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 NO5: Compression and Burn I |
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Chair: Richard Petrasso, Massachusetts Institute of Technology Room: Reunion C |
Wednesday, November 19, 2008 9:45AM - 9:57AM |
NO5.00001: Low-Adiabat Polar-Drive Implosion Experiments on OMEGA F.J. Marshall, R.S. Craxton, R. Epstein, V.Yu. Glebov, V.N. Goncharov, J.P. Knauer, P.W. McKenty, D.D. Meyerhofer, P.B. Radha, T.C. Sangster, W. Seka, S. Skupsky, V.A. Smalyuk, J.A. Frenje, C.K. Li, R.D. Petrasso, F.H. S\'eguin Low-adiabat, directly driven implosion experiments are being performed on OMEGA using 40 beams oriented nearer two poles of the target (polar drive), emulating the current configuration of the beams of the NIF. Targets are all non-cryogenic, D$_{2}$-gas-filled CH capsules. Shaped pulses keep the main fuel layer of the target (CH shells in these experiments) at a low adiabat (2 to 3) during the compression phase. In contrast to the design of a directly driven, polar-drive-ignition target for the NIF, these experiments are performed with the same beam profile and pulse shape for all beams and thus are not optimized. Nevertheless, the measurements of the target performance, when compared to 2-D hydrocode simulations, can be used to extrapolate to the optimized designs for the NIF. Framed x-ray imaging (both self emission and backlit) is used to diagnose implosion symmetry, while nuclear and particle measurements are used to diagnose compressed core conditions. 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] |
Wednesday, November 19, 2008 9:57AM - 10:09AM |
NO5.00002: Recent Experimental Results from Cryogenic Implosions on OMEGA T.C. Sangster, V.N. Goncharov, P.B. Radha, R. Betti, T.R. Boehly, V.Yu. Glebov, S.X. Hu, R.L. McCrory, P.W. McKenty, D.D. Meyerhofer, W. Seka, V.A. Smalyuk, J.A. Frenje, R.D. Petrasso, D. Shvarts The implosion performance of energy-scaled cryogenic D$_{2}$ and DT targets on the 60-beam OMEGA laser is important for understanding the physics of highly compressed fuel and the validation of ignition designs for the NIF. Recent experiments have demonstrated good performance using a multi-shock drive that has been tuned based on cryogenic cone-in-shell targets. Fuel areal densities are now consistently exceeding 80{\%} of the 1-D prediction, while the yields are between 10{\%} and 20{\%} of 1-D predictions. These results demonstrate the benefit (and necessity) of an independent shock-timing platform. This talk will present the latest implosion performance results and potentially show the first cryogenic-fuel-core radiographs using a short pulse beam from the new OMEGA EP Laser Facility. 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] |
Wednesday, November 19, 2008 10:09AM - 10:21AM |
NO5.00003: Modeling Observables to Diagnose Areal Density in OMEGA Implosions P.B. Radha, V.N. Goncharov, T.C. Sangster, R. Betti, J.A. Delettrez, S.X. Hu, D.D. Meyerhofer, S. Skupsky, V.A. Smalyuk, C. Stoeckl, J.A. Frenje, C.K. Li, R.D. Petrasso, D. Shvarts Areal density, \textit{$\rho $R}, depends on laser absorption, shock timing, shell preheat, and equation-of-state of shell material. Secondary proton spectra are used to diagnose \textit{$\rho $R} during neutron production. The observed neutron-production rates are typically truncated compared to simulations. This results in a preferential sampling of areal density, leading to differences in inferred values of \textit{$\rho $R} between simulation and experiment. Simulations of low-adiabat, direct-drive implosions on the OMEGA laser are post-processed to obtain spectra after accounting for this effect. Comparisons are made with inferred \textit{$\rho $R} values from implosions irradiated with laser pulse shapes at different intensities and differing adiabat profiles in the shell. Possible reasons for deviations are discussed. This work was supported by the U.S. D.O.E Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC52-08NA28302. [Preview Abstract] |
Wednesday, November 19, 2008 10:21AM - 10:33AM |
NO5.00004: Simulation and Optimization of Backlit Images of Cryogenic Implosions on OMEGA R. Epstein, V.A. Smalyuk, W. Theobald, F.J. Marshall, J.A. Delettrez, V.N. Goncharov, S.X. Hu, P.W. McKenty, P.B. Radha Cryogenic implosions on OMEGA are to be imaged using short-pulse, K-shell emission-line backlighters driven by the OMEGA EP laser. Backlighter composition is chosen so that the emission-line energies occur where the opacity profiles of the imploded cores will provide a measurable range of optical depth near the time of peak compression. At the same time, the specific intensity of the backlight must be optimized to overcome the core self-emission. The OMEGA EP short-pulse capability provides a backlight exposure time short enough to discern the overall shell integrity and convergence, as well as the shell structure resulting from the low-order hydrodynamic effects of drive nonuniformity caused by target offset and ice-layer nonuniformity. Simulation results are compared with backlight spectra and backlit implosion images obtained from the first experiments of this kind on the OMEGA EP system. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC52-08NA28302. [Preview Abstract] |
Wednesday, November 19, 2008 10:33AM - 10:45AM |
NO5.00005: Two-Dimensional Investigation of Neutron-Yield Performance in Direct-Drive, Low-Adiabat D$_{2}$ Implosions on OMEGA S.X. Hu, P.B. Radha, J.A. Marozas, R. Betti, T.J.B. Collins, R.S. Craxton, J.A. Delettrez, D.H. Edgell, R. Epstein, V.N. Goncharov, I.V. Igumenshchev, F.J. Marshall, R.L. McCrory, P.W. McKenty, D.D. Meyerhofer, S.P. Regan, T.C. Sangster, S. Skupsky, V.A. Smalyuk, D. Shvarts Neutron yields of direct-drive, low-adiabat (\textit{$\alpha $} $\approx $ 2 to 3) cryogenic D$_{2}$ target implosions on OMEGA have been systematically investigated using 2-D, radiation hydrodynamics \textit{DRACO} simulations. We have focused on the neutron-yield degradation caused by initial target offset, ice-layer roughness, and low-mode laser-irradiation nonuniformities. Simulations provide a reasonably good guide to understanding experimental neutron-yield degradation for thin-shell (5{\-}\textit{$\mu $}m) cryogenic implosions. The neutron yields are found to be sensitive to the phase between the target offset and the ice-layer roughness. For 10-\textit{$\mu $}m-thick-shell implosions, the experimental yield is generally lower than what low-mode \textit{DRACO} simulations predict, for which high-mode studies will also be presented. This work was supported by U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC52-08NA28302. [Preview Abstract] |
Wednesday, November 19, 2008 10:45AM - 10:57AM |
NO5.00006: Experimental Investigation of Thermal-Transport Models in Direct-Drive Targets Using X-Ray Absorption Spectroscopy H. Sawada, S.P. Regan, V.N. Goncharov, P.B. Radha, D. Li, S.X. Hu, R. Epstein, D.D. Meyerhofer, V.A. Smalyuk, T.C. Sangster, B. Yaakobi, R.C. Mancini Shock-wave heating and heat-front penetration in direct-drive planar targets were measured using time-resolved Al 1$s$--2$p$ absorption spectroscopy to validate thermal-transport models in the 1-D hydrocode \textit{LILAC}. A CH foil with a buried Al layer was irradiated with peak intensities of 10$^{14}$ to 10$^{15}$ W/cm$^{2}$. The measured spectra were modeled with an atomic physics code to infer $T_{e}$ and \textit{$\rho $} ($T_{e} \quad \sim $ 10 to 40 eV and \textit{$\rho $} $\sim $ 3 to 11 g/cm$^{3})$ in the Al layer. Strong shock waves and isentropic compression were studied. Nonlocal and flux-limited ($f$ = 0.06) models accurately predict the measurements while the shock transits the foil. $T_{e}$ was lower than predicted at late times of the drive and was attributed to reduced radiative heating caused by lateral heat flow in the corona. Evidence of energetic electron preheat was masked by these 2-D effects. 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] |
Wednesday, November 19, 2008 10:57AM - 11:09AM |
NO5.00007: Creating and Mining a Large Database of 2-D NIF Implosion Simulations Brian Spears, C. Cerjan, S. Haan, S. Hatchett, D. Wilson Iterating to ignition success on NIF will require capsule and drive specifications that give a reasonable \textit{a priori} chance of ignition and robust diagnostics that allow a physical understanding of the experimental implosion dynamics. To supply a basis for our physical understanding we have focused on a measure of ignition margin as a function of 4 performance parameters --- fuel velocity, fuel entropy, mix, and hot-spot radial rms. To this end, we have created a large database of 2-D implosion simulations corresponding to points covering the input parameter space defined by the capsule and drive specifications. Each simulation is post-processed to supply diagnostic signatures, with and without modeled errors, that constrain the associated diagnostic experiment, and the associated four performance parameters. Finally, a data mining algorithm is applied to extract relationships among diagnostic features and performance parameters. These correlations are then used to establish experimental design requirements and rectify non-optimal implosion behavior. LLNL-ABS-405318. This work performed under the auspices of Lawrence Livermore National Security, LLC, (LLNS) under Contract DE-AC52-07NA27344. [Preview Abstract] |
Wednesday, November 19, 2008 11:09AM - 11:21AM |
NO5.00008: Simulation of NIF Ignition Shock Timing Diagnostics Rick Olson, David Bradley, Peter Celliers, Harry Robey In previous Omega experiments, time-resolved measurements of hohlraum radiation temperature were made via interferometer measurement of quartz shock velocity.$^{1}$ In the present work, the data of Ref. 1 are used to confirm the validity of two new ``synthetic diagnostics'' (rad-hydro code postprocessor simulations of the diagnostics). The synthetic VISAR provides a simulated streaked image showing time-resolved fringe shifts of a line-imaging velocity interferometer.$^{2}$ The simulated VISAR ``data'' can be unfolded to provide a recording of the shock velocity within the interior of an optically-transparent material (eg., quartz in the Ref 1 data or liquid deuterium in the NIF ignition campaign). The synthetic SOP provides a simulated intensity-time image of a streaked optical pyrometer.$^{3}$ The simulated SOP ``data'' can be unfolded to provide shock breakout times and time-resolved shock front intensity. These two synthetic diagnostics include a variety of realistic experimental and diagnostic uncertainties. Both were developed for use in a NIF simulated ignition campaign, and were utilized in a series of simulated ignition campaign ``shots'' in which the shocks were empirically tuned so as to converge to a successful simulated NIF ignition attempt. 1. R. E. Olson \textit{et al}., Rev. Sci. Instrum. 77, 10E523 (2006). 2. P. M. Celliers \textit{et al}., Rev. Sci. Instrum. 75, 4916 (2004). 3. J. A. Oertel \textit{et al}., Rev. Sci. Instrum. 70, 803 (1999). [Preview Abstract] |
Wednesday, November 19, 2008 11:21AM - 11:33AM |
NO5.00009: Estimate of expected shot-to-shot shock timing variations on NIF and their impact on implosion margin Harry Robey Ignition implosions planned for the National Ignition Facility (NIF) require a laser pulse shape with a carefully tuned series of steps, which launch a series of shocks into the DT fuel. The relative timing of these shocks must be tuned to better than +/- 100ps to maintain the fuel on a sufficiently low adiabat. Shot-to-shot variations in shock timing will result from a large number of sources. Variations in target parameters (ablator layer thicknesses, densities, dopant concentrations, etc.) that are within required specifications but below the measurement resolvability will give rise to measurable variations in shock timing. Similarly, in-spec variations in the laser drive (timing and levels of steps in the laser power history) will cause shock-timing variations. To estimate the impact of these variations on shock timing, a large number of single and multiple variable sensitivity studies have been performed. Variations in shock-timing measurable quantities are related to corresponding entropy variations to quantify their allowable limits and their impact on implosion margin. [Preview Abstract] |
Wednesday, November 19, 2008 11:33AM - 11:45AM |
NO5.00010: X-ray Thomson scattering for characterization of ICF capsule implosions Siegfried Glenzer, Brian Spears, Paul Neumayer, Andrea Kritcher, Tilo Doeppner, Otto Landen We have developed accurate x-ray Thomson scattering techniques to measure the physical properties of dense plasmas produced in high-energy density physics experiments. Powerful penetrating x-ray sources are employed to probe these short-lived hot dense states of matter with electron densities in the range of solid density and higher. The back-scattering spectrum accesses the non-collective Compton scattering regime, which provides accurate diagnostic information on the temperature, density and ionization states. The forward scattering spectrum has been shown to measure the collective plasmon oscillations. Applying these techniques for the characterization of the short-lived imploding capsule conditions in inertial confinement fusion experiments suggest that future experiments can yield the in-flight capsule adiabat and entropy. [Preview Abstract] |
Wednesday, November 19, 2008 11:45AM - 11:57AM |
NO5.00011: Analysis of directly driven OMEGA experiments to assess the effect of 3He on capsule implosion and yield J.H. Cooley, H.W. Herrmann, J.M. Mack, C.S. Young, J. Langenbrunner, D.C. Wilson, S.C. Evans, T.J. Sedillo, G.A. Kyrala, C.J. Horsefield, D.W. Drew, W.J. Garbett, E.K. Miller, V. Yu Glebov Los Alamos has been performing experiments to better understand the anomalous effects of 3He on capsule yield demonstrated by MIT[1]. Experiments were performed on the OMEGA laser at Laboratory for Laser Energetics (LLE) using a 600ps 16kJ square pulse. The targets were 4.9 $\mu$m SiO2 capsules with 1100 $\mu$m diameter. The gas fill 3He was varied with the amount of T fixed. The amount of D was varied in a way to ensure hydrodynamic equivalence of the fully ionized DTHe3 gas. In this paper we present results of modeling these experiments. In particular we evaluate the possible confounding effects of target and drive uncertainties on the interpretation of the results and attempt to assess to what degree the 3He effects diagnostics of interest. We also investigate effects of pressure multipliers on the gas EOS to understand if a poor EOS can lead to the observed behavior. [1] Rygg et. al., Phys. Plasmas 13, 2006 [Preview Abstract] |
Wednesday, November 19, 2008 11:57AM - 12:09PM |
NO5.00012: The Effect of Helium on Burn in Directly Driven Glass Capsules Douglas C. Wilson, George A. Kyrala, John F. Benage, Frederick J. Wysocki, Johan A. Frenje, Vladimir Yu. Glebov, Samuel Roberts, Warren J. Garbett Experiments on the Omega laser confirm the previous observation (Rygg \textit{et al.} (\textit{Phys. Plasmas}, \textbf{13}, 052702 (2006)) of an abnormal degradation of D+D(n) and D+$^{3}$He(p) yields in hydrodynamically equivalent capsules as the $^{3}$He fraction is increased. The degradation remained using $^{4}$He. These implosions used either 23 kJ of laser energy in a 1000ps square pulse, or 13 kJ in a 600ps pulse, onto 900 micron diameter, $\sim $ 4.3 micron thick glass shells filled with 10 atm of deuterium or hydrodynamically equivalent mixtures with He. Measured ion temperatures would be the same for all mixtures in hydrodynamically equivalent capsules. For the 1000ps implosions they are. But for 600ps implosions the ion temperature increases with $^{3}$He concentration, showing a deviation from equivalency. Work supported by US DOE/NNSA, performed at LANL, operated by LANS LLC under Contract DE-AC52-06NA25396. [Preview Abstract] |
Wednesday, November 19, 2008 12:09PM - 12:21PM |
NO5.00013: Spectroscopic diagnosis of OMEGA direct-drive low-adiabat implosions Ricardo Florido, T. Nagayama, R.C. Mancini, R. Tommasini, J. Delettrez, S.P. Regan, V. Smalyuk We discuss the observation and data analysis of K-shell line spectra from argon-doped deuterium-filled OMEGA direct-drive low-adiabat implosions based on data recorded with streaked crystal spectrometers. The argon line spectrum is primarily emitted at the collapse of the implosion thus providing a spectroscopic diagnostic of core implosion conditions. The observed spectra includes resonance and satellite transitions in H-, He- and Li-like Ar ions thus covering a broad photon energy range from 3200 eV to 4200 eV with a spectral resolution power of appoximately 500. Both optically thick and thin lines are simultaneously modeled, including line overlapping and Stark-broadening effects. The spectroscopic analysis yields the details of temperature and density time-histories in the compressed core. [Preview Abstract] |
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