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  • 1
    Electronic Resource
    Electronic Resource
    Magnetohydrodynamic scaling: From astrophysics to the laboratory : The 42nd annual meeting of the division of plasma physics of the American Physical Society and the 10th international congress on plasma physics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 1804-1816 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: During the last few years, considerable progress has been made in simulating astrophysical phenomena in laboratory experiments with high-power lasers. Astrophysical phenomena that have drawn particular interest include supernovae explosions; young supernova remnants; galactic jets; the formation of fine structures in late supernovae remnants by instabilities; and the ablation-driven evolution of molecular clouds. A question may arise as to what extent the laser experiments, which deal with targets of a spatial scale of ∼100 μm and occur at a time scale of a few nanoseconds, can reproduce phenomena occurring at spatial scales of a million or more kilometers and time scales from hours to many years. Quite remarkably, in a number of cases there exists a broad hydrodynamic similarity (sometimes called the "Euler similarity") that allows a direct scaling of laboratory results to astrophysical phenomena. A discussion is presented of the details of the Euler similarity related to the presence of shocks and to a special case of a strong drive. Constraints stemming from the possible development of small-scale turbulence are analyzed. The case of a gas with a spatially varying polytropic index is discussed. A possibility of scaled simulations of ablation front dynamics is one more topic covered in this paper. It is shown that, with some additional constraints, a simple similarity exists. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1344562
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  • 2
    Electronic Resource
    Electronic Resource
    Particle trajectories in a sheath in a strongly tilted magnetic field (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 808-817 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this paper we provide a systematic analysis of particle motion in a sheath under the condition that the magnetic field intersects the wall at a small angle. A general qualitative classification of particle trajectories is presented. It is shown that the ion motion in the ion subsheath can be described in terms of an adiabatic invariant, despite the fact that the electrostatic potential varies on a scale comparable with the ion gyroradius. Trajectories of heavy impurity ions for the cases of both low and high ionization states have been found. Electron motion is considered, and it is shown that, if the electron gyroradius is much less than the electron Debye radius, electrons hit the wall at shallow angles. The possible role of an electrostatic field directed along the wall is briefly discussed. The results obtained in the paper can be used for evaluating the sputtering rate and the secondary emission coefficient, as well as for analyzing sheath stability and for formulating the boundary conditions for the bulk of the plasma. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872764
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  • 3
    Electronic Resource
    Electronic Resource
    Destabilizing effect of thermal conductivity on the Rayleigh–Taylor instability in a plasma (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 4797-4800 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: It is shown that the Rayleigh–Taylor instability in a compressible medium is not necessarily stabilized by thermal conductivity. It is pointed out that one can use the destabilization effect for in situ measurements of thermal conductivity in high-energy-density experiments. The other consequence is generation of small-scale turbulence in supernovae, giving rise to significant turbulent viscosity. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1321316
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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
    Two-dimensional electric fields and drifts near the magnetic separatrix in divertor tokamaks : 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. 1851-1857 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A two-dimensional calculation is presented for the transport of plasma in the edge region of a divertor tokamak solving continuity, momentum, and energy balance fluid equations. The model uses classical processes of parallel transport along the magnetic field and cross-field drifts together with anomalous radial diffusion, including perpendicular ion viscosity. The self-consistent electrostatic potential is calculated on both sides of the magnetic separatrix via quasineutrality and current continuity. Outside the separatrix, the model extends to material divertor plates where the incident plasma is recycled as neutral gas and where the plate sheath and parallel currents dominate the potential structure. Inside the separatrix, various radial current terms—from anomalous viscosity, collisional damping, inertia, and ∇B drifts—contribute to determining the potential. The model rigorously enforces cancellation of gyroviscous and magnetization terms from the transport equations. The results emphasize the importance of E×B particle flow under the X-point which depends on the sign of the toroidal magnetic field. Radial electric field profiles at the outer midplane show strong variation with the magnitude of the anomalous diffusion coefficients and the core toroidal rotation velocity, indicating that shear stabilization of edge turbulence can likewise be sensitive to these parameters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873488
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  • 6
    Electronic Resource
    Electronic Resource
    Enhanced thermal dissipation and the Rayleigh–Taylor instability in emulsion-like media (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 22-35 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Rayleigh–Taylor instability in a finely structured emulsion-like medium consisting of the two components of different compressibility is considered. Although the term "emulsion" is used to describe the structure of the medium, under typical conditions of pulsed fusion devices the medium is actually a plasma. The two components are chosen in such a way that their densities in the unperturbed state are approximately equal. Specific emphasis has been made on the analysis of perturbations with the scale (lambda, slash) considerably exceeding the size of the grains a. Average equations describing such perturbations are derived. The difference in compressibility of the two components leads to the formation of temperature variations at the scale a, and increases the rate of the thermal dissipation by a factor ((lambda, slash)/a)2. The strongest stabilizing effect of the thermal dissipation takes place when the heat conduction time is comparable with the instability growth rate. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872672
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  • 7
    Electronic Resource
    Electronic Resource
    Charge and current neutralization in the formation of ion rings in a background plasma (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 3383-3399 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: For typical field-reversed ion ring experiments, an intense ion beam is injected across a plasma-filled magnetic cusp and propagated into a solenoidal field downstream. The characteristic time τ satisfies 2π/Ωe(very-much-less-than)τ≤2π/Ωi and the background plasma can be modeled as an electron magnetohydrodynamic (EMHD) fluid. In the nearly collisionless regime, such that νe(very-much-less-than)Ωe, the plasma response is governed by the whistler mode. The role of the wall boundaries in such experiments to control the charge and current neutralization of the injected beam is considered for axisymmetric ∂/∂θ=0 geometry. It is found that for close enough conducting walls, such that the whistler transit time to the wall is short compared to the beam transit time, effective control of the return currents can be established such that current neutralization can be suppressed while maintaining good charge neutralization (νe is the electron collision frequency and Ωe is the corresponding gyrofrequency).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870487
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  • 8
    Electronic Resource
    Electronic Resource
    Discrete symmetries in axisymmetric toroidal plasma confinement (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 1451-1454 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Several discrete symmetry parameters characterizing axisymmetric toroidal plasmas have been introduced. For a device without up–down symmetry such parameters are S1, related to the handedness of the toroidal current, S2, related to the direction of the toroidal velocity, and S3, characterizing the handedness of the toroidal magnetic field. All these parameters can acquire values ±1, thereby making eight different combinations. For a device with up–down symmetry only the mutual orientation of the toroidal current, toroidal velocity, and toroidal magnetic field remain important. Based on the general expression for the Lagrangian for charged particles in an external magnetic field, we identify the invariance properties of this Lagrangian (and, accordingly, of plasma behavior) with respect to these transformations. Reduced plasma models, based on the Maxwell–Boltzmann equations, and on the magnetohydrodynamic equations, are also considered. An analysis of the plasma behavior in the context of the symmetry properties may be helpful in identifying the most probable theoretical models of plasma transport. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1357217
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  • 9
    Electronic Resource
    Electronic Resource
    An experimental testbed for the study of hydrodynamic issues in supernovae : The 42nd annual meeting of the division of plasma physics of the American Physical Society and the 10th international congress on plasma physics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 2446-2453 
    Details
    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
    URL: http://dx.doi.org/10.1063/1.1352594
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  • 10
    Electronic Resource
    Electronic Resource
    Simple theory of the line emission profile for the charge-exchange recombination spectroscopy method (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 1315-1320 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A systematic derivation of the distribution function of excited ions formed by charge-exchange recombination is presented. The following effects have been taken into account: (1) Finite lifetime of the excited state; (2) energy dependence of the charge-exchange reactivity; (3) nonuniformity of the neutral beam. It is pointed out that the contribution of the terms related to the ion temperature gradient has a different structure compared to the other terms, thereby allowing a direct measurement of the ion temperature gradient. Possible ways for improving the accuracy of electric field measurements are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873949
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