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 JI2: ICF Compression, Equations of State and Z-pinches |
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Chair: Tom Mehlhorn, Sandia National Laboratories Room: Centennial I |
Tuesday, November 3, 2009 2:00PM - 2:30PM |
JI2.00001: Hugoniot Measurements of Diamond and $\alpha$-Quartz in the TPa Regime: Implications for Astrophysics, ICF, and HED Physics Invited Speaker: The development of an ultra-high velocity ($>$ 40 km/s) flyer plate capability at the Sandia Z Machine has enabled TPa shock wave experiments with unprecedented accuracy. Here we present the results of Hugoniot measurements on diamond and z-cut, $\alpha$-quartz in the 0.5-1.5 and 0.1-1.6 TPa regime, respectively. The diamond measurements are inclusive of a large solid-liquid coexistence region, and together with quantum molecular dynamics (QMD) calculations, provide compelling evidence for the existence of a diamond-bc8-liquid triple point along the Hugoniot. The new quartz Hugoniot data reveal significant errors in the current, widely-used quartz standard and have immediate ramification for the equations of state of deuterium, helium, and diamond at pressures relevant to giant planets and other high energy density conditions. This work provides a foundation for the use of quartz as an extremely accurate standard for use in multi-Mbar shock wave experiments, as well as a benchmark for first-principles calculations of high-pressure material response where processes such as disorder, dissociation, and ionization are significant. [Preview Abstract] |
Tuesday, November 3, 2009 2:30PM - 3:00PM |
JI2.00002: High-Precision Measurements of the Equation of State of Polymers at 100 to 1000 GPa Using Laser-Driven Shock Waves Invited Speaker: The equation of state (EOS) of materials at extreme temperatures and pressures is of interest to astrophysics, high-energy-density physics, and inertial confinement fusion (ICF). The high-pressure ($>$100 GPa) behavior of polymer materials is essential to the understanding of ablator materials for ignition targets. EOS measurements on CH$_{x}$ provide benchmarks on the behavior of polymers under extreme conditions and the effect of stoichiometry (i.e., the C:H ratio) on that behavior. High-power lasers produce shock pressures greater than 100 GPa, and recent advances in diagnostics and analysis have made it possible to perform highly accurate measurements of shock velocity. This improves upon the impedance-matching technique for laser-driven shock experiments, producing $\sim $1{\%} precision at extreme pressures. The OMEGA laser is used to produce principal (single-shock) Hugoniot EOS measurements on polystyrene (CH), polypropylene (CH$_{2})$, GDP (C$_{43}$H$_{56}$O), and Ge-doped GDP at shock pressures of $\sim $100 to 1000 GPa. We also present a novel target design that provides double-shock (re-shock) data together with the above data. These data are pertinent to ICF target designs that use multiple shocks to approximate an isentropic compression. Results of the single- and double-shock experiments on these polymers are presented and compared to various EOS models. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC52-08NA28302. In collaboration with T.R. Boehly, D.E. Fratanduono, D.D. Meyerhofer (LLE), D.G. Hicks, P.M. Celliers, and G.W. Collins (LLNL). [Preview Abstract] |
Tuesday, November 3, 2009 3:00PM - 3:30PM |
JI2.00003: X-ray Radiography and Scattering Diagnosis of Dense Shock-Compressed Matter Invited Speaker: Spectrally resolved x-ray Thomson scattering is an established technique that allows characterizing Fermi degenerate dense plasmas accessible in laser shocked-compressed foil experiments. It has been used in a variety of experiments that, besides measuring plasma density and temperature, served as critical test for models that calculate important plasma parameters like structure factors, bound-free contributions, and ionization energy lowering in warm dense matter. Experiments realized at the TITAN facility at Lawrence Livermore National Laboratory apply ultra-short pulse laser produced K- x rays to characterize plasmas at pressures above 1.5 Mbar that are produced with an energetic nanosecond laser. High energy x-rays produced by the short pulse laser allow probing compressed matter with a high temporal resolution (about 10 ps). From collective and non-collective scattering spectra mass density of the compressed Boron is inferred. X-ray radiography has been used as an independent way to characterize the mass density of matter for identical drive conditions. Here, we use K- X rays in a point projection scheme to probe the shock wave. Densities ranging from 3 to 4 g/cc have been measured, in excellent agreement with the x-ray Thomson scattering data. These radiography data combined with accurate measurement of the Plasmon dispersion in shocked Boron help improving the accuracy of the collision model as well as structure factor calculation. [Preview Abstract] |
Tuesday, November 3, 2009 3:30PM - 4:00PM |
JI2.00004: Validated, 3-dimensional, magneto-hydrodynamic simulations of optimized single and nested wire array z-pinches with detailed circuit coupling Invited Speaker: Wire array Z-pinches have been used successfully for many years as a powerful x-ray source, as a dynamic hohlraum, and as an intense K-shell source. Significant progress has been made in modeling these 3D resistive plasmas however predictive modeling also requires an accurate representation of the power delivered to the load, which is an uncertainty potentially as large as the MHD implosion dynamics. We present 3D resistive MHD simulations of wire arrays that are coupled to a transmission line equivalent of the Z generator separately representing the 4 vacuum insulated transmission lines that join through a double post-hole convolute into a final feed to the array. Significant (multi-MA) current losses are shown to occur in the convolute and the final feed. This limits the array performance and must be correctly accounted for to accurately represent the generator response. Our simulations are validated against data for compact, 20mm diameter, 10mm long wire arrays. This is the most comprehensive experimental data set for single and nested wire arrays and includes voltage, current, x-ray power and energy, and multiple mass distribution measurements. These data tightly constrain our simulation results and allow us to describe, for the first time, the detailed mechanism by which nested arrays can be used to narrow the radial mass distribution and increase the peak x-ray power. We use these results to define criteria for optimizing the x-ray power output from these and other nested wire array sources. In collaboration with: M. E. Cuneo, J.P.Chittenden, W.A. Stygar, B. Jones, D. J. Ampleford, E.M. Waisman, M.E. Savage, K. LeChien, D.B. Sinars [Preview Abstract] |
Tuesday, November 3, 2009 4:00PM - 4:30PM |
JI2.00005: Acceleration to High Velocities and Heating by Impact Using Nike KrF laser Invited Speaker: Shock ignition, impact ignition, as well as higher intensity conventional hot spot ignition designs reduce driver energy requirement by pushing the envelope in laser intensity and target implosion velocities. This talk will describe experiments that for the first time reach target velocities in the range of 700 -- 1000 km/s. The highly accelerated planar foils of deuterated polystyrene, some with bromine doping, are made to collide with a witness foil to produce extreme shock pressures and result in heating of matter to thermonuclear temperatures. Target acceleration and collision are diagnosed using large field of view monochromatic x-ray imaging with backlighting as well as bremsstrahlung self-emission. The impact conditions are diagnosed using DD fusion neutron yield, with over $10^6$ neutrons produced during the collision. Time-of-flight neutron detectors are used to measure the ion temperature upon impact, which reaches 2 -- 3 keV. The experiments are performed on the Nike facility, reconfigured specifically for high intensity operation. The short wavelength and high illumination uniformity of Nike KrF laser uniquely enable access to this new parameter regime. Intensities of $(0.4 -- 1.2)$ x $10^{15}$ W/cm$^2$ and pulse durations of $0.4 -- 2$ ns were utilized. Modeling of the target acceleration, collision, and neutron production is performed using the FAST3D radiation hydrodynamics code with a non-LTE radiation model. Work is supported by US Department of Energy. [Preview Abstract] |
Tuesday, November 3, 2009 4:30PM - 5:00PM |
JI2.00006: Magnetized Liner Inertial Fusion Invited Speaker: The natural geometry for magnetically driven implosions is cylindrical, but cylindrical implosions require more radial convergence than spherical implosions due to reduced volume convergence. Fuel magnetization and preheat can ameliorate this problem by reducing conduction losses and the required compressive heating. Assuming a deuterium-tritium fuel preheated to 200-500 eV and magnetized with a 10T field, numerical simulations indicate that fusion conditions could be obtained by cylindrical liner implosions driven by the Z accelerator. According to the simulations the initial axial magnetic field is compressed to more than 100 MG, which inhibits thermal conduction and the escape of alpha particles. The inhibited thermal transport allows the fuel to reach temperatures exceeding 5 keV despite an implosion velocity of only 10 cm/$\mu $s. The final fuel density is about 1 g/cc, which is high enough to axially trap alpha particles for cylinders less than 1 cm long with a purely axial magnetic field. Analytic and numeric calculations indicate that the fuel can be heated to 200-500 eV with 3-10 kJ of green laser light, which could be provided by the Z-Beamlet laser. The Magneto-Rayleigh-Taylor instability poses the greatest threat to this approach to fusion. 2D numerical simulations indicate that the liner walls must have a substantial initial thickness (15-30{\%} of the radius) to maintain integrity throughout the implosion. Z and Z Beamlet experiments are underway to test the various components of this concept. [Preview Abstract] |
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