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  • 1
    Electronic Resource
    Electronic Resource
    Generalized weak turbulence theory (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 4858-4871 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1318358
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  • 2
    Electronic Resource
    Electronic Resource
    Maser-beam instability of Bernstein waves (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 4720-4728 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1313567
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  • 3
    Electronic Resource
    Electronic Resource
    On the higher-order nonlinear corrections to the theory of plasma emission by a nonlinear beam instability (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 2590-2595 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872945
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  • 4
    Electronic Resource
    Electronic Resource
    Motion of ions influenced by enhanced Alfvén waves (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 856-862 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this paper we discuss the dynamics of an ion interacting with large-amplitude Alfvén waves. The objective of the present analysis is to attain an in-depth understanding of the ion-pickup process which has been extensively studied in the literature by means of both quasilinear theory and numerical simulations. In general, results from self-consistent simulations provide a more complete picture of the ion pickup process, but details of the pickup process are not easily comprehended on the basis of these results. For this reason, the present study is carried out in which a test particle approach is used. It is found that for moderately large-amplitude Alfvén waves, an approximate analytical solution for the ion equation of motion can be obtained. This solution clarifies a number of basic issues such as (1) whether the cyclotron resonance is a necessary condition for the pickup to occur, (2) what is the role of initial ion phase space position on subsequent pitch angle scattering, and (3) how the wave amplitude affects the maximum velocity that an ion can gain along the direction of the ambient magnetic field during the pickup process. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872176
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  • 5
    Electronic Resource
    Electronic Resource
    Plasma emission by a nonlinear beam instability in a weakly magnetized plasma (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3863-3881 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872508
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  • 6
    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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  • 7
    Electronic Resource
    Electronic Resource
    Quasilinear analysis of loss-cone driven weakly relativistic electron cyclotron maser instability (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 1285-1295 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871459
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  • 8
    Electronic Resource
    Electronic Resource
    Plasma emission by a nonlinear beam instability (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 537-548 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A new theory for electromagnetic radiation emission with wave frequency at the plasma frequency and/or its harmonic (known as the plasma emission) is presented. According to the new theory, the radiation emission takes place as a result of combined effects of the excitation of electrostatic waves by a nonlinear beam instability, and the concurrent conversion into electromagnetic waves by a nonlinear mode coupling process. The underlying physical mechanism for the nonlinear beam instability is an interaction of energetic electron beam with enhanced ion-acoustic or Langmuir turbulence. The turbulence, which is treated as intrinsic in the present analysis, also gives rise to the nonlinear mode coupling process between the electrostatic and electromagnetic modes. That is, the two processes (nonlinear instability and mode coupling) occur concomitantly. An important aspect of the present theory is that the effective growth rate associated with the radiation is comparable to the usual beam–plasma (or bump-in-tail) instability growth rate, which makes the radiation emission process very efficient, a feature very different from any standard theory. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870979
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  • 9
    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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  • 10
    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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