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  • American Institute of Physics (AIP)  (42)
  • 1
    Electronic Resource
    Electronic Resource
    A fluid model for electron dynamics in the vacuum gap of a plasma opening switch (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 137-145 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A two-dimensional fluid model is developed to study the equilibrium flow of electrons in the vacuum gap between the cathode and the plasma of a plasma opening switch. The dynamics of electron flow in the vacuum gap region is illustrated by the distributions of the magnetic field, the electrostatic potential, and the electron density. The dependencies of the switch current and its interruption in the vacuum gap on the dimensions of the vacuum gap, the load impedance, and the electrostatic potential across the gap are investigated. The two-dimensional aspect of the electron flow in the vacuum gap and its effects on the performance of a plasma opening switch are emphasized.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347749
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  • 2
    Electronic Resource
    Electronic Resource
    One-dimensional intense laser pulse solitons in a plasma (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1489-1491 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A general analytical framework is developed for the nonlinear dispersion relations of a class of large amplitude one-dimensional isolated envelope solitons for modulated light pulse coupled to electron plasma waves, previously investigated numerically [Kozlov et al., Zh. Eksp. Teor. Fiz. 76, 148 (1979); Kaw et al., Phys. Rev. Lett. 68, 3172 (1992)]. The analytical treatment of weakly nonlinear solitons [Kuehl and Zhang, Phys. Rev. E 48, 1316 (1993)] is extended to the strongly nonlinear limit. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872346
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  • 3
    Electronic Resource
    Electronic Resource
    Current neutralization and focusing of intense ion beams with a plasma-filled solenoidal lens. I (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 4725-4739 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The response of the magnetized plasma in an axisymmetric, plasma-filled, solenoidal magnetic lens, to intense light ion beam injection is studied. The lens plasma fill is modeled as an inertialess, resistive, electron magnetohydrodynamic (EMHD) fluid since characteristic beam times τ satisfy 2π/ωpe,2π/Ωe(very-much-less-than)τ≤2π/Ωi (ωpe is the electron plasma frequency and Ωe,i are the electron, ion gyrofrequencies). When the electron collisionality satisfies νe(very-much-less-than)Ωe, the linear plasma response is determined by whistler wave dynamics. In this case, current neutralization of the beam is reduced on the time scale for whistler wave transit across the beam. The transit time is inversely proportional to the electron density and proportional to the angle of incidence of the beam with respect to the applied solenoidal field. In the collisional regime (νe〉Ωe) the plasma return currents decay on the normal diffusive time scale determined by the conductivity. The analysis is supported by two-and-one-half dimensional hybrid particle-in-cell simulations. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872040
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  • 4
    Electronic Resource
    Electronic Resource
    A study of the magnetic compression of energetic ion layers in conductive plasmas (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 1783-1791 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Results of a study of the magnetic compression of one-dimensional energetic ion layers in the presence of conductive background plasmas in cylindrical geometry are presented. For this, an updated hybrid (particle-ion and fluid-electron) computer model has been used. The first observation is that when the magnetic field at the wall is ramped quickly relative to the radial Alfvén wave transit time across the cylinder then a magnetic probe on axis would measure a larger field perturbation. When the wall field is ramped slowly, the layer energy increases proportionally with the external magnetic-field strength and, as expected, the layer self-field on axis does not change relative to external field. A study is also made of the effects of transient fluctuations on the layer energy when the field is ramped quickly. When the ramped field strength is small compared with the ambient field (the linear case), the average layer kinetic energy gained is not substantially different from the case where ramping is slow; however, the fluctuating energy is more than twice the average change. The interesting observation is made that the thermal spread in particle energy for a layer is not necessarily related to the strength of the self-field. This is explained in terms of the single particle motion in a self-potential well, and is different from the expected result for a two-dimensional ring.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870685
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  • 5
    Electronic Resource
    Electronic Resource
    Conventional solar flare theory re-examined : The 38th annual meeting of the Division of Plasma Physics (DPP) of the American Physical Society (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1929-1935 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Major objections are raised to the fundamental paradigm underlying conventional solar flare theory, viz., that the required free energy can be stored in situ at the requisite density in the corona in nonpotential magnetic fields by the action of photospheric convective motion, that it can be released rapidly through magnetic reconnection by a triggering event, and that a significant fraction of this energy is converted to x rays. An alternative explanation that avoids these difficulties requires that magnetic energy in the form of strongly sheared flux tubes be stored subphotospherically prior to the flare. It is the emergence of this subphotospherically stored magnetic shear energy into the photosphere and above, and its rapid conversion through internal magnetic reconnection to other forms that constitutes an actual flare. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872572
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  • 6
    Electronic Resource
    Electronic Resource
    Stability of force-free Taylor states in a new version of magnetic flux-averaged magnetohydrodynamics (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 29-34 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: It is observed that the recently developed magnetic flux-averaged magnetohydrodynamics (AMHD) [Phys. Plasmas 1, 2488 (1994)] is incompatible with Taylor's theorem, which states that the lowest-energy state of force-free equilibria based on the conservation of the helicity integral is absolutely stable for vanishingly small resistivity. By a modification of the Lagrangian from which AMHD is derived, a modified version of AMHD that is compatible with Taylor's theorem is obtained. It also provides an energy principle for examining the linear instability of resistive equilibria, which has a great advantage over resistive MHD. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871833
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  • 7
    Electronic Resource
    Electronic Resource
    Formation of field-reversed ion rings in a magnetized background plasma (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 2773-2783 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In typical field-reversed ion ring experiments, an intense annular ion beam is injected across a magnetic cusp into neutral gas immersed in a solenoidal magnetic field. In anticipation of a new experimental thrust to create strong field-reversed ion rings the beam evolution is investigated in a preformed background plasma on a time scale greater than an ion cyclotron period, using a new two and a half-dimensional (21/2-D) hybrid, particle-in-cell (PIC) code FIRE, in which the beam and background ions are treated as macro-particles and the electrons as a massless fluid. It is shown that under appropriate conditions axial beam bunching occurs in the downstream applied field and a compact field-reversed ring is formed. It is observed that the ring is reflected in a ramped magnetic field. Upon reflection its axial velocity is very much less than that expected from a single particle model due to the transfer of the mean axial momentum to the background ions. This increases the time available to apply a pulsed mirror for trapping the ring experimentally. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871175
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  • 8
    Electronic Resource
    Electronic Resource
    Kinetic theory of low-frequency cross-field instability in a weakly ionized plasma. I (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 1157-1168 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A consistent kinetic theory is developed for the description of electrons under conditions of a low-frequency two-stream E×B instability in collisionally dominated, weakly ionized plasmas. Starting from the Boltzmann collision integral, a simplified kinetic equation for the electron distribution function has been derived, which takes into account strong pitch-angle scattering of electrons by neutrals, velocity dependence of the electron–neutral collision frequency, etc. Linearized equations describing small oscillations of the electron distribution function and ion density are presented. For the asymptotic case of short waves, the dispersion relation of the E×B instability has been obtained and analyzed under conditions typical for the lower ionosphere. Under certain conditions, the rigorous kinetic consideration yields substantial changes in results compared to previous theories. The general approach may be applied to other linear and nonlinear low-frequency processes in a weakly ionized plasma. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871394
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  • 9
    Electronic Resource
    Electronic Resource
    Kinetic theory of low-frequency cross-field instability in a weakly ionized plasma. II (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 1169-1181 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The consistent kinetic approach developed in Paper I [Ya. S. Dimant and R. N. Sudan, Phys. Plasmas 2, 1157 (1995)] is applied to obtain the general dispersion relation of the two-stream E×B instability in collisionally dominated weakly ionized plasmas for wave frequencies small compared to the ion–neutral collision frequency. This dispersion relation covers the whole low-frequency band from the asymptotic short-wave limit studied in Paper I to the long-wave limit. Previous theories employing simplified kinetic theory or fluid equations for electron behavior are only correct in the long-wave limit. The principal new results are that the threshold conditions for this instability and the growth rates are altered from those predicted by earlier simplified theories. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871395
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  • 10
    Electronic Resource
    Electronic Resource
    Anomalous perturbative transport in tokamaks due to drift-wave turbulence (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 579-600 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A new method for calculating the anomalous transport in tokamak plasmas is presented. The renormalized nonlinear plasma response function is derived using the direct-interaction approximation (DIA). A complete calculation for the case of electrostatic drift-wave turbulence is presented. Explicit expressions for all coefficients of the anomalous transport matrix relating particle and heat fluxes to density and temperature gradients in the plasma are obtained. The anomalous transport matrix calculated using the DIA does not have the Onsager symmetry. As an example of application, the parameters of the Texas Experimental Tokamak (TEXT) [Nucl. Technol. Fusion 1, 479 (1981)] are used to evaluate all transport coefficients numerically, as well as the spectrum modulation. The relation between the theoretical results and the experimental data is discussed. Although this paper focuses on electron transport for simplicity, the method can also be used to calculate anomalous transport due to ion instabilities, such as the ion-temperature-gradient instability.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870803
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