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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 2609-2612 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: It is shown that laser driven hohlraums obtain significant internal pressures which affect the hydrodynamics of high-energy density shock-tube experiments. By incorporating this previously neglected hohlraum pressure effect (in addition to the usual x-ray drive) into computer simulations which model the NOVA laser driven supernova remnant experiment [R. P. Drake, S. G. Glendinning, K. Estabrook, B. A. Remington, R. McCray, R. J. Williams, L. J. Suter, T. B. Smith, J. J. Carroll III, R. A. London, and E. Liang, Phys. Rev. Lett. 81, 2068 (1998)], calculations are able to reproduce the observed structure of hydrodynamic features. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: More than a decade after the explosion of supernova 1987A, unresolved discrepancies still remain in attempts to numerically simulate the mixing processes initiated by the passage of a very strong shock through the layered structure of the progenitor star. Numerically computed velocities of the radioactive 56Ni and 56Co, produced by shock-induced explosive burning within the silicon layer, for example, are still more than 50% too low as compared with the measured velocities. To resolve such discrepancies between observation and simulation, an experimental testbed has been designed on the Omega Laser for the study of hydrodynamic issues of importance to supernovae (SNe). In this paper, results are presented from a series of scaled laboratory experiments designed to isolate and explore several issues in the hydrodynamics of supernova explosions. The results of the experiments are compared with numerical simulations and are generally found to be in reasonable agreement. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 2197-2202 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Starting from the fundamental ion and electron fluid equations, a "master" equilibrium equation set is constructed for axisymmetric toroidal plasmas. These equations retain the effects of different ion and electron densities, temperatures, sheared rotation, and electric forces. The master equation is then examined in various limits including the non-neutral plasma limit. An ordering is assumed which makes the effects of the Reynolds stress, pressure, magnetic stress, and electric field stress all comparable emphasizing the natural transition from the non-neutral case to the quasi-neutral one. For sub-relativistic flows, charge separation effects are only significant for nearly force-free plasmas. A set of equilibrium equations are derived for three different cases: (A) ni(approximate)ne, (B) ni≠ne≠0, and (C) ni=0 and ne≠0. In the pure electron plasma case, the resulting equilibrium equation includes the effects of toroidal rotation, poloidal magnetic field, and electron pressure extending the equation of Daugherty and Levy [Phys. Fluids 10, 155 (1967)]. © 1998 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 4 (1997), S. 3565-3580 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The sudden release of magnetic free energy, as occurs in spectacular solar flare events, tokamak disruptions, and enigmatic magnetospheric substorms, has long defied any acceptable theoretical explanation. Usual attempts at explaining these explosive events invoke magnetic reconnection and/or ideal magnetohydrodynamic (MHD) instability. However, neither of these two mechanisms can explain the fast time scales without nonlinear destabilization. Recently, Cowley et al. [Phys. Plasmas 3, 1848 (1996)] have demonstrated a new mechanism for nonlinear explosive MHD destabilization of a line tied Rayleigh–Taylor model. In this paper, this picture is generalized to arbitrary magnetic field geometries. As an intermediate step, the ballooning equation in a general equilibrium is derived including the effects of magnetic field curvature, shear, and gravity. This equation determines the linear stability of the plasma configuration and the behavior of the plasma displacement along the magnetic field line. The nonlinear equation which determines the time and spatial dependence, transverse to the equilibrium magnetic field, of the plasma displacement is obtained in fifth order of the expansion. The equations show that explosive behavior is a natural and generic property of ballooning instabilities close to the linear stability boundary. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 2472-2474 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The magnetotail-like equilibrium model of Lembège and Pellat [Phys. Fluids, 25, 1995 (1982)] has been used in a number of stability calculations over the past 13 years. Most of these computations examine collisionless tearing—a mode of tail instability first suggested by Coppi et al. [Phys. Rev. Lett. 16, 1207 (1966)]—or other kinetic modes and involve both analytical and computer analysis. In this Communication it is shown, analytically, that the equilibrium model of Lembège and Pellat is unstable according to ideal magnetohydrodynamics (MHD). More precisely, for the ideal MHD stability theory of Bernstein et al. [Proc. R. Soc. London Ser. A 244, 17 (1958)] it is proven that Λ=p′+Γp (v″/v′)〈0. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 1976-1981 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The problem of plasma flow relative to a modulated magnetic field has been the subject of several studies. One motivation for studying this problem is the possibility of using a deliberately imposed surface of magnetic islands as a means of velocity profile control. This subject is also of importance for the study of stability against ideal and resistive magnetohydrodynamic (MHD) modes and the topic of locked modes. A two-dimensional (2-D) MHD simulation code is used to examine the behavior of a plasma flowing, in steady state, past a modulated magnetic field in "slab geometry.'' It is shown that at "low'' velocities the stress is dominated by the Maxwell and the viscosity terms and that forces are exchanged between the plasma and the magnetic field in a narrow boundary surrounding the island. It is found that the island is suppressed when the viscous force at the separatrix exceeds the maximum force that can be supported by an island. For "high'' velocities (velocities beyond the critical velocity for island suppression), the stress is dominated by the Maxwell and the Reynolds terms, and the exchange of forces is taking place in a narrow region around the point where the plasma flow velocity matches the Alfvén speed. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 3502-3504 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Multipole stability with respect to quasielectrostatic low frequency modes (frequencies smaller than the average ion bounce frequency) is revisited. Aside from localized modes found previously by M. N. Rosenbluth [Phys. Fluids 11, 869 (1968)], it is shown that convective type modes that are equipotentials along field lines are likely to be more unstable, when the average curvature drift is positive (v‘〈0) and smaller than the local curvature drift.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 1259-1264 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The spectrum of unstable perturbations of a simple magnetized atmosphere is studied. Magnetic field lines are straight, horizontal, and line tied to conducting walls at both ends. The temperature has horizontal variation across the field lines as well as vertical variation. The unstable spectrum close to marginal stability is found to be continuous from zero to a maximum growth rate. The structure of the unstable continuum modes is calculated in the dissipationless limit. The presence of singularities in the eigenfunction does not affect the growth rate significantly, nor does it lead to plasma heating. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 4043-4051 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Theoretically, high-β (β∼1) tokamaks offer a large fusion power efficiency advantage over low-β devices. However, if high-β tokamaks are inherently unstable then such devices will never be realized. In particular, kink modes are thought to be the most serious obstacle to high-β operations. High-β tokamaks are characterized by a very large Shafranov shift with a thin "boundary layer" on the outboard side of the device and a large "core" region of vertical flux surfaces comprising most of the central volume. In this paper, the energy principle is used to compute the magnetohydrodynamic internal kink stability of such devices in the large aspect ratio limit with a low toroidal mode number. A class of internal kink mode similar to the usual low-β kink is present; the stability against these modes is computed. A set of parameters describing a kink stable high-β equilibrium is given. Stability is shown to be dependent on the shape of the plasma boundary. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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