density physics, transport methods, and multidimensional hydrodynamic effects are identified, and their impact on the accuracy of the radiative transport simulation and on the interpretation of the measured spectra are considered. Simulation results are compared with observed spectra from both the ablative preheat and the core emission phases of the implosions. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC52-92SF19460. [Preview Abstract] |
Tuesday, November 13, 2007 3:00PM - 3:12PM |
JO3.00006: Nonlocal Ion-Heat Transport and Viscosity in ICF Implosions Using a Quasi-Monte Carlo Approach 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 computer models. During this time, a local treatment of heat conduction and viscosity is not valid. To investigate the effect of these long mean-free-path ions, two different models (based on Monte Carlo and kinetic techniques) have been developed to treat the nonlocal ion transport, and they have been applied to the modeling of experiments on the OMEGA laser. This presentation will focus on the quasi-Monte-Carlo approach in which ions are tracked through the plasma, and energy and momentum are deposited nonlocally. The following paper (D. Li) will discuss the quasi-kinetic approach. Comparison of the results will be presented. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement DE-FC52-92SF19460. [Preview Abstract] |
Tuesday, November 13, 2007 3:12PM - 3:24PM |
JO3.00007: Modeling Ion Heat Transport in ICF Targets D. Li, V.N. Goncharov, I.V. Igumenshchev, S. Skupsky This talk will describe the kinetic model used to treat the nonlocal ion heat flux and viscosity in ICF implosions. The model is based on the solution of a simplified Boltzman equation using the Krook approximation. Such an approach was successfully used to calculate nonlocal electron conduction.\footnote{ V. N. Goncharov, Phys. Plasmas \textbf{13}, 012702 (2006).} The model is implemented in the 1-D hydrocode \textit{LILAC}. The results of simulations and comparison with the experimental data will be presented. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement DE-FC52-92SF19460. [Preview Abstract] |
Tuesday, November 13, 2007 3:24PM - 3:36PM |
JO3.00008: Investigation of Shock Heating and Heat-Front Penetration in Direct-Drive Targets Using Absorption Spectroscopy H. Sawada, S.P. Regan, P.B. Radha, R. Epstein, V.N. Goncharov, D. Li, D.D. Meyerhofer, V.A. Smalyuk, T.C. Sangster, B. Yaakobi, R.C. Mancini Time-resolved Al 1$s$--2$p$ absorption spectroscopy was used to diagnose direct-drive, shock-heated, and compressed planar targets having nearly Fermi-degenerate predicted plasma conditions ($T_{e} \quad \sim $ 10 to 30 eV, $n_{e} \quad \sim $ 1 to 6 $\times $ 10$^{23}$ cm$^{-3})$. A 50-\textit{$\mu $}m-thick CH foil with a buried Al tracer layer was irradiated with 10$^{14}$ to 10$^{15 }$W/cm$^{2}$, and $\sim $1.5 keV x~rays from a point source Sm backlighter were transmitted through the drive foil. The measured absorption spectra were modeled with the atomic physics code PrismSPECT to infer $T_{e}$ and $n_{e}$. The shock heating and heat-front penetration were simulated with the 1-D hydrocode \textit{LILAC}, using a flux-limited or nonlocal transport model. Shock-heating observations are consistent with \textit{LILAC} for the lower drive intensity, but there is evidence of preheat for the higher one. The timing of the heat-front penetration is consistent with a time-dependent flux limiter. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement DE-FC52-92SF19460. [Preview Abstract] |
Tuesday, November 13, 2007 3:36PM - 3:48PM |
JO3.00009: The Effect of Target Mounts in Direct-Drive Implosions on OMEGA I.V. Igumenshchev, V.N. Goncharov, F.J. Marshall, M.J. Bonino, P.W. McKenty, D.D. Meyerhofer, T.C. Sangster Two types of target mounts are currently employed in direct-drive-implosion experiments on OMEGA. A silicon-carbon stalk glued normally to the target surface is used in the case of gas-filled plastic capsules, and a C-mount with four spider silks glued to the target surface is used in cryogenic implosion experiments. We use the 2-D radiation hydrodynamic code \textit{DRACO}\footnote{ P. B. Radha \textit{et al}., Phys. Plasmas \textbf{12}, 032702 (2005).} to study the effects of target mounts in the implosions of capsules. The capsules are $\sim $430-\textit{$\mu $}m radius and driven by nanosecond-time-scale laser pulses with 10 to 25 kJ of total energy. The simulations indicate that the stalk mount can introduce a significant distortion to the hot spot in plastic implosions. The results of these simulations are compared with x-ray experimental images. The glue spots in the C-mount have been found to not significantly perturb cryogenic implosions, and the simulated neutron yield is only marginally affected. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement DE-FC52-92SF19460. [Preview Abstract] |
Tuesday, November 13, 2007 3:48PM - 4:00PM |
JO3.00010: Multidimensional Numerical Investigation of NIF Saturn PDD Designs with 3-D Laser Ray Tracing P.W. McKenty, R.S. Craxton, S. Skupsky, J.A. Marozas, T.J.B. Collins, A. Shvydky, D. Keller, D.D. Meyerhofer, R.L. McCrory The Laboratory for Laser Energetics continues to validate the use of the NIF and the LMJ in the x-ray-drive configuration for direct-drive-ignition experiments. Progress in this area indicates that polar direct drive (PDD) is a viable and attractive option for achieving ignition on these megajoule-class laser systems. Recent work has focused on the implementation of the Saturn PDD illumination scheme, which, employing an equatorial CH ring as a plasma lens, attempts to minimize target perturbations due to the absence of the equatorial beams in the x-ray-drive laser configuration. This paper will examine the implementation of the standard ``all-DT'' direct-drive-ignition design with a fixed CH equatorial ring. Previous work\footnote{ R. S. Craxton \textit{et al}., Phys. Plasmas \textbf{12}, 056304 (2005).} employed 2-D hybrid \textit{SAGE}--\textit{DRACO} calculations and indicated minimal performance degradation from 1-D results. We will report on recent 2-D hydrodynamic \textit{DRACO} simulations, examining the effects of the Saturn PDD illumination as modeled with fully integrated 3-D ray-trace models. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement DE-FC52-92SF19460. [Preview Abstract] |
Tuesday, November 13, 2007 4:00PM - 4:12PM |
JO3.00011: Initial Polar-Direct-Drive Designs to Optimize Neutron Yields on the NIF R.S. Craxton, A.M. Cok, P.W. McKenty Polar-direct-drive (PDD) designs are proposed for producing symmetric implosions of thin-shell, DT-gas--filled targets leading to high fusion neutron yields for neutron diagnostic development. The designs can be used as soon as the National Ignition Facility (NIF) is operational as they work with indirect-drive phase plates. Two-dimensional simulations using the hydrodynamics code \textit{SAGE} have shown that good low-mode uniformity can be obtained by means of appropriately chosen combinations of defocusing and pointing of the beams, including pointing offsets of individual beams within some of the NIF laser beam quads. The optimizations have been carried out for targets with total laser energies ranging from 350 kJ to 1.5 MJ, enabling the optimum defocusing and pointing parameters to be determined through interpolation for any given laser energy in this range. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement DE-FC52-92SF19460. [Preview Abstract] |
Tuesday, November 13, 2007 4:12PM - 4:24PM |
JO3.00012: Single-Beam Smoothing Requirements for Wetted-Foam, Direct-Drive NIF Ignition Target Designs T.J.B. Collins, J.A. Marozas, P.W. McKenty, P.B. Radha, S. Skupsky, J.D. Zuegel Wetted-foam, direct-drive target designs are a path to high-gain experiments on the National Ignition Facility (NIF). Previous studies have shown that reduction of single-beam nonuniformity is central to target performance of designs incorporating solid CH ablators.\footnote{ P. W. McKenty\textit{ et al}., Phys. Plasmas \textbf{8}, 2315 (2001).} It has also been shown that at 1 MJ, even a wetted-foam target with a low IFAR and low acceleration-phase instability requires a minimum of two-dimensional (2-D) smoothing by spectral dispersion (SSD)\footnote{ S. Skupsky\textit{ et al}., J. Appl. Phys. \textbf{66}, 3456 (1989).} for ignition.\footnote{ T. J. B. Collins\textit{ et al}., Phys. Plasmas \textbf{14}, 056308 (2007).} We show the results of 2-D simulations indicating that this is also the case for 1.5-MJ, wetted-foam, direct-drive NIF target designs. Some possible avenues for single-beam smoothing in the absence of 2-D SSD will be briefly presented. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement DE-FC52-92SF19460. [Preview Abstract] |
Tuesday, November 13, 2007 4:24PM - 4:36PM |
JO3.00013: Alternative Laser-Speckle--Smoothing Schemes for NIF Direct-Drive-Ignition Designs J.A. Marozas, J.D. Zuegel, T.J.B. Collins The National Ignition Facility (NIF) in its current configuration has smoothing by spectral dispersion (SSD) in only one spatial dimension with a single FM modulator. Such smoothing has been shown to be insufficient in providing adequate uniformity for directly driven targets. It may be possible, however, to attain adequate smoothing using different options within the NIF's capabilities. The motivation is to shoot direct-drive or polar-direct-drive (PDD) targets before the full 2-D SSD system is operational. Two-dimensional \textit{DRACO} simulations of PDD targets, utilizing 3-D ray-trace subroutines, will be used to investigate the feasibility of alternative laser-speckle--smoothing options such as multiple FM modulators in 1-D, chirped pickets and defocused beams. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement DE-FC52-92SF19460. [Preview Abstract] |
Tuesday, November 13, 2007 4:36PM - 4:48PM |
JO3.00014: The Application of Shock Ignition to Various High Gain Target Concepts. L.J. Perkins, K. LaFortune, A. Miles, L. Divol, G. Logan, R. Betti Shock-ignition, a new approach [1] for high gain ignition and burn is being studied for several ICF target concepts: \textit{(1) High gain cryogenic IFE targets, driven by lasers or heavy ions, } \textit{(2) High fusion yield targets for DOE NNSA applications, } \textit{(3) Simple, non-cryogenic single shell gas targets. } Such concepts could be assessed on NIF following achievement of indirect-drive ignition. In contrast to conventional hotspot ignition, the assembly and ignition phases are separated by imploding a high mass shell at low velocity using a direct drive pulse of modest energy. The assembled fuel is then separately ignited by a strong, spherical shock driven by a late-time high intensity laser spike, timed to reach the axis 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 for the same kinetic energy in the shell. Like fast ignition, shock ignition can achieve high gains at low drive energy, but has the advantages of needing only a single laser with less demanding timing and focusing. \newline [1] R.Betti, C.Zhou, K.Anderson, L.J.Perkins, A.Solodov, \textit{Phys Rev. Lett. }\textbf{\textit{98}}$, (2007)$. [Preview Abstract] |
Tuesday, November 13, 2007 4:48PM - 5:00PM |
JO3.00015: Ten times higher laser ablation efficiency by nonlinear force driven plasma blocks Heinrich Hora, George Miley A significant anomaly at ps. TW laser interacting with plasma was observed based on the suppression of relativistic self-focusing [1,2]. Highly directed low temperature plasma blocks (pistons) are generated by acceleration by the nonlinear (ponderomotive) force. This directly converts optical energy into hydrodynamic motion with little thermal loss due to unavoidable collisions. Instead of the usual 5{\%} ablation efficiency for plasma compression using thermalization, this direct energy conversion mechanism permits 50{\%} ablation efficiency as predicted at spherical compression for fusion [3]. From detailed experiments and computations [2] it can be concluded that irradiated DT fuel shells even may not need the initially pre-irradiation generally assumed [3]. The directivity of the imploding shells permits various options for fusion reactions in the compressed plasma. \newline \newline [1] H. Hora, J. Badziak et al. Opt. Commun. 207, 333 (2002). \newline [2] H. Hora, J. Badziak et al. Phys. Plasmas 14, 072701 (2007). \newline [3] H. Hora, Nucl. Inst. and Methods 144, 17 (1977). [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700