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 YO6: Hohlraum Physics and HEDP |
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Chair: Eduard Dewald, Lawrence Livermore National Laboratory Room: Rosen Centre Hotel Salon 5/6 |
Friday, November 16, 2007 9:30AM - 9:42AM |
YO6.00001: Usefulness of a Rugby-shaped hohlraum in a Laser M\'egaJoule (LMJ) 40-quad configuration G. Malinie, M. Vandenboomgaerde, J. Bastian, D. Galmiche, S. Laffite, S. Liberatore The LMJ setup will consist of 60 quads in a 3-cone configuration, at angles 33.2$^{\circ}$, 49$^{\circ}$ and 59.5$^{\circ}$. First ignition attempts in indirect drive are planned to be made on the way to the completion of the full facility, with only 40 quads in a 2-cone configuration, at angles 33.2$^{\circ}$ and 49$^{\circ}$. By analytic considerations, we show that in a 40-quad configuration, the angular location of the hohlraum outer irradiating ring, as seen from the capsule, must be closer to the laser entrance hole than with the full LMJ. The use of a Rugby-shaped hohlraum instead of a cylinder therefore allows to keep a correct symmetry while reducing the wall surface, which improves the global energetic efficiency of the target. Simplified 2D numerical simulations of Rugby hohlraums are presented, achieving a yield of about 30 MJ with our 1.215 mm-radius, CH-uniform-ablator capsule. These results suggests this kind of hohlraum might be an interesting candidate for 40-quad ignition experiments. Work on optimizing the present design and refining the numerical simulations is currently pursued. [Preview Abstract] |
Friday, November 16, 2007 9:42AM - 9:54AM |
YO6.00002: Experimental comparison of symmetry in rugby and cylindrical holhraums Franck Philippe, Veronique Tassin, Stephane Laffite, Marie-Christine Monteil, Josiane Bastian, Laurence Lours, Bruno Villette, Philippe Stemmler, Sophie Bednarczyk, Benoit Reneaume, Pascale Di Nicola, Vincent Raffin Recently, holhraum shape optimization has been investigated as a practical way to achieve ignition at lower energy [1][2]. Rugby shaped holhraums theoretically allow better energetic coupling and symmetry control than classical cylinders. As a first step toward an experimental validation of this design, this talk presents the results of experiments on the OMEGA laser facility dedicated to the comparison of symmetry in cylindrical and rugby holhraums. Foamball radiographs and Symcaps emission contours for both type of holhraums are compared to numerical simulation results. \newline \textbf{[1]} M. Vandenboomgaerde \textit{et al.}, accepted by Phys. Rev. Lett. \newline \textbf{[2] }P. Amendt \textit{et al.}, Phys. Plasmas \textbf{14}, 056312 (2007) [Preview Abstract] |
Friday, November 16, 2007 9:54AM - 10:06AM |
YO6.00003: Long pulse gas-filled halfraums on OMEGA for high growth-factor ablative Rayleigh-Taylor experiments Alexis Casner, G. Huser, B. Villette, M. Vandenboomgaerde, D. Galmiche, S. Liberatore, F. Philippe, L. Masse Mitigation of Rayleigh-Taylor instabilities growth is crucial to enhance the performance of LMJ and NIF ignition targets. We recently develop on OMEGA a long-pulse platform in order to experimentally prove two mechanisms invoked for RTI stabilization, i.e the graded-doped ablator [1] and the new laminated ablator concept [2]. We used gas-filled halfraums (1 atm neopentane) and stack up to 20 drive beams along 3 cones to create a 7 ns long radiation drive. The new E-IDI-300 phase plates were associated with 1D SSD and halfraum energetics was validated along P5/P8 axis for backscattering measurements along 2 cones. We will also present the first face-on radiographies for modulated CH(Ge) samples and compare them with FCI2 hydrocodes simulations. Foil thickness optimization based on these simulations allows us to anticipate growth factors up to 500 in optical depth and the experimental emulator designs for [1,2] will be presented. \newline [1] S.W. Haan \textit{et al.}, Phys. Plasmas \textbf{12}, 056316 (2005). \newline [2] L. Masse$.$, Phys. Rev. Lett. 98, 245001 (2007). DPP07 invited talk. [Preview Abstract] |
Friday, November 16, 2007 10:06AM - 10:18AM |
YO6.00004: Tradeoffs of efficiency and symmetry control for z-pinch driven ICF hohlraums R.A. Vesey, M.C. Herrmann, S.A. Slutz, M.E. Cuneo, J.L. Porter Time-dependent symmetry control for a double z-pinch driven hohlraum using only structures within the hohlraum has allowed the symmetric implosion and ignition of a 500 MJ inertial fusion capsule in detailed two-dimensional simulations [1]. The secondary hohlraum surrounding the capsule has a case-to-capsule radius ratio of 3.8, which provides geometric averaging of modes P$_{6}$ and higher, while mode-selective burnthrough shields provide time-dependent control of modes P$_{2}$ and P$_{4}$. The clearest path to improving the hohlraum efficiency and increasing the system energy gain is to decrease the amount of x-ray energy deposited in the hohlraums that surround the imploding z-pinches, which may be achieved by reducing the wall area. This computational study quantifies the tradeoffs between system efficiency and symmetry control for the 500 MJ capsule in reduced case-to-capsule ratio hohlraums and in single-ended (1-pinch) and double-ended (2-pinch) hohlraums. [1] R. A. Vesey \textit{et al}., Phys. Plasmas \textbf{14}, 056302 (2007). [Preview Abstract] |
Friday, November 16, 2007 10:18AM - 10:30AM |
YO6.00005: Time-dependent radiation drive asymmetry compensation of inertial fusion capsules by ablator doping Stephen Slutz, Roger Vesey, Mark Herrmann Ablator doping, the process of adding small amounts of specific materials to tailor the opacity of the ablator, is shown to be an effective means of compensating for radiation drive asymmetries. As an example, an inertial fusion capsule with a beryllium ablator variably doped with gold has been designed to compensate for a P$_{2}$ radiation asymmetry of 20{\%} and still produce nominal fusion yield. In contrast, the same capsule without variable doping, fails when the P$_{2}$ asymmetry exceeds 2{\%}. The technique can compensate time-dependent asymmetries by varying the doping as a function of depth within the ablator. We also show that doping can compensate for high levels of other low order modes, e.g. P$_{1}$, P$_{4}$, and P$_{6 }$radiation asymmetries. [Preview Abstract] |
Friday, November 16, 2007 10:30AM - 10:42AM |
YO6.00006: Laser performance on the National Ignition Facility Michael Shaw, C.A. Haynam, W.H. Williams, C.C. Widmayer, M.A. Henesian, R.A. Sacks, S.N. Dixit, P.J. Wegner, S.T. Yang, B.M. Van Wonterghem The Laser Performance Operations Model (LPOM) [1] was developed to automatically set up, and diagnose the performance of the National Ignition Facility (NIF). LPOM uses the detailed physics model, Virtual Beamline (VBL) [2], for its energetics predictions. We will present comparisons of LPOM predictions with results of a series of laser shots where one beam in a quad was diagnosed at both 1w and 3w with the Precision Diagnostic Station (PDS). The comparisons will include pulse shaping, energetics, frequency conversion, shape timing adjustments, and spatial fluence in both the near and far field. An analysis of the shot-to-shot power repeatability for ignition pulses will also be presented. \newline [1] M. Shaw, et al, Optical Engineering, 43, 2885-2895 (2004). \newline [2] C. Haynam, et al, Applied Optics Journal Vol. 46, No. 16/1 June 2007. [Preview Abstract] |
Friday, November 16, 2007 10:42AM - 10:54AM |
YO6.00007: NIF power balance performance modeling and testing D.H. Kalantar, S.N. Dixit, C.A. Haynam, N.C. Mehta, M.J. Shaw, C.C. Widmayer, W.H. Williams A model for predicting power balance performance on the National Ignition Facility (NIF) has been developed. The Power Balance Model (PBM) uses Laser Performance Operations Model (LPOM) runs with statistical variations in laser performance beam-to-beam and quad-to-quad. We have used this model to predict power balance performance for full NIF ignition shots. These predictions will be presented and compared with results from a series of single quad laser shots where one beam was diagnosed at 3w with the Precision Diagnostic Station (PDS) [1]. The shot-to-shot power repeatability from these PDS tests is consistent with the predicted power balance performance, and with the performance requirements for the ignition campaigns. \newline \newline [1] C. Haynam, et al, International Conference on Inertial Fusion Sciences and Applications, 2007. [Preview Abstract] |
Friday, November 16, 2007 10:54AM - 11:06AM |
YO6.00008: Calculating response of NIF ignition capsules to random 3D errors O.S. Jones, J.L. Milovich, D.A. Callahan, S.W. Haan, C.C. Widmayer To estimate the probability of ignition for a given ICF capsule design, an error budget has been developed in which an allowable range of values for each important parameter is defined. We generally categorize the deviations of each parameter from its ideal value as 1D (affecting the implosion velocity and fuel entropy) or 3D (affecting the amount of distortion of the imploded core at time of maximum compression). In this work we focus on estimating the effect of various 3D errors. To do this we carried out numerous 3D calculations of ignition hohlraums and capsules with imposed errors in laser beam pointing, laser power, capsule centering, etc. The calculations were done using the Hydra radiation hydrodynamics code. The large size and number of required simulations presented new challenges for completing the studies in a reasonable amount of time. We will quantify the effect of each type of 3D random error and assess its impact on the overall error budget rollup. [Preview Abstract] |
Friday, November 16, 2007 11:06AM - 11:18AM |
YO6.00009: Measurements of the non-uniformities seeded by NIF ignition capsule ablator materials P.M. Celliers, D.J. Erskine, S.T. Prisbrey, D.G. Braun, J.B. Richards, C.M. Sorce, G.W. Collins, R.J. Wallace, O.L. Landen, A. Nikroo Current NIF ignition target designs contain the DT fuel inside spherical capsules made of either Cu-doped Be or high density C (HDC). Both candidate materials are polycrystalline, and are expected to respond anisotropically to the initial compression wave of the NIF compression sequence. Estimates of the amplitudes of the non-uniformities seeded by each type of ablator suggest that these capsules should remain stable during the subsequent implosion; however, experiments are needed to verify these estimates. We describe experiments designed to measure shock front perturbations induced by the microscopic polycrystalline non-uniformities of these two ablator materials. The measurement method employs a time-resolved two-dimensional imaging VISAR illuminated by a 2 ps laser pulse, which captures spatial variations in the velocity across the shock front transmitted through the ablator. The measurement is carried out over an 800 $\mu $m field of view with relative velocity sensitivity $\Delta $V/V $\sim $ 10$^{-4}$, and over perturbation wavelengths in the range from 3-4 $\mu $m to 50 $\mu $m. [Preview Abstract] |
Friday, November 16, 2007 11:18AM - 11:30AM |
YO6.00010: Overview and Recent Results from the HyperV Plasma Gun F. Douglas Witherspoon, Andrew Case, Sarah Messer, Richard Bomgardner, Michael Phillips, David van Doren, Raymond Elton, Ilker Uzun-Kaymak We present an overview of research at HyperV to develop high velocity dense plasma jets for application to fusion and HEDP. The approach uses symmetrical pulsed injection of high density plasma into a coaxial EM accelerator having a cross-section tailored to prevent formation of the blow-by instability. Two development paths are followed to accomplish this injection step: we compare large arrays of capillary discharges to sparkgaps arranged in a toroidal configuration. Experiments on three test fixtures are described: a 2pi configuration with 64 capillary injectors, a 32 injector prototype gun designed to drive rotation in the Maryland MCX experiment, and a second gun using 112 sparkgap electrodes for injection. Data is presented from visible light spectroscopy, fast optical imaging, Rogowski coils, pressure probes, Bdot probes, photodiodes, and a laser interferometer. Ballistic pendulum tests indicate plasma jets with mass 160 micrograms at 70 km/s have been achieved with plasma density above $10^{15}~cm^{-3}$. [Preview Abstract] |
Friday, November 16, 2007 11:30AM - 11:42AM |
YO6.00011: Numerical Simulations of Hypervelocity Plasma Jets M.W. Phillips, F.D. Witherspoon, A. Case, S.J. Messer, T.P. Hughes, D.R. Welch, I.N. Bogatu, S.R. Galkin, J.S. Kim Numerical simulations with comparisons to experiments of hypervelocity plasma jets in development at HyperV Technologies Corp. are presented. The focus will be on the new plasma jet designed to drive rotation in the University of Maryland MCX experiment. Performance of coaxial plasma jets is typically limited by the blow-by instability. Extensive numerical modeling with the Mach 2 code was used in the optimization of the electrode shapes in order to reduce tendencies to blow-by, resulting in a tapered design. To achieve maximum performance each stage of the pulse discharge, including armature formation, acceleration and detachment from the inner electrode, and transport of the plasma blob must be optimized. Experiments have so far demonstrated that plasma blobs of 160 $\mu $grams can be accelerated to 70 km/sec consistent with simulations. Results will also be presented of simulations using the LSP PIC code to study the microphysics of plasma acceleration in more detail. [Preview Abstract] |
Friday, November 16, 2007 11:42AM - 11:54AM |
YO6.00012: Hyper-Velocity C60-Fullerene Plasma Jets for Disruption Mitigation and HEDP I.N. Bogatu, S.A. Galkin, J.S. Kim ITER needs a reliable disruption mitigation technique with real-time capability. The basic approach is to convert the plasma energy density ($\sim $1 GJ in 840 m$^{3})$ into radiation power within 1 ms and increase the electron density by two orders of magnitude all over the plasma cross section to suppress the runaway electrons avalanche. Impurity injection is the principle solution, but once the impurity atoms are ionized in the thin outer layer of tokamak plasma they can no longer penetrate the confining magnetic field unless they have high velocity. We present the concept of producing and using hyper-velocity high-density C60-fullerene plasma jets to penetrate into the core tokamak plasma and deliver the necessary mass. We show that plasma slug model indicates that, by using a capacitive driver of 3 MJ, a C60-fullerene jet of 2.5 g can reach 30 km/s and penetrate half minor radius of ITER plasma. The heavy ion component leads to a high Mach number of the high density (10$^{17}$ cm$^{-3})$ plasma jet making it an attractive candidate for HEDP studies. [Preview Abstract] |
Friday, November 16, 2007 11:54AM - 12:06PM |
YO6.00013: Inclusion of radiation transport and EOS ionization tables in Hybrid-PIC simulations of plasma jets Peter Hakel, Bob Clark, Tom Hughes, Chris Mostrom, Igor Golovkin, Pamela Woodruff, Joseph J. MacFarlane We report on the progress in plasma simulations using the hybrid particle-in-cell (PIC) code LSP. Recently added modeling capabilities include the effects of ionization and radiation. Transport of radiation is treated in two dimensions using the multigroup diffusion approximation. In addition to free-free opacities, we account for the atomic bound states (i.e., line and bound-free radiation) and plasma self-emission and absorption in modeling of the plasma optical properties. The energy in the radiation field is coupled to the plasma through the absoprtion and emission terms in the plasma energy equation. We use the PROPACEOS equation-of-state (EOS) tables that take into account ionization and other non-ideal effects for the given chemical composition. Gray and multigroup radiation fluxes escaping the plasma are extracted and visualized for diagnostic and engineering purposes. We applied the recently enhanced LSP code to modeling of the plasma jet accelerator experiments at HyperV. [Preview Abstract] |
Friday, November 16, 2007 12:06PM - 12:18PM |
YO6.00014: Hybrid PIC Simulations of Particle Dynamics in Coaxial Plasma Jet Accelerators Carsten Thoma, Thomas Hughes, Dale Welch, Peter Hakel We describe the results of 1D and 2D simulations of plasma jet accelerators using the particle-in-cell (PIC) code Lsp. Previous studies of 1D cartesian simulations have shown that ion particle dynamics at the plasma-vacuum interface depend critically on the local Hall parameter, which is strongly dependent on electron temperature. In a coaxial accelerator with finite transverse dimensions, large transverse ion motions, predicted at moderate Hall parameters in 1D, can lead to ion loss to the walls. The results of 2D $r-z$ jet simulations are described and compared with the 1D cartesian results. The effects of particle loss and ablation at the wall are considered, as are electron heating mechanisms at the plasma-vacuum interface, including radiation losses. We will apply the results to the plasma jet experiments underway at HyperV Technologies Corp. [Preview Abstract] |
Friday, November 16, 2007 12:18PM - 12:30PM |
YO6.00015: 3D Simulations of the ``Keyhole'' Hohlraum for Shock Timing on NIF H.F. Robey, M.M. Marinak, D.H. Munro, O.S. Jones Ignition implosions planned for the National Ignition Facility (NIF) require a pulse shape with a carefully designed series of steps, which launch a series of shocks through the ablator and DT fuel. The relative timing of these shocks must be tuned to better than +/- 100ps to maintain the DT fuel on a sufficiently low adiabat. To meet these requirements, pre-ignition tuning experiments using a modified hohlraum geometry are being planned. This modified geometry, known as the ``keyhole'' hohlraum, adds a re-entrant gold cone, which passes through the hohlraum and capsule walls, to provide an optical line-of-sight to directly measure the shocks as they break out of the ablator. In order to assess the surrogacy of this modified geometry, 3D simulations using HYDRA [1] have been performed. The drive conditions and the resulting effect on shock timing in the keyhole hohlraum will be compared with the corresponding results for the standard ignition hohlraum. [1] M.M. Marinak, et al., Phys. Plasmas 8, 2275 (2001). [Preview Abstract] |
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