Bulletin of the American Physical Society
56th Annual Meeting of the APS Division of Plasma Physics
Volume 59, Number 15
Monday–Friday, October 27–31, 2014; New Orleans, Louisiana
Session CI1: Direct Drive, Shock and Fast Ignition, Magneto-inertial Fusion |
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Chair: John Edwards, Lawrence Livermore National Laboratory Room: Acadia |
Monday, October 27, 2014 2:00PM - 2:30PM |
CI1.00001: Polar-Drive Experiments at the National Ignition Facility Invited Speaker: M. Hohenberger To support direct-drive inertial confinement fusion (ICF) experiments at the National Ignition Facility (NIF)\footnote{G. H. Miller, E. I. Moses, and C. R. Wuest, Opt. Eng. \textbf{43}, 2841 (2004).} in its indirect-drive beam configuration, the polar-drive (PD) concept\footnote{S. Skupsky \textit{et al}., Phys. Plasmas \textbf{11}, 2763 (2004). } has been proposed. It requires direct-drive--specific beam smoothing, phase plates, and repointing the NIF beams toward the equator to ensure symmetric target irradiation. First experiments testing the performance of ignition-relevant PD implosions at the NIF have been performed. The goal of these early experiments was to develop a stable, warm implosion platform to investigate laser deposition and laser--plasma instabilities at ignition-relevant plasma conditions, and to develop and validate ignition-relevant models of laser deposition and heat conduction. These experiments utilize the NIF in its current configuration, including beam geometry, phase plates, and beam smoothing. Warm, 2.2-mm-diam plastic shells were imploded with total drive energies ranging from $\sim$ 350 to 750 kJ with peak powers of 60 to 180 TW and peak on-target intensities from $4 \times 10^{14}$ to $1.2 \times 10^{15}$ W/cm$^2$. Results from these initial experiments are presented, including the level of hot-electron preheat, and implosion symmetry and shell trajectory inferred via self-emission imaging and backlighting. Experiments are simulated with the 2-D hydrodynamics code \textit{DRACO} including a full 3-D ray trace to model oblique beams, and a model for cross-beam energy transfer (CBET). These simulations indicate that CBET affects the shell symmetry and leads to a loss of energy imparted onto the shell, consistent with the experimental data. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. [Preview Abstract] |
Monday, October 27, 2014 2:30PM - 3:00PM |
CI1.00002: Spherical Strong-Shock Generation for Shock-Ignition Inertial Fusion Invited Speaker: W. Theobald Recent experiments on the Laboratory for Laser Energetics' OMEGA laser have been carried out to produce strong shocks in spherical (SSS) targets. The shocks are launched at pressures of several hundred megabars and reach gigabar pressures upon convergence. The results are relevant to the validation of the shock-ignition (SI) scheme and to the development of an OMEGA experimental platform to study material properties at gigabar pressures. The SSS experiments investigate the strength of the ablation pressure and the hot-electron production at overlapping beam laser intensities of $\sim 3$ to $5 \times 10^{15}$ W/cm$^2$. The measurements demonstrate the generation of convergent shocks launched by an ablation pressure of 300 Mbar, which is crucial to validate the SI concept and to develop an SI target design for the National Ignition Facility. The timing of the x-ray flash from shock convergence in the center of a solid plastic ball target doped with a small amount of Ti is used to infer the shock velocity and pressure in the experiment. It was found that the hot-electron temperature was moderate (\textless 100 keV) and the instantaneous conversion efficiencies of laser energy into hot electrons reached $\sim$ 10\% to 20\% in the intensity spike. The large amount of hot electrons is correlated with an earlier x-ray flash time and a strong increase ($\sim 25 \times$) of the flash intensity. This suggests that hot electrons contribute to the augmentation of the shock strength. This work was supported by the U.S. DOE under DE-NA0001944, DE-FC02-04ER54789.\\[4pt] In collaboration with R. Nora, M. Lafon, K. S. Anderson, F. J. Marshall, D. T. Michel, T. C. Sangster, W. Seka, A. A. Solodov, C. Stoeckl, B. Yaakobi, R. Betti (Laboratory for Laser Energetics, U. of Rochester); A. Casner, C. Reverdin (CEA); X. Ribeyre (CELIA); J. Peebles (U. of California, San Diego); and M. S. Wei (General Atomics). [Preview Abstract] |
Monday, October 27, 2014 3:00PM - 3:30PM |
CI1.00003: Secondary Nuclear Reactions in Magneto-Inertial Fusion Plasmas* Invited Speaker: Patrick Knapp The goal of Magneto-Inertial Fusion (MIF) is to relax the extreme pressure requirements of inertial confinement fusion by magnetizing the fuel. Understanding the level of magnetization at stagnation is critical for charting the performance of any MIF concept. We show here that the secondary nuclear reactions in magnetized deuterium plasma can be used to infer the magnetic field-radius product (BR), the critical confinement parameter for MIF [1,2]. The secondary neutron yields and spectra are examined and shown to be extremely sensitive to BR. In particular, embedded magnetic fields are shown to affect profoundly the isotropy of the secondary neutron spectra. Detailed modeling of these spectra along with the ratio of overall secondary to primary neutron yields is used to form the basis of a diagnostic technique used to infer BR at stagnation. Effects of gradients in density, temperature and magnetic field strength are examined, as well as other possible non-uniform fuel configurations. Computational results employing a fully kinetic treatment of charged reaction product transport and Monte Carlo treatment of secondary reactions are compared to results from recent experiments at Sandia National Laboratories' Z machine testing the MAGnetized Liner Inertial Fusion (MagLIF) concept [2]. The technique reveals that the charged reaction products were highly magnetized in these experiments. Implications for eventual ignition-relevant experiments with deuterium-tritium fuel are discussed.\\[4pt] *Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. \\[4pt] [1] M.M. Basko et al., Nuclear Fusion, Vol. 40, No. 1 (2000)\\[0pt] [2] S.A. Slutz et al., Phys. Plasmas 17, 056303 (2010) [Preview Abstract] |
Monday, October 27, 2014 3:30PM - 4:00PM |
CI1.00004: Fast electron transport and spatial energy deposition in imploded fast ignition cone-in-shell targets Invited Speaker: Leonard Jarrott We report on the first experimental observation and model validation of the spatial energy deposition of fast electrons into the imploded, high-density core of integrated cone-in-shell fast ignition experiments on OMEGA. Spatial energy deposition was characterized via fast electron produced K$\alpha $ fluorescence from a Cu tracer added to the CD shell. 2-D images of the Cu K$\alpha $ fluorescence were obtained using a spherically bent Bragg crystal imager. 54 of the 60 OMEGA beams (18 kJ) were used for fuel assembly, and the high intensity EP beam (10 ps, 0.5 - 1.5 kJ, I$_{\mathrm{p}}$ \textgreater 10$^{\mathrm{19}}$ W/cm$^{\mathrm{2}})$, was focused onto the inner cone tip to produce fast electrons. Cu K$\alpha $ emission from a 300 $\mu $m region surrounding the cone tip correlated well with the predicted core size from radiation-hydrodynamic simulations of the shell implosion. The emission also emanated from as far back as 100 $\mu $m from the cone tip, indicative of an electron source position with a large standoff distance from the cone tip, consistent with the presence of an extended pre-plasma from the EP pre-pulse. We observed a simultaneous increase in both K$\alpha $ yield (up to 70{\%}) and thermal neutron number (up to 2x) with increasing EP beam energy. K$\alpha $ yield data also show an improved energy coupling using the high contrast EP pulse. Comprehensive simulations of the electron production within the cone and subsequent transport into the imploded core have been performed using the implicit PIC code LSP and the hybrid-PIC code ZUMA. These simulations explain the observed K$\alpha $ shape and yield trends and identify parameters that constrain energy coupling into the compressed core. [Preview Abstract] |
Monday, October 27, 2014 4:00PM - 4:30PM |
CI1.00005: Demonstration of thermonuclear conditions in Magnetized Liner Inertial Fusion experiments Invited Speaker: Matthew Gomez The Magnetized Liner Inertial Fusion concept [S. A. Slutz et al., Phys. Plasmas 17, 056303 (2010)] utilizes a magnetic field and laser heating to relax the implosion requirements to achieve inertial confinement fusion. The first experiments to test the concept were recently conducted utilizing the 19 MA, 100 ns Z machine, the 2.5 kJ, 1 TW Z Beamlet laser, and the 10 T Applied B-field on Z coils. Despite the relatively slow implosion velocity (70 km/s) in these experiments, electron and ion temperatures at stagnation were approximately 3 keV, and thermonuclear DD neutron yields up to 2e12 have been produced. X-ray emission from the fuel at stagnation had a width ranging from 60-120 microns over a roughly 6 mm height and lasted approximately 2 ns. X-ray spectra from these experiments are consistent with a stagnation density of the hot fuel equal to 0.4 g/cm3. In these experiments 1-5e10 secondary DT neutrons were produced. Given that the areal density of the plasma was approximately 2 mg/cm$^{2}$, this indicates the stagnation plasma was significantly magnetized. This is consistent with the anisotropy observed in the DT neutron time of flight spectra. Control experiments where the laser and/or magnetic field were not utilized failed to produce stagnation temperatures greater than 1 keV and DD yields greater than 1e10. An additional control experiment where the fuel contained a sufficient dopant fraction to radiate away the laser energy deposited in the fuel also failed to produce a relevant stagnation temperature. The results of these experiments are consistent with a thermonuclear neutron source.\\[4pt] *Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under Contract No. DE-AC04-94AL85000. [Preview Abstract] |
Monday, October 27, 2014 4:30PM - 5:00PM |
CI1.00006: Diagnosing Magnetized Liner Inertial Fusion experiments on Z Invited Speaker: Stephanie Hansen Recent Magnetized Liner Inertial Fusion (MagLIF) experiments performed at Sandia's Z facility have demonstrated DD fusion neutron yields above 10$^{\mathrm{12}}$ and effective confinement of charged fusion products by the flux-compressed magnetic field signaled by \textgreater 10$^{\mathrm{10}}$ secondary DT neutrons. The neutron diagnostics are complemented by an extensive suite of visible and x-ray diagnostics providing power, imaging, and spectroscopic data. This talk will present analyses of emission and absorption features from the imploding and stagnating plasma that provide a consistent picture of the magnetic drive and the temperatures, densities, mix, and gradients in the fuel and liner at stagnation. [Preview Abstract] |
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