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  • 1
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 1971-1979 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this paper, a generalized kinetic dispersion equation that supports various hydromagnetic waves and instabilities is derived. The general dispersion equation is derived under the usual assumption of hydromagnetic perturbations [i.e., ||ω||2(very-much-less-than)Ωi2, and (kzνA/Ωi)2(very-much-less-than)β(parallel)i, where Ωi and νA are the ion gyrofrequency and Alfvén speed, respectively, and β(parallel)i is the parallel ion beta], but for arbitrary values of the quantity λi=(k⊥ρ⊥i)2/2=(k⊥νA/Ωi)2 β⊥i/2 that appears in the dielectric tensor. Here, ρ⊥i refers to the mean ion gyroradius, and β⊥i is the perpendicular ion beta. Otherwise, the dispersion equation is fairly general with no additional approximation, such as ignoring certain off-diagonal dielectric tensor elements (which is usually done in the literature) employed. In the subsequent numerical analysis, special attention is paid to the fire-hose instability in a high beta plasma. The numerical results reveal that the conventional treatment of the fire-hose instability (i.e., taking zero ion gyroradius limit at the outset) is not adequate, and that the effect of finite ion gyroradius results in a significant enhancement of the growth rate over a large range of wave numbers.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 836-853 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Analysis of the generalized cross-field current instability is carried out in which cross-field drift of both the ions and electrons and their temperatures are permitted to vary in time. The unstable mode under consideration is the electromagnetic generalization of the classical modified-two-stream instability. The generalized instability is made of the modified-two-stream and ion-Weibel modes. The relative importance of the features associated with the ion-Weibel mode and those of the modified-two-stream mode is assessed. Specific applications are made to the Earth's neutral sheet prior to substorm onset and to the Earth's bow shock. The numerical solution indicates that the ion-Weibel mode dominates in the Earth's neutral sheet environment. In contrast, the situation for the bow shock is dominated by the modified-two-stream mode. Notable differences are found between the present calculation and previous results on ion-Weibel mode which restrict the analysis to only parallel propagating waves. However, in the case of Earth's bow shock for which the ion-Weibel mode plays no important role, the inclusion of the electromagnetic ion response is found to differ little from the previous results which treats ions responding only to the electrostatic component of the excited waves.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 4 (1992), S. 3627-3637 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this paper the simultaneous nonlinear evolution of the Alfvén-ion-cyclotron and mirror instabilities driven by an anisotropic ion distribution function are studied. The ions are modeled by a bi-Maxwellian distribution function. For the sake of generality, two ion components are considered; the initially isotropic component and a population possessing a large temperature anisotropy with perpendicular temperature greater than parallel temperature. Here, perpendicular and parallel are defined with respect to the ambient magnetic field. The analysis is based on quasilinear kinetic theory. It is shown that initially, the mirror mode grows at a slightly faster rate when compared with the ion-cyclotron mode, but the subsequent evolution shows that the ion-cyclotron mode saturates at a much larger intensity. Simultaneously, large perpendicular temperature associated with the anisotropic ions is substantially reduced as the free energy is taken away by the unstable waves, while the parallel temperature increases so as to reduce the anisotropy. The initially isotropic ions, on the other hand, are also heated in the direction perpendicular to the ambient magnetic field vector.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 2124-2132 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The freshly created ions in the upstream region of the cometary bow shock usually form a ring-beam velocity distribution in the solar wind frame of reference. These newborn ions subsequently excite a variety of instabilities which in turn cause the ions to diffuse in pitch angle space to form a quasispherical shell velocity distribution. Such a process can be described by quasilinear kinetic theory. In the present paper, the detailed properties of the initial diffusion rates associated with the cometary newborn ions are studied for various physical parameters including the so-called injection angle α (that is, the average initial pitch angle associated with the ions) ranging from 0° (pure beam distribution) to 90° (pure ring distribution). It is shown that initial diffusion rates are strongly dependent upon the angle α, such that for 0°≤α≤60° (quasiparallel regime) the pitch angle diffusion rate remains relatively small, while for 60°≤α≤90° (quasiperpendicular regime) the diffusion rate increases substantially.
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 2 (1990), S. 842-844 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Detailed properties of the classical hydromagnetic Alfvén wave and the fire-hose instability, driven by an excess in the parallel energy, are well understood in the nonrelativistic regime. In this Brief Communication, the analysis is extended to the fully relativistic regime. The analysis is carried out for fully relativistic bi-Maxwellian distributions of electrons and ions (or positrons). It is shown that the relativistic effect has a non-negligible effect on the wave and stability properties of the low-frequency modes under certain conditions.
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 4858-4871 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this article we present the derivation of a generalized weak turbulence kinetic equation for unmagnetized collisionless plasmas in a uniform medium. For the sake of simplicity the present formulation assumes longitudinal electrostatic interaction only, and the effects of spontaneous thermal fluctuations are ignored. In spite of these simplifications, the present formalism represents a generalization of the existing weak turbulence theory in that a nonlinear eigenmode excited in a turbulent plasma with frequency close to twice the plasma frequency is incorporated into the discussion. Traditional weak turbulence theory emphasizes various linear and nonlinear interactions among wave modes in quiescent plasmas (i.e., Langmuir and ion-sound waves). In contrast, the present formalism describes linear and nonlinear interactions among Langmuir, ion-sound, and the new nonlinear eigenmode. Nonlinear wave kinetic equations for these modes are systematically derived, and the particle kinetic equation which generalizes the well known quasilinear diffusion equation, is also derived. © 2000 American Institute of Physics.
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 4720-4728 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The present study constitutes a continuation and improvement of the preceding work by Yoon et al. [J. Geophys. Res. 104, 19801 (1999)]. In the present discussion, an instability of Bernstein waves excited by a beam of energetic electrons is investigated. Special attention is paid to the regime where the ratio of plasma frequency, ωpe, to electron gyrofrequency, Ωe, is sufficiently higher than unity. An approximate but fairly accurate scheme is introduced to deal with the situation dictated by the condition, ωpe2/Ωe2(very-much-greater-than)1. The present investigation is motivated by the research in solar radiophysics. However, in this article the emphasis is placed on basic properties of the instability rather than its application. © 2000 American Institute of Physics.
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 2590-2595 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A recent alternative theory of electromagnetic radiation with frequency in the vicinity of plasma frequency and/or its harmonic, put forth by the present author, invokes a new type of nonlinear beam-plasma instability. The new theory was originally formulated by retaining the second-order nonlinear response of the plasma only. However, in a general nonlinear instability theory it is well known that the third-order correction can have a contribution of the same order of magnitude as the second-order nonlinearity. This article examines the validity of the original formulation of the nonlinear beam instability by reformulating the problem, keeping the full second- and third-order nonlinear responses of the plasma. In the final analysis, however, it is found that the third-order nonlinear correction can indeed be neglected, and that the original formulation of the problem is justified. © 1998 American Institute of Physics.
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3863-3881 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In a recent series of publications, a new theory of electromagnetic radiation with emission frequency close to the plasma frequency and/or its harmonic (i.e., the plasma emission) was presented. In this theory, the emission of radiation takes place as a result of excitation of long wavelength modes by a nonlinear beam-plasma instability, which are converted to radiative electromagnetic waves by a nonlinear mode conversion process. Unlike standard theories, the new theory predicts high radiation growth rate. In all the previous efforts on this theory, however, effects due to the presence of constant background magnetic field were ignored. The purpose of this article is to generalize the new theory to the case of weakly magnetized plasmas. © 1997 American Institute of Physics.
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 1285-1295 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This paper presents a quasilinear analysis of the relativistic electron cyclotron maser instability. Two electron populations are assumed: a low-temperature background component and a more energetic loss-cone population. The dispersion relation is valid for any ratio of the energetic to cold populations, and includes thermal and relativistic effects. The quasilinear analysis is based upon an efficient kinetic moment method, in which various moment equations are derived from the particle kinetic equation. A model time-dependent loss-cone electron distribution function is assumed, which allows one to evaluate the instantaneous linear growth rate as well as the moment kinetic equations. These moment equations along with the wave kinetic equation form a fully self-consistent set of equations which governs the evolution of the particles as well as unstable waves. This set of equations is solved with physical parameters typical of the earth's auroral zone plasma. © 1995 American Institute of Physics.
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