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 UO5: Compression and Burn |
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Chair: Richard Town, Lawrence Livermore National Laboratory Room: Hanover CDE |
Thursday, November 5, 2009 2:00PM - 2:12PM |
UO5.00001: Shock-Timing Measurements in Directly Driven Spherical Inertial Confinement Fusion Targets T.R. Boehly, V.N. Goncharov, W. Seka, D.E. Fratanduono, M.A. Barrios, S.X. Hu, J.A. Marozas, T.C. Sangster, D.D. Meyerhofer, D.G. Hicks, P.M. Celliers The timing of multiple shock waves in an inertial confinement fusion (ICF) target is critical to its performance. A series of experiments at the Omega Laser Facility used velocity interferometry to measure shocks in directly driven warm and cryogenic targets. Multiple spherical shocks were observed propagating in plastic and liquid deuterium. We report the measured shock velocities and shock coalescence times and compare them to simulations by hydrodynamic codes. 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 5, 2009 2:12PM - 2:24PM |
UO5.00002: Multiple-Picket Cryogenic Target Designs and Performance for OMEGA and the National Ignition Facility V.N. Goncharov, T.C. Sangster, T.R. Boehly, R.L. McCrory, D.D. Meyerhofer, P.B. Radha, V.A. Smalyuk, S. Skupsky, J.A. Frenje, R.D. Petrasso Low-adiabat cryogenic-target-compression experiments are currently performed on the OMEGA laser. Multiple-picket designs have several advantages over the continuous-drive pulses. First, as shown in recent shock-velocity measurements performed on OMEGA,\footnote{T. R. Boehly \textit{et al.}, Phys. Plasmas \textbf{16}, 056302 (2008).} the shock tuning can be facilitated by replacing the region of gradual intensity rise in the continuous-pulse designs with three pickets. The required shock-timing accuracy can be achieved in this case by adjusting energies of individual pickets. Second, the main pulse's contrast ratio is reduced from 40 to 100 in the continuous designs to 2 to 5 in multiple-picket designs. The latter are also less susceptible to Rayleigh--Taylor instability since the intensity pickets produce an enhanced adiabat steepening at the ablation front, increasing the ablative stabilization. This talk will summarize details of the multiple-picket designs and modeling validation with the experimental data. 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 5, 2009 2:24PM - 2:36PM |
UO5.00003: Simulation and Analysis of Backlit Images of Cryogenic Implosions on OMEGA R. Epstein, V.A. Smalyuk, F.J. Marshall, J.A. Delettrez, V.N. Goncharov, P.W. McKenty, D.D. Meyerhofer, P.B. Radha, S.P. Regan, T.C. Sangster, W. Theobald Radiographs of cryogenic implosions on OMEGA have been obtained using short-pulse backlighters driven by the OMEGA EP laser. Computer simulations of an implosion and its x-ray images are used to assess the implosion performance. The radiograph simulation takes into account spatial and temporal resolution, camera spectral response, and the backlighter spectrum. Radial mass distributions are obtained from the radiographs using Abel inversion and the known temperature and density dependence of the free-free opacity of the hydrogen shell. This extends similar analyses of warm-shell radiographs based on the simpler temperature and density dependence of the CH bound-free opacity. The first measurements (which were short of peak compression) are consistent with simulations. More-recent measurements closer to peak compression will be presented. 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 5, 2009 2:36PM - 2:48PM |
UO5.00004: Single- and Multidimensional Robustness Studies of the NIF Ignition Point Design K.S. Anderson, R. Betti, P.Y. Chang, R. Nora, D. Shvarts, M. Fatenejad A robustness study of the NIF ignition point-design target is carried out using hydrodynamically equivalent, all-DT direct-drive targets. The direct-drive targets have similar final mass, kinetic energy, implosion velocity, and adiabat of the indirect-drive point design. The direct-drive target has an equivalent one-dimensional ignition-threshold factor [ITF (1-D)] to the indirect-drive point design. A 1-D sensitivity study of ignition is carried out for various hot-spot conditions, gas pressures, and preheat levels. The hot-spot conditions are varied by changing the thermal conductivity. Two-dimensional studies were performed relating the yield over clean (YOC) of a hydro-equivalent THD surrogate target to fusion gain in the DT ignition target. From these studies is found the minimum THD YOC required to demonstrate ignition in the DT campaign. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement Nos. DE-FC02-ER54789 and DE-FC52-08NA28302. [Preview Abstract] |
Thursday, November 5, 2009 2:48PM - 3:00PM |
UO5.00005: 2-D Simulations of a 1-MJ CH-Foam Ignition Target on the NIF with 0.5 THz of 1-D Multi-FM SSD Bandwidth Using an Analytic Model 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 efficiently by taking advantage of multiple color cycles dispersed across the laser-beam cross section. An analytic SSD model has been enhanced to handle multiple modulators in one or both orthogonal directions. Previously, modeling Multi-FM required an ensemble of simulations that employed random flipping of phase states at every coherence time. The analytic model incorporates the necessary statistical averaging, so only a single simulation is required. An ensemble of random flipping simulations is compared to a simulation of the analytic model. The simulations use the 2-D radiation-hydrodynamics code \textit{DRACO} of a 1.0-MJ CH-foam ignition target on the NIF with 0.5 THz of bandwidth. Dynamic bandwidth reduction is used to increase the angular divergence during the foot of the pulse. 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 5, 2009 3:00PM - 3:12PM |
UO5.00006: Validating Inertial Confinement Fusion (ICF) predictive capability using perturbed capsules Mark Schmitt, Glenn Magelssen, Ian Tregillis, Scott Hsu, Paul Bradley, Evan Dodd, James Cobble, Kirk Flippo, Dustin Offerman, Kimberly Obrey, Yi-Ming Wang, Robert Watt, Mark Wilke, Frederick Wysocki, Steven Batha Achieving ignition on NIF is a monumental step on the path toward utilizing fusion as a controlled energy source. Obtaining robust ignition requires accurate ICF models to predict the degradation of ignition caused by heterogeneities in capsule construction and irradiation. LANL has embarked on a project to induce controlled defects in capsules to validate our ability to predict their effects on fusion burn. These efforts include the validation of feature-driven hydrodynamics and mix in a convergent geometry. This capability is needed to determine the performance of capsules imploded under less-than-optimum conditions on future IFE facilities. LANL's recently initiated Defect Implosion Experiments (DIME) conducted at Rochester's Omega facility are providing input for these efforts. Recent simulation and experimental results will be shown. [Preview Abstract] |
Thursday, November 5, 2009 3:12PM - 3:24PM |
UO5.00007: Design of High-Neutron-Yield Polar-Drive Experiments for Diagnostic Activation on the NIF P.W. McKenty, R.S. Craxton, J.A. Marozas, A.M. Cok, D.D. Meyerhofer, R.L. McCrory, J.D. Kilkenny, A. Nikroo, M.L. Hoppe, M.J. Edwards, D.H. Munro Polar-drive (PD)\footnote{ A. M. Cok, R. S. Craxton, and P. W. McKenty, Phys. Plasmas \textbf{15}, 082705 (2008).} target implosions have been designed for neutron diagnostic development on the NIF. These experiments use thin, room-temperature glass shells filled with low pressures of DT. Initial target implosions on the NIF will produce DT yields in the range of a few 10$^{14}$ neutrons. The predicted yields are consistent with earlier data (10$^{14}$ neutrons at 30 kJ) and recent PD scoping experiments performed on OMEGA. The experiments will use existing x-ray-drive phase plates with judicious repointing and defocusing to drive the implosions as uniformly as possible. Current simulation results indicate that the required yields will be obtained using up to 200-kJ UV light. Large-diameter glass shells ($\sim $1500-\textit{$\mu $}m OD) are under development and fabrication at General Atomics. As tritium and environmental conditions evolve, similar target designs are expected to produce thermonuclear yields approaching 10$^{16}$ neutrons. 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 5, 2009 3:24PM - 3:36PM |
UO5.00008: Polar-Driven Implosions on OMEGA: Observations and Simulations of Low-Mode Perturbations in the Main Fuel Layer and Hot Spot F.J. Marshall, R.S. Craxton, R. Epstein, V.Yu. Glebov, V.N. Goncharov, J.P. Knauer, P.W. McKenty, P.B. Radha, A. Shvydky, J.A. Frenje, C.K. Li, R.D. Petrasso, F.H. S\'{e}guin Low-adiabat, directly driven implosion experiments have been performed on OMEGA using 40 beams in the polar-drive configuration, emulating the configuration of the beams of the NIF. The targets are non-cryogenic, D$_{2}$-gas-filled CH capsules. The areal-density time history of the CH shell and its low-mode perturbations are determined from x-ray radiographs. The conditions of the central fuel region are diagnosed with particle measurements including neutron yield and time history, while low-mode perturbations of the hot spot are determined from framed images of the hot spot's x-ray emission. The observed perturbations are compared with simulations using the 2-D hydrocode \textit{DRACO}. 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 5, 2009 3:36PM - 3:48PM |
UO5.00009: Numerical Investigation of the Effects of Cross-Beam Energy Transfer on the Drive Uniformity of OMEGA Implosions A. Shvydky, P.W. McKenty, J.A. Delettrez, I.V. Igumenshchev, D.H. Edgell, S. Skupsky, R.L. McCrory Evaluation of the scattered light in OMEGA implosions indicates that cross-beam energy transfer caused by stimulated Brillouin scattering (SBS) may explain the observed reduction in the absorbed energy and the details of the spectral shifts in the scattered light. Recently, an \textit{ad-hoc} model of the cross-beam energy transfer has been implemented that scatters light from the central portions of laser beams to reflected, outgoing rays before reaching the critical region. Such a process decreases the total absorption and increases laser deposition nonuniformities. In this paper, using the 2-D radiation-hydrodynamics code \textit{DRACO}, we investigate these two effects and how they affect the implosion uniformity and target performance in OMEGA implosions. High- and low-adiabat plastic and cryogenic implosions are considered, and the simulation results are compared with available OMEGA experiments. 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 5, 2009 3:48PM - 4:00PM |
UO5.00010: Analysis of the Effect of a High-$Z$-doped CH Ablator and Glass Ablators on Preheat and Hard X-Ray Radiation from Two-Plasmon Decay Electrons J.A. Delettrez, J.P. Knauer, V.N. Goncharov, P.B. Radha, C. Stoeckl, A.V. Maximov, J.A. Frenje, D. Shvarts The generation of preheating electrons from two-plasmon decay (TPD) can be mitigated by doping CH shells with Si or Ge or by using glass ablators. Simulations were carried out with a recent model for the source of the TPD fast electrons based on the results of warm-CH-shell implosions. The source energy varies as the threshold parameter $\sim I \quad \times \quad L$/$T_{e}$ at quarter critical. The presence of high-$Z$ dopants increases the temperature, which leads to a decrease in the energy deposited into the fast electrons and a reduction in the resulting preheat. The presence of high-$Z$ dopants, however, leads to higher radiation preheat. This presentation will discuss the effect of the dopants on the fast-electron source and the trade-off between the two forms of preheat in terms of the expected \textit{$\rho $R}'s for both warm-CH and cryogenic implosions. 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 5, 2009 4:00PM - 4:12PM |
UO5.00011: Intensity Dependence of Target Performance in Low-Adiabat, Warm Implosions on OMEGA P.B. Radha, C. Stoeckl, V.N. Goncharov, J.A. Delettrez, T.C. Sangster, R. Betti, R.L. McCrory, D.D. Meyerhofer, S.P. Regan, W. Seka, S. Skupsky, V.A. Smalyuk, D. Shvarts Low-adiabat cryogenic implosions on OMEGA indicate degraded areal densities with increasing intensity. Possible causes include shock mistiming, preheat attributable to coronal fast electrons, and the shadowing of laser illumination caused by silks used to suspend cryogenic targets. Low-adiabat, warm implosion experiments have been designed to study compression in capsule implosions. The adiabat in the shell is set primarily by the foot of the laser pulse and is relatively insensitive to shock mistiming. The plastic ablator in these implosions is similar to the ablator in cryogenic implosions, yielding a very similar density scale length, temperature, and intensity at the quarter-critical surface. Target performance including areal density, yield, bang time, and coronal emission is studied as a function of intensity on OMEGA. Analysis and comparison of experimental observations with 1-D and 2-D simulations will be presented. 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 5, 2009 4:12PM - 4:24PM |
UO5.00012: The effects of laser absorption and mix on direct-drive capsule experiments at OMEGA E.S. Dodd, J.F. Benage, G.A. Kyrala, I.L. Tregillis, D.C. Wilson, F.J. Wysocki, W. Seka, V. Yu. Glebov, J.A. Frenje The yield of an ICF capsule can be affected by the inclusion of high-Z material in the fuel, either as a diagnostic or from hydrodynamic mixing. A series of experiments have been fielded at the OMEGA laser to better understand these effects. The targets are glass shells filled with a mixture of D$_{2}$ and $^{3}$He, and with controlled amounts of a dopant, Ar, Kr, and/or Xe. These targets are then directly driven with a 1.0 ns (0.6 ns) square laser pulse having a total energy of 23 kJ (13.8 kJ), and the data compared with yield and burn-temperature predictions from 1-d radiation-hydrodynamics calculations. However, our calculated yields are typically a factor of two greater than the measured yield, while the calculated burn-weighted temperatures are lower. Estimates for the amount of absorbed laser energy indicate that only 65{\%} to 70{\%} is absorbed. However, our calculations absorb 85{\%} of the energy. The ratio of D$^{3}$He-protons to DT-neutrons also indicates that mixing of shell material has occurred. We will discuss the results of recent 1-d calculations where the incident energy and flux limiter have been varied to match the absorption data. We will also discuss the use of a mix-model to match the charged particle data. Supported by US DOE and LANS, LLC under contract DE-AC52-06NA25396. LA-UR-09-04488 [Preview Abstract] |
Thursday, November 5, 2009 4:24PM - 4:36PM |
UO5.00013: Measurements of Low-Deuterium Surrogates for the Prediction of Ignition Implosion Performance Brian Spears, S. Brandon, D. Clark, C. Cerjan, J. Edwards, O. Landen, J. Lindl, S. Haan, S. Hatchett, J. Salmonson, P. Springer, S. Weber, D. Wilson The National Ignition Campaign (NIC) will use non-igniting ``THD'' capsules to study and optimize the hydrodynamic assembly of the fuel without burn. These capsules are designed to simultaneously reduce DT neutron yield and to maintain hydrodynamic similarity with the DT ignition capsule. We have developed an experimentally observable ignition threshold factor (ITFX) that uses measurements from THD experiments to predict DT ignition implosion performance. The ITFX metric was developed using a database of 2D radhydro simulations of twin DT and THD implosions with a variety of physical failure mechanisms -- drive asymmetry, capsule roughness, continuum mixing, fabrication errors, among others. The ITFX encodes all of these failure mechanisms into a single observable metric. The ITFX metric has also allowed us to develop a capability to estimate the probability of DT capsule ignition based on THD experiments. Prepared by LLNL under Contract DE-AC52-07NA27344. LLNL-ABS-414651 [Preview Abstract] |
Thursday, November 5, 2009 4:36PM - 4:48PM |
UO5.00014: The Use of Tritium Rich Surrogate Capsules with High Deuterium Concentrations to Diagnose Ignition D.C. Wilson, B.K. Spears, S.P. Hatchett II, C.J. Cerjan, P.T. Springer, D.S. Clark, M.J. Edwards, J.D. Salmonson, S.V. Weber, B.A. Hammel, G.P. Grim, H.W. Herrmann, M.D. Wilke The path to ignition at the National Ignition Facility (NIF) relies upon experimentally tuning target conditions. Capsules with mixtures of Tritium, Hydrogen, and Deuterium (THD) can be made hydrodynamically equivalent to 50:50 DT capsules, up to the time when the alpha particle heating becomes significant. Above about 10{\%} deuterium alpha heating, thermal conduction, and electron-ion disequilibria begin to be important. The ion temperature increases and both X-ray and neutron images become larger and more symmetric. As ignition is approached, the fraction of neutrons scattered by the fuel and the burn duration decrease. The high yields from these capsules preclude time resolved X-ray imagers, but allow time resolution of gamma ray emission. The large variation in neutron yield between capsules that would ignite and those that fail improves the ability to predict ignition with 50{\%} deuterium. [Preview Abstract] |
Thursday, November 5, 2009 4:48PM - 5:00PM |
UO5.00015: NIF Ignition Target with High-Density Carbon (HDC) Ablator Darwin Ho, Steven Haan, Jay Salmonson, Lorin Benedict, Juergen Biener, Mark Herrmann High-density carbon as an NIF ignition capsule ablator material has several advantages including a very smooth surface finish and small grain structure. Recent Omega experiments\footnote{P. M. Celliers private communication} show that if the first shock in the ablator is higher than about 6.5 Mbar, which is in the liquid/solid 2-phase region of the carbon phase diagram, then the shock uniformity becomes comparable to that of the Be ablator. Consequently, this is the strength that we adopt for the first shock in our latest HDC capsule design. Using various scanning techniques, the capsule configuration and drive temperature profile are optimized. We describe the 1-D margin and 2-D stability behavior of the optimized point design. [Preview Abstract] |
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