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 GO5: Hohlraum Physics |
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Chair: Mark Herrmann, Sandia National Laboratories Room: Reunion C |
Tuesday, November 18, 2008 9:45AM - 9:57AM |
GO5.00001: Laser Propagation Effects and Symmetry at Hohlraum Temperatures of Order 100eV S.R. Goldman, N.M. Hoffman, G.A. Kyrala, E.S. Dodd, H.A. Rose Radiation emission experiments from capsules in NIF-0.7 scale vacuum hohlraums at the Omega laser frequently indicate shapes that are more oblate (with respect to the hohlraum symmetry axis) than simulations.\footnote{G. Kyrala et al., BAPS \textbf{52} (16), p. 318 (2007) } This has been attributed to the modeling of laser beams which make relatively small (21\r{ }) angles with that axis. Shape agreement is significantly improved by assuming that the laser beams are statistically scattered through a parametrically controlled algorithm. We have examined the simulations with the LIP post-processor\footnote{ICF Annual Report, LLNL, UCRL-LR-105820-98, p. 13 (1998) } to see whether laser plasma instabilities could account for the scattering. Due to the low laser intensities, instabilities are relatively weak and appear to be confined to regions close the initial capsule and hohlraum wall boundaries; nevertheless the pF3D code\footnote{S.H. Glenzer et al., Nature Physics \textbf{3}, 716 (2007)} should be useful in evaluating their role in laser propagation modification. In addition, we have estimated the effect of the experimental phase plate speckle patterns on stable beam scattering. [Preview Abstract] |
Tuesday, November 18, 2008 9:57AM - 10:09AM |
GO5.00002: Hohlraum Energetics with a Plastic-Lined Laser Entrance Hole S.P. Regan, T.C. Sangster, D.D. Meyerhofer, W. Seka, R.L. McCrory, C. Stoeckl, V.Yu. Glebov, N.B. Meezan, L.J. Suter, D.J. Strozzi, E.A. Williams, W.L. Kruer, O.S. Jones, D.A. Callahan, M.D. Rosen, O.L. Landen, S.H. Glenzer, C. Sorce, B.J. MacGowan The coupling of laser energy into x-ray drive, suprathermal electrons, stimulated Brillouin scattering (SBS), stimulated Raman scattering (SRS), and the two-plasmon-decay (2\textit{$\omega $}$_{pe})$ instability was investigated on the OMEGA Laser System for a Au hohlraum having a plastic (CH) lined laser entrance hole (LEH). Forty beams smoothed with phase plates and arranged in three cones irradiated gas-filled targets with a 13.5-kJ shaped laser pulse (PS26). The observed increases in SRS, 3/2\textit{$\omega $}, and hard x-ray production (\textit{h$\upsilon $} $>$ 20 keV) at the end of the laser drive and the corresponding decrease in the peak $T_{r}$ are attributed to local increases in the hohlraum $n_{e}$ caused by the expansion of the CH LEH liner. Quantitative comparisons with hydrodynamic 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] |
Tuesday, November 18, 2008 10:09AM - 10:21AM |
GO5.00003: Detailed simulations of x-ray drive in gas-filled hohlraums with plastic-lined laser entrance holes N.B. Meezan, K. Widmann, C. Sorce, L.J. Suter, F. Girard, S.P. Regan Recent experiments on the OMEGA laser facility examined x-ray drive in gas-filled gold hohlraums with and without plastic- (CH-) lined laser entrance holes (LEH's). We use simulations with the multi-physics code \textsc{hydra} to examine the role of the LEH liner as a sink for laser and x-ray energy. The hohlraums were filled with a hydrocarbon gas mixture to 4.5\% of the critical density, resulting in hydrodynamic evolution very similar to that seen in simulations of NIF ignition hohlraums. Comparisons with DANTE measurements show excellent agreement for hohlraums with unlined LEH's. HYDRA over-predicts the flux from hohlraums with lined LEH's by less than 10\%. H\textsc{ydra} also reproduces the M-band $\left(2 \textrm{keV} < \epsilon < 5 \textrm{keV}\right)$ flux at the peak of the laser pulse but under-predicts the M-band during the rising edge of the pulse. [Preview Abstract] |
Tuesday, November 18, 2008 10:21AM - 10:33AM |
GO5.00004: Effect of NLTE emissivity models on NIF ignition hohlraum power requirements L. Suter, S. Hansen, M. Rosen, P. Springer, D. Callahan It's well known that the NLTE atomic physics model can significantly affect the power requirements and plasma conditions in ignition hohlraums. This is because the emissivity(Te,ne) is a significant factor in determining the time dependent coronal temperature of the hot blow-off plasma filling ignition hohlraums which, in turn, determines the total energy stored in that coronal plasma at any instant. In this talk we present best estimates of NLTE emissivity using the SCRAM model, including the range of uncertainty, and compare them with the emissivity of the model used to design NIF ignition hohlraums and set the NIF pulse shape. We then present pulse shapes derived from hohlraum simulations using an atomic physics model that approximates the SCRAM emissivities. We discuss the differences in coronal energetics and show how this affects the pulse shape and decreases the peak power requirement. Finally, we present design simulations of potential NIF-commissioning scaling experiments that could distinguish among emissivity models. Prepared by LLNL under Contract DE-AC52-07NA27344. [Preview Abstract] |
Tuesday, November 18, 2008 10:33AM - 10:45AM |
GO5.00005: Observation of Large Electric Fields on Laser-Irradiated Gold Hohlraums due to Cavity Positive Charging R. Petrasso, C. Li, F. Seguin, J. Frenje, M. Manuel, D. Casey, N. Sinenian, P. Amendt, R. Town, O. Landen, A. Nikroo, C. Back, J. Kilkenny, J. Knauer, J. Soures We report on the first observation of an electric field up to $\sim $ 10$^{9 }$V/m, due to cavity positive charging, in laser-irradiated gold hohlraums. A complete time sequence of time-gated, monoenergetic proton radiographs, acquired simultaneously and separately for both 15 and 3 MeV protons, was obtained during a 1.6-ns interval (the hohlraum was driven for $\approx $ 1ns). The radiographs made with different proton energies provide complementary but distinctly different information about the evolution of the fields, thus creating a comprehensive picture of the entire field evolution. These new measurements will advance our understanding of hohlraum physics and fields, and are also likely to have important consequences for inertial confinement fusion and basic laboratory high-energy density physics. This work was performed in part at the LLE National Laser User's Facility (NLUF), and was supported in part by US DOE, LLNL, LLE and the Fusion Science Center at Univ. Rochester. [Preview Abstract] |
Tuesday, November 18, 2008 10:45AM - 10:57AM |
GO5.00006: Wall-shaped hohlraum influence on symmetry and energetics in gas-filled hohlraums Veronique Tassin, Franck Philippe, Stephane Laffite, Laurent Videau, Marie-Christine Monteil, Bruno Villette, Philippe Stemmler, Sophie Bednarczyk, Emilie Peche, Benoit Reneaume, Christian Thessieux On the way to the LMJ completion, achieving ignition with 40 quads in a 2-cone configuration will be attempted as a first step. Theoretical investigation of a rugby-shaped hohlraum shows energetics optimization and a better symmetry control compared to a cylindrical hohlraum [1]. We recently conducted experiments on the Omega laser facility with 3 different wall-shaped methane-filled hohlraum configurations. We present here the experimental results. Energetics benefits are shown for reduced wall area hohlraums. The wall-shaped hohlraum influence on time-dependent radiation symmetry is also discussed. For the 3 gas-filled hohlraums configurations, we compare the foamball early-time radiographs, the D2Ar-filled capsule time-integrated images and the core self-emission images. [1] M. Vandenboomgaerde, Phys. Rev. Lett., 99, 065004 (2007). [Preview Abstract] |
Tuesday, November 18, 2008 10:57AM - 11:09AM |
GO5.00007: A Simulation of the NIF Ignition Campaign S.V. Weber The National Ignition Campaign comprises a series of experiments to tune the laser pulse shape, implosion symmetry, and target parameters to achieve conditions required for ignition. We have performed a simulated campaign to test the NIC strategy and build infrastructure. A blue team carried out the campaign, including specifying targets, laser pulses and diagnostic configuration, analyzing simulated data and making tuning choices. The actual NIF shot setup protocol was employed. A red team, representing nature, generated mock data for the NIF diagnostic suite using a computer code employing a hidden physics model. Anticipated noise and uncertainties were incorporated. Examples of data are Dante scope voltage traces and gated microchannel plate x-ray images. The campaign included energetics, symmetry, and shock timing shots. Following the tuning process, several ignition shots were attempted. This exercise has lead to improvements in the NIC tuning strategy. [Preview Abstract] |
Tuesday, November 18, 2008 11:09AM - 11:21AM |
GO5.00008: Assessing the effect of asymmetry during the foot of the NIF laser pulse on capsule margin Jose Milovich, Michael Edwards, Harry Robey Capsule margin is the ratio of capsule energy at ignition time relative to the minimum energy required for ignition. Margin can be determined by four parameters, peak velocity, the amount of instability growth between the DT fuel and ablator, fuel entropy, and hot spot shape. Drive asymmetry during the foot of the laser pulse is typically thought of as introducing distortion in the hot spot shape at ignition time thus impacting margin. A more subtle effect that has not previously been considered is that it leads to asymmetry in shock velocity and timing, increasing entropy above the ideal case. This effect is particularly important during the first ~ 2ns of the laser pulse which largely sets the arrival time of the first shock at the inner surface of the DT ice. In this paper we use post processed results of 2D rad hydro simulations to show how drive asymmetry affects margin during the first ~ 2ns of the laser pulse and use the results to set early time symmetry requirements. [1] D. Clark, S. Haan J. Salmonson, Physics of Plasmas 15,056305 (2008) [Preview Abstract] |
Tuesday, November 18, 2008 11:21AM - 11:33AM |
GO5.00009: Radiation energy transport through hydrodynamically evolving slits J.M. Foster, P. Graham, M. Taylor, A. Moore, C. Sorce, A. Reighard, S. Maclaren, P. Young, G. Glendinning, B. Blue, C. Back, J. Hund Radiation transport through enclosed spaces with inwardly moving walls is a key component of the physics of laser-heated hohlraums. It arises in the cavity itself (where inward motion of the wall results in late-time stagnation of dense plasma on the hohlraum axis), and also in the laser-entry and diagnostic holes (where an understanding of hole-closure is important to hohlraum design and the interpretation of diagnostic data). To understand these phenomena better, we have carried out a series of experiments at the Omega laser facility. A laser-heated hohlraum is used to illuminate linear and annular slits machined in samples of solid-density tantalum and low-density, tantalum-oxide foam. Measurements of the transmitted energy are made indirectly (by measuring the temperature rise of a ``calorimeter'' hohlraum) and directly (by measuring the emission from the slit component, using a target in which the calorimeter hohlraum was omitted). The hydrodynamics is investigated by self-emission and absorption (backlighting) x-ray imaging of the closing slits. Simulations (using a 2-D Eulerian hydrocode) reproduce the overall energetics, the detail of the deceleration shock and axial stagnation region at the centre of the slit, and the complex shock interactions that occur at corners of the slits. [Preview Abstract] |
Tuesday, November 18, 2008 11:33AM - 11:45AM |
GO5.00010: Drive Symmetry Measurements with Ignition Relavent Conditions using Large Scale, Be, Thin Shell Capsules on the Omega Laser Robert Kirkwood, E. Dewald, J.M. Edwards, J. Milovich, D.H. Kalantar, O.L. Landen, S.R. Goldman, M. Schmitt One technique to obtain symmetric ignition implosions on NIF is to measure the symmetry of the hohlraum radiation drive as a function of time by monitoring the shape of thin shell capsules by x-ray backlit imaging. Experiments at the Omega laser facility provided brightly backlit images of 0.7-scale Be capsules doped with 2{\%} Cu under NIC foot conditions by using a 1ns pulse shape for drive and backlighter beams. 16 images of the imploding shell were recorded on each shot with a 4.7 keV (Ti), foil backlighter between 6.6 and 7.4 ns. Separate shots varied the fraction of energy in the cones and the total drive energy. The shell was observed to have a significant P2 distortion when the inner cone power was low, and increasing the inner cone power was shown to produce a symmetric shell with P2 near zero. The results will be compared with simulation of the expected shell distortion to verify the sensitivity of the technique. This Work was performed under the auspices of the U.S. DOE by Lawrence Livermore Lab under contract No. DE-AC52- A27344, LLNL-ABS-405480. [Preview Abstract] |
Tuesday, November 18, 2008 11:45AM - 11:57AM |
GO5.00011: Using view factor analysis to guide multi-parameter hohlraum optimization for NIC Cliff Thomas, John Edwards To achieve ignition, a NIC capsule requires a high degree of x-ray drive uniformity. In theory, this is achieved by the careful balance of several parameters including laser power, the distribution of laser power in each laser cone, the hohlraum geometry, the case-capsule ratio, laser pointing and focal spot size. Since the parameter space is large, it is difficult to explore using full-physics models. To circumvent this difficulty, this study considers view factors - a rapid vehicle for exploring the available parameter space - to identify sub-regions for more detailed analysis. Combining view factors with a global optimization routine, the NIC parameter space is thoroughly explored, and `symmetry islands' are found. These islands are explained, and the balance between energy efficiency and drive symmetry is discussed. [Preview Abstract] |
Tuesday, November 18, 2008 11:57AM - 12:09PM |
GO5.00012: Re-emit experiments in NIF-scale vacuum hohlraums for foot symmetry tuning of indirect drive ignition implosions on the NIF Eduard Dewald, Jose Milovich, Cliff Thomas, John Edwards, Ogden Jones, Robert Kirkwood, Nobuhiko Izumi, Otto Landen In indirect drive ignition experiments on the National Ignition Facility (NIF), tuning of the symmetry of the hohlraum radiation drive for the first 2 ns will be assessed by the re-emit technique [1] which measures the instantaneous x-ray drive asymmetry based on soft (800-1200 eV) x-ray imaging of the re-emission of a high-Z sphere surrogate capsule. We performed multi-view re-emit symmetry experiments in 60{\%} scale NIF ignition hohlraums using NIF-like 2 laser cone illumination at 90-110 eV NIF foot radiation temperatures at the Omega facility [2]. We measured radiation symmetry sensitivity to inner/outer beams power balance and we assessed the residual radiation asymmetry of the patched diagnostic holes and missing laser beams required for soft x-ray imaging based on orthogonal polar images. The experimental data accuracy validated that required for NIF. Finally, we will discuss the design of a 90{\%} scale experiment planned for Omega and the implications of all results to our NIF symmetry tuning strategy. [1] N. Delamater, G. Magelssen, A. Hauer, \textit{Phys. Rev. E} \textbf{53}, 5241 (1996). [2] E.L. Dewald, \textit{et. al.,} submitted to Rev. Sci. Instrum. [Preview Abstract] |
Tuesday, November 18, 2008 12:09PM - 12:21PM |
GO5.00013: The NIF Ignition Target 3D Point Design Ogden S. Jones, Michael M. Marinak, Jose L. Milovich, Debra A. Callahan We will discuss progress that has enabled turn around times of about a day for 3D calculations of the NIF ignition point design targets using the Hydra radiation hydrodynamics code. These are integrated calculations of the laser-heated hohlraum and the capsule (either a DT-filled ignition capsule or any of several types of diagnostic capsules). Each laser beam is set up to have its own power versus time and pointing, which enables an assessment of random errors in power and pointing. Low-mode (Legendre mode 8 or less) capsule surface perturbations and capsule centering error can also be included. By running problems on up to 1024 processors and carefully controlling the time step we can achieve run times of about 30 hours. We show results for capsule designs with plastic or beryllium ablators. [Preview Abstract] |
Tuesday, November 18, 2008 12:21PM - 12:33PM |
GO5.00014: Application of variably-doped ablators to a single-sided drive ICF hohlraum Roger Vesey, Stephen Slutz Symmetry control has been computationally demonstrated for a z-pinch driven double-ended hohlraum requiring 18 MJ of pulse-shaped x-ray energy and yielding 500 MJ in two-dimensional integrated hohlraum and capsule simulations [1]. A single-sided drive hohlraum for this capsule may allow efficiency gains by reducing the hohlraum wall area, avoids pinch power imbalance and mistiming issues associated with two-pinch systems, and allows a simpler and more efficient pulsed-power accelerator design. A major obstacle is the large inherent odd Legendre mode (P$_{1}$, P$_{3}$, etc.) asymmetry present with single-sided drive. Hohlraum shaping and mode-selective shields may be used to lower inherent asymmetries; here we investigate the use of in-depth variable doping of the capsule ablator [2] to compensate for the residual drive asymmetries. 2D LASNEX design simulations will be presented to evaluate the required doping levels and resulting source energy requirements. [1] R. A. Vesey \textit{et al}., Phys. Plasmas \textbf{14}, 056302 (2007). [2] S. A. Slutz \textit{et al.}, Phys. Rev. Lett. \textbf{99}, 175001 (2007). [Preview Abstract] |
Tuesday, November 18, 2008 12:33PM - 12:45PM |
GO5.00015: Application of variably-doped ablators to NIF capsules Stephen Slutz, Roger Vesey 2D LASNEX simulations indicate that polar angle- and depth-dependent doping of inertial fusion capsule ablators can effectively compensate for radiation drive asymmetries [1]. We present simulations of a NIF capsule design [2] with variable in-depth doping to compensate for low order radiation asymmetry modes. Such symmetry compensated capsules could allow modifications to the laser pointing within the NIF hohlraum that increase the radiation asymmetry, but reduce the potential for deleterious laser plasma interactions. [1] S. A. Slutz, R. A. Vesey, and M. C. Herrmann, Phys. Rev. Lett. \textbf{99}, 175001 (2007). [2] S. W. Haan, M.C. Herrmann, T.R. Dittrich et al, Phys. Plasma 12, 056316 (2005). [Preview Abstract] |
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