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  • 1
    Electronic Resource
    Electronic Resource
    Lower-hybrid-drift instability operative in the geomagnetic tail (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 3033-3043 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Motivated by recent interests in the current-driven instability as a plausible trigger mechanism for current disruption in the magnetotail, an extensive linear analysis of the lower-hybrid-drift instability (LHDI) in a high plasma beta regime is conducted. In the theoretical formulation, the fundamental difference between this instability and the modified-two-stream/ion-Weibel instability is clarified. Numerical solutions of the dispersion equation for the LHDI are obtained for plasma parameters appropriate for the magnetotail. In spite of the tendency for the LHDI to be stabilized at high plasma beta, the near-Earth current sheet environment immediately before the onset of current disruption is found to be just above the unstable threshold of the LHDI. The stability analysis is further extended to a model two-dimensional current sheet of Lembège and Pellat, with parameters chosen to match the near-Earth current sheet at the critical time. It is found that the LHDI is operative over an entire current sheet, thus providing theoretical support for the plausibility that the LHDI may play a significant role in triggering current disruption in the magnetotail.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870496
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  • 2
    Electronic Resource
    Electronic Resource
    Plasma emission via a beam instability with density modulation (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 76-89 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this article, a new emission process for radiation near the plasma frequency in an unmagnetized plasma (i.e., the plasma emission) is discussed. The process involves a tenuous beam of energetic electrons and low-frequency ion waves. The key point is that the ion waves can modulate the thermal electron density so that the condition for beam–plasma interaction (ω=k⋅V, where V is the average beam velocity) is Doppler shifted in wave vector space in accordance with the wavelength that characterizes the ion density fluctuations [ω+ω'=(k+k')⋅V, where ω' and k' are the characteristic frequency and wave vector associated with the ion wave; in the present discussion, let set ω'=0]. As a result, the unstable electrostatic beam–plasma mode becomes coupled with the fast electromagnetic mode. Consequently in an inhomogeneous plasma the amplified waves can naturally change to electromagnetic mode and escape from the source region.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870463
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  • 3
    Electronic Resource
    Electronic Resource
    Quasilinear evolution of Alfvén-ion-cyclotron and mirror instabilities driven by ion temperature anisotropy (1992)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 4 (1992), S. 3627-3637 
    Details
    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
    URL: http://dx.doi.org/10.1063/1.860371
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  • 4
    Electronic Resource
    Electronic Resource
    Quasilinear diffusion rates of cometary ions (1991)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 2124-2132 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859625
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  • 5
    Electronic Resource
    Electronic Resource
    Gyroharmonic maser instability for weakly relativistic electrons with a loss-cone distribution (1990)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 2 (1990), S. 1918-1927 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The weakly relativistic dielectric tensor for a system of electrons comprised of cold and energetic populations, embedded in a neutralizing background, is reformulated in terms of an infinite series representation in powers of λ=αck⊥/ωc, where α2 is a parameter proportional to the average thermal energy of the energetic electrons, k⊥ is the perpendicular component of the wave vector k, and ωc is the electron gyrofrequency. The energetic electrons are assumed to have a loss-cone feature in the perpendicular momentum space. The present formalism can be used in the problem of cyclotron maser (i.e., emissions near the fundamental ω≈ωc) as well as more general gyroharmonic maser (i.e., multiharmonics) emissions resulting from weakly relativistic loss-cone electrons. This is because, unlike the previous theories in which certain approximations such as the single-harmonic approximations are made, the present formalism retains contributions from the entire harmonics. As a result, the present formalism is valid for arbitrary ωp/ωc, where ωp is the total electron plasma frequency. As an application, growth rates for the X-mode and Z-mode gyroharmonic maser instabilities are calculated for a propagation angle θ=90° at various energies, and for ωp/ωc ranging from 0.1 to 1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859463
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  • 6
    Electronic Resource
    Electronic Resource
    Electromagnetic fire-hose instability in a fully relativistic bi-Maxwellian plasma (1990)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 2 (1990), S. 842-844 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859568
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  • 7
    Electronic Resource
    Electronic Resource
    Transition from reactive to kinetic electromagnetic instabilities generated by ring-beam ions (1991)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 2455-2462 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The dispersion relation for the low-frequency electromagnetic waves propagating parallel to the ambient magnetic field is studied for a plasma comprised of energetic ring-beam distribution of ions and a background population. Detailed properties of the dispersion relation are studied for various physical parameters with particular emphasis placed on the transition from the cold case to the thermal regime. In addition, the stability characteristics are investigated for different values of α, where tan α is the ratio between the ring and the beam velocity, ranging from α=0 (pure beam) to α=90° (pure ring). The unstable modes are studied in further detail, and the dependence of the growth rate on several parameters, such as the density of the ring-beam ions and thermal speeds associated with the background and the ring-beam ions, is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859617
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  • 8
    Electronic Resource
    Electronic Resource
    Effect of finite ion gyroradius on the fire-hose instability in a high beta plasma (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 1971-1979 
    Details
    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
    URL: http://dx.doi.org/10.1063/1.860785
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  • 9
    Electronic Resource
    Electronic Resource
    Nonlinear analysis of generalized cross-field current instability (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 836-853 
    Details
    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
    URL: http://dx.doi.org/10.1063/1.860935
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  • 10
    Electronic Resource
    Electronic Resource
    Ion heating by kinetic cross-field streaming instability due to reflected ions at a quasiperpendicular shock (1992)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 4 (1992), S. 719-729 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The present paper shows that the reflected ion at a supercritical quasiperpendicular shock wave can excite a purely growing m9de propagating parallel to the ambient magnetic field (k(parallel)B0). To discuss the ion heating by such an unstable mode, the self-consistent quasilinear kinetic equation is solved with the assumption that the present purely growing mode is the dominant unstable mode in the system. In the quasilinear analysis of the instability, two particular cases are considered—the case of low initial ion beta [βi(0)=0.1] and that of a high initial ion beta [βi(0)=1]. For each case of low and high initial betas, two values of initial turbulence level are used. One corresponds to δB2(0)/B20=0.1 and the other corresponding to δB2(0)/B20 =0.1. It is shown that for both low and high beta cases, the ion heating at the shock becomes more efficient for a higher value of δB2(0)/B20.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860270
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