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  • 1
    Electronic Resource
    Electronic Resource
    Thomson scattering from laser plasmas : The 40th annual meeting of the division of plasma physics of the american physical society (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 2117-2128 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thomson scattering has recently been introduced as a fundamental diagnostic of plasma conditions and basic physical processes in dense, inertial confinement fusion plasmas. Experiments at the Nova laser facility [E. M. Campbell et al., Laser Part. Beams 9, 209 (1991)] have demonstrated accurate temporally and spatially resolved characterization of densities, electron temperatures, and average ionization levels by simultaneously observing Thomson scattered light from ion acoustic and electron plasma (Langmuir) fluctuations. In addition, observations of fast and slow ion acoustic waves in two-ion species plasmas have also allowed an independent measurement of the ion temperature. These results have motivated the application of Thomson scattering in closed-geometry inertial confinement fusion hohlraums to benchmark integrated radiation-hydrodynamic modeling of fusion plasmas. For this purpose a high energy 4ω probe laser was implemented recently allowing ultraviolet Thomson scattering at various locations in high-density gas-filled hohlraum plasmas. In particular, the observation of steep electron temperature gradients indicates that electron thermal transport is inhibited in these gas-filled hohlraums. Hydrodynamic calculations which include an exact treatment of large-scale magnetic fields are in agreement with these findings. Moreover, the Thomson scattering data clearly indicate axial stagnation in these hohlraums by showing a fast rise of the ion temperature. Its timing is in good agreement with calculations indicating that the stagnating plasma will not deteriorate the implosion of the fusion capsules in ignition experiments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873499
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  • 2
    Electronic Resource
    Electronic Resource
    Laser beam propagation and channel formation in underdense plasmas (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 2825-2834 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Experimental results are presented which show the formation of density channels in a preformed plasma by a 100 ps laser beam focused with different f/number lenses. The density channels are diagnosed by an interferometer. The experiments are made with both line foci and circular foci up to intensities of 5×1016 W/cm2. The experimental channel size and density perturbation compare favorably with the predictions of two-dimensional theoretical models. The limited axial extent of the channels is shown to be due to the onset of the filamentation instability. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871180
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  • 3
    Electronic Resource
    Electronic Resource
    Diffusive, supersonic x-ray transport in radiatively heated foam cylinders (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 2126-2134 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Diffusive supersonic radiation transport, where the ratio of the diffusive radiation front velocity to the material sound speed 〉2 has been studied in experiments on low density (40 mg/cc to 50 mg/cc) foams. Laser-heated Au hohlraums provided a radiation drive that heated SiO2 and Ta2O5 aerogel foams of varying lengths. Face-on emission measurements at 550 eV provided clean signatures of the radiation breakout. The high quality data provides new detailed information on the importance of both the fill and wall material opacities and heat capacities in determining the radiation front speed and curvature. The Marshak radiation wave transport is studied in a geometry that allows direct comparisons with analytic models and two-dimensional code simulations. Experiments show important effects that will affect even nondiffusive and transonic radiation transport experiments studied by others in the field. This work is of basic science interest with applications to inertial confinement fusion and astrophysics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.874057
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  • 4
    Electronic Resource
    Electronic Resource
    Linear stability of an accelerated, current carrying wire array (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 3302-3315 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The linear stability of an array of a large number of thin wires is considered. The wires form a cylindrical surface, accelerated toward the axis under the action of a current. Stability equations are derived and a complete classification of the modes is presented. In agreement with Felber and Rostoker [Phys. Fluids 24, 1049 (1981)], it is shown that there exist two types of modes: medial modes, with deformation in the rz plane, and lateral modes, with only azimuthal deformation. For a given axial wave number, k, the most unstable medial mode has all the wires moving in phase similar to an axisymmetric mode for a continuous shell, whereas the most unstable lateral perturbation has opposite displacements of neighboring wires. Lateral modes are of particular interest because they may remain unstable for parameters where medial modes are stable. Numerical analysis of the dispersion relation for a broad range of modes is presented. Some limiting cases are discussed. It is shown that k1/2 scaling holds until surprisingly high wave numbers, even exceeding the inverse interwire distance. In the long-wavelength limit, the wires behave as a continuous shell with strong anisotropy of the electrical conductivity, i.e., high along the wires and vanishing across the wires. The results differ considerably from the modes of a thin, perfectly conducting shell. In particular, a new "zonal flow" mode is identified.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873598
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  • 5
    Electronic Resource
    Electronic Resource
    Magnetohydrodynamic solution for a Z pinch showing the production of a hot spot (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 1737-1740 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Two-dimensional LASNEX [National Technical Information Service Document No. DE 81026329 (Zimmerman, Report No. UCRL-74811, 1973)] calculations are made for a Z pinch on Saturn, the low-impedance, low-inductance electron accelerator at the Sandia National Laboratories [D. D. Bloomquist et al. Proceedings of the Sixth IEEE Pulsed Power Conference, Arlington, VA, edited by P. J. Turchi and B. H. Bernstein (Institute of Electronics and Electrical Engineers, New York, 1987), p. 310]. The experiment is characterized by a current of 6 MA with a tungsten wire load (4 mg) at 2 mm. Two-dimensional calculations show the evolution of the Rayleigh–Taylor instability to the bubble and spike phase, causing high-density islands to form in the pinch opposite the bubbles. The two-dimensional energy flow causes a "hot spot'' to evolve, which is shown to agree in its size and brightness with pinhole camera measurements. This is the first explicit calculation of a hot spot in two dimensions employing the full magnetohydrodynamic equations. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871691
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