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Ideal and non-ideal MHD regimes of wire array implosion obtained in 3D hybrid simulations and observed during experiments at NTF

Mehlhorn, Thomas A.; Coverdale, Christine A.; Jones, Brent M.; Deeney, Christopher D.

Recent 3D hybrid simulation of a plasma current-carrying column revealed two regimes of sausage and kink instability development. In the first regime, with small Hall parameter, development of instabilities leads to appearance of large-scale axial perturbations and eventually to the bending of the plasma column. In the second regime, with five times larger Hall parameter, small-scale perturbations dominated and no bending of the plasma column was observed. Simulation results are compared to recent experimental data, including laser probing, x-ray spectroscopy and time-gated x-ray imaging during wire array implosions at NTF.

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TYPE Conference YEAR 2004
OSTI

Increasing Z-pinch vacuum hohlraum capsule coupling efficiency

Vesey, Roger A.; Cuneo, Michael E.; Bennett, Guy R.; Mehlhorn, Thomas A.

Symmetric capsule implosions in the double-ended vacuum hohlraum (DEH) on Z have demonstrated convergence ratios of 14-21 for 2.15-mm plastic ablator capsules absorbing 5-7 kJ of x-rays, based on backlit images of the compressed ablator remaining at peak convergence [1]. Experiments with DD-filled 3.3-mm diameter capsules designed to absorb 14 kJ of x-rays have begun as an integrated test of drive temperature and symmetry, complementary to thin-shell symmetry diagnostic capsules. These capsule implosions are characterized by excellent control of symmetry (< 3% time-integrated), but low hohlraum efficiency (< 2%). Possible methods to increase the capsule absorbed energy in the DEH include mixed-component hohlraums, large diameter foam ablator capsules, transmissive shine shields between the z-pinch and capsule, higher spoke electrode x-ray transmission, a double-sided power feed, and smaller initial radius z-pinch wire arrays. Simulations will explore the potential for each of these modifications to increase the capsule coupling efficiency for near-term experiments on Z and ZR.

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TYPE Conference YEAR 2004
OSTI

Mapping the backbone of science

Proposed for publication in Scientometrics.

Boyack, Kevin W.

This paper presents a new map representing the structure of all of science, based on journal articles, including both the natural and social sciences. Similar to cartographic maps of our world, the map of science provides a bird's eye view of today's scientific landscape. It can be used to visually identify major areas of science, their size, similarity, and interconnectedness. In order to be useful, the map needs to be accurate on a local and on a global scale. While our recent work has focused on the former aspect, this paper summarizes results on how to achieve structural accuracy. Eight alternative measures of journal similarity were applied to a data set of 7,121 journals covering over 1 million documents in the combined Science Citation and Social Science Citation Indexes. For each journal similarity measure we generated two-dimensional spatial layouts using the force-directed graph layout tool, VxOrd. Next, mutual information values were calculated for each graph at different clustering levels to give a measure of structural accuracy for each map. The best co-citation and inter-citation maps according to local and structural accuracy were selected and are presented and characterized. These two maps are compared to establish robustness. The inter-citation map is then used to examine linkages between disciplines. Biochemistry appears as the most interdisciplinary discipline in science.

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TYPE Journal Article YEAR 2004
OSTI

Pulsed-power-driven high energy density physics and inertial confinement fusion research

Matzen, M.K.

The Z accelerator [R.B. Spielman, W.A. Stygar, J.F. Seamen et al., Proceedings of the 11th International Pulsed Power Conference, Baltimore, MD, 1997, edited by G. Cooperstein and I. Vitkovitsky (IEEE, Piscataway, NJ, 1997), Vol. 1, p. 709] at Sandia National Laboratories delivers {approx}20 MA load currents to create high magnetic fields (>1000 T) and high pressures (megabar to gigabar). In a z-pinch configuration, the magnetic pressure (the Lorentz force) supersonically implodes a plasma created from a cylindrical wire array, which at stagnation typically generates a plasma with energy densities of about 10 MJ/cm{sup 3} and temperatures >1 keV at 0.1% of solid density. These plasmas produce x-ray energies approaching 2 MJ at powers >200 TW for inertial confinement fusion (ICF) and high energy density physics (HEDP) experiments. In an alternative configuration, the large magnetic pressure directly drives isentropic compression experiments to pressures >3 Mbar and accelerates flyer plates to >30 km/s for equation of state (EOS) experiments at pressures up to 10 Mbar in aluminum. Development of multidimensional radiation-magnetohydrodynamic codes, coupled with more accurate material models (e.g., quantum molecular dynamics calculations with density functional theory), has produced synergy between validating the simulations and guiding the experiments. Z is now routinely used to drive ICF capsule implosions (focusing on implosion symmetry and neutron production) and to perform HEDP experiments (including radiation-driven hydrodynamic jets, EOS, phase transitions, strength of materials, and detailed behavior of z-pinch wire-array initiation and implosion). This research is performed in collaboration with many other groups from around the world. A five year project to enhance the capability and precision of Z, to be completed in 2007, will result in x-ray energies of nearly 3 MJ at x-ray powers >300 TW.

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TYPE Conference YEAR 2004
OSTI

Self-assembled, ordered gold nanocrystal/silica thin films for prism-based surface plasmon resonance sensors

Fan, Hongyou; Brinker, C.J.

Gold nanocrystal(NC)/silica films are synthesized through self-assembly of water-soluble gold nanocrystal micelles and silica by sol-gel processing. Absorption and transmission spectra show a strong surface plasmon resonance absorption peak at {approx}520 nm. Angular excitation spectra of surface plasmon show a steep dip in the reflectivity curve at {approx}65{sup o} depending on the thickness and refractive index of the gold NC/silica film. A potential SPR sensor with enhanced sensitivities can be realized based on these gold NC/silica films.

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TYPE Conference YEAR 2004
OSTI
Results 89251–89300 of 100,993
Results 89251–89300 of 100,993
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