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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 4156-4162 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Laser-based experiments have shown that Rayleigh–Taylor (RT) growth in thin, perturbed copper foils leads to a phase dominated by narrow spikes between thin bubbles. These experiments were well modeled and diagnosed until this " spike" phase, but not into this spike phase. Experiments were designed, modeled, and performed on the OMEGA laser [T. R. Boehly, D. L. Brown, R. S. Craxton et al., Opt. Commun. 133, 495 (1997)] to study the late-time spike phase. To simulate the conditions and evolution of late time RT, a copper target was fabricated consisting of a series of thin ridges (spikes in cross section) 150 μm apart on a thin flat copper backing. The target was placed on the side of a scale-1.2 hohlraum with the ridges pointing into the hohlraum, which was heated to 190 eV. Side-on radiography imaged the evolution of the ridges and flat copper backing into the typical RT bubble and spike structure including the " mushroom-like feet" on the tips of the spikes. RAGE computer models [R. M. Baltrusaitis, M. L. Gittings, R. P. Weaver, R. F. Benjamin, and J. M. Budzinski, Phys. Fluids 8, 2471 (1996)] show the formation of the " mushrooms," as well as how the backing material converges to lengthen the spike. The computer predictions of evolving spike and bubble lengths match measurements fairly well for the thicker backing targets but not for the thinner backings. © 2001 American Institute of Physics.
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  • 2
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Rayleigh–Taylor instability of radiatively driven thin copper foils is studied under pure ablation, as well as with beryllium buffers to provide additional pressure drive, in support of the target design for Inertial Confinement Fusion. Modeling was done with the RAGE adaptive mesh refinement code [R. M. Baltrusaitis, M. L. Gittings, R. P. Weaver, R. F. Benjamin, and J. M. Budzinski, Phys. Fluids 8, 2471 (1996)] of experiments done on the OMEGA [T. R. Boehly, D. L. Brown, R. S. Craxton et al., Opt. Commun. 133, 495 (1997)] laser. The copper foils were typically 11.5 μm thick with 0.45 μm amplitude and 45 μm wavelength cosine surface perturbations. The beryllium layer was 5 μm thick. The drive was a "PS26"-like [J. D. Lindl, Phys. Plasmas 2, 3933 (1995)] laser pulse delivering peak 160–185 eV radiation temperatures. Good agreement between experiment and simulation has been obtained out to 4.5 ns. Mechanisms for late time agreement are discussed. © 2001 American Institute of Physics.
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3006-3011 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In an experiment relevant to the fast ignitor fusion concept, a preformed plasma simulating the corona of a fusion target has been probed with laser intensities exceeding 1018 W/cm2. It is seen that the f number of the probe beam is increased as it propagates through the target plasma—a channeling of the power. The transmission and backscatter of the probe beam have been examined, and the analysis suggests anomalous absorption of laser light in shorter scale length plasmas. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 4005-4008 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A preformed plasma simulating the corona of a fast ignitor target has been probed with 527 nm and 1054 nm lasers exceeding the critical power for ponderomotive electron cavitation. For both colors, the f number of the probe beam is increased as it propagates through the plasma. Transmission of the diffraction-limited beams is higher for the green than for the 1 μm case. © 1998 American Institute of Physics.
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 211-221 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Recent experiments have shown that low density foam layers can significantly mitigate the perturbing effects of beam nonuniformities affecting the acceleration of thin shells. This problem is studied parametrically with two-dimensional LASNEX [G. B. Zimmerman and W. L. Kruer, Comments Plasma Phys. Controlled Fusion 2, 51 (1975)]. Foam-buffered targets are employed, consisting typically of 250 Å of gold, and 50 μm of 50 mg/cm3 C10H8O4 foam attached to a 10 μm foil. In simulation these were characteristically exposed to 1.2 ns, flat-topped green light pulses at 1.4×1014 W/cm2 intensity, bearing 30 μm lateral perturbations of up to 60% variation in intensity. Without the buffer layers the foils were severely disrupted by 1 ns. With buffering only minimal distortion was manifest at 3 ns. The smoothing is shown to derive principally from the high thermal conductivity of the heated foam. The simulation results imply that (1) the foam thickness should exceed the disturbance wavelength; (2) intensities exceeding 5×1013 W/cm2 are needed for assured stability beyond 2 ns; (3) longer foams at lower densities are needed for effective mitigation with shorter wavelength light; (4) the gold layer hastens conversion of the structured foam to a uniform plasma. © 1998 American Institute of Physics.
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1379-1384 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Creation of a low density, high temperature plasma buffer between the absorption and ablation layers of a directly driven inertial confinement fusion implosion capsule has been proposed as a means to reduce "early time" imprint from laser nonuniformities. This thermal smoothing blanket might be created from a low density foam layer wrapped around the deuterium–tritium filled microballoon. Preliminary spherical implosion tests of this concept using a polystyrene foam layer surrounding a glass microballoon were performed at the Nova laser [Rev. Sci. Instrum. 57, 2101 (1986)], using a 527 nm drive wavelength. Comparison of capsule yield and imploded core symmetry showed promising improvements in overall target performance, relative to one-dimensional undegraded hydrodynamic simulations, when the foam-buffer layer was present. © 1997 American Institute of Physics.
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 481-484 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Linear waves in a magnetized cold electron plasma are studied as a means of further understanding the mechanism of field penetration in such devices as plasma opening switches. The one-dimensional wave penetration into a nonuniform plasma, discovered by others in earlier work, has been extended to two dimensions by the linear analysis. An exact solution is presented for waves propagating along a density discontinuity.
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 4 (1992), S. 294-297 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The velocity advection, me(ve⋅∇)ve, terms in the momentum equation for electrons in a collisionless plasma are shown to introduce an effective resistivity on the currents drawn from a bounding cathode. This leads to nonlinear diffusive penetration of an externally driven magnetic field, which at time t and height y above the cathode, penetrates to a depth δ obeying the scaling δ∼(t/y)1/3.
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 2307-2314 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In collisionless simulations of the plasma erosion opening switch, a highly conductive plasma allows magnetic field penetration through the entire length of the plasma, to depths almost two orders of magnitude greater than the collisionless skin depth, c/ωpe. Field penetration is accomplished by a narrow (skin-depth-like) current channel that migrates through the plasma. The plasma behind the current channel is unable to shield the rising magnetic field from the body of the plasma and allows it to penetrate almost instantly and completely through the plasma up to the current channel. The migration of the channel and the penetration of the field appear to occur in the absence of both Coulomb collisions and instabilities. These unusual features are permitted by the electric field structure in the plasma behind the current channel and the presence of conducting boundaries that can emit electrons.
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 1115-1127 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The nonlinear transport of magnetic field in collisionless plasmas, as present in the plasma opening switch (POS), using the implicit multifluid simulation code anthem [J. Comput. Phys. 71, 429 (1987)] is studied. The focus is on early time behavior in the electron–magnetohydrodynamic (EMHD) limit, with the ions fixed, and the electrons streaming as a fluid under the influence of ve×B Hall forces. Through simulation, magnetic penetration and magnetic exclusion waves are characterized, due to the Hall effect in the presence of transverse density gradients, and the interaction of these Hall waves with nonlinear diffusive disturbances from electron velocity advection, (ve⋅∇)ve, is studied. It is shown how these mechanisms give rise to the anode magnetic insulation layer, central diffusion, and cathode potential hill structures seen in earlier opening switch plasmas studies.
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