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  • 1
    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.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 29 (1986), S. 803-809 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electron-cyclotron resonance absorption for oblique propagation at frequency significantly below the central electron gyrofrequency is considered. It is shown that the extraordinary mode for external launching is suited for additional heating in a tokamak reactor. The properties of wave damping at downshifted frequencies are discussed and are found to differ from those at f≈fc. Using the ray-tracing code, the wave damping of the e mode is investigated at high densities for which strong refraction of the wave beam occurs.
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 3982-3995 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Nonlinear interactions of tenuous electron beam, background, unmagnetized plasma, and self-consistently generated Langmuir and ion-sound waves are analyzed in the framework of plasma weak turbulence kinetic theory. Full numerical solutions of the complete weak turbulence equations are obtained for the first time, which show the familiar plateau formation in the electron beam distribution and concomitant quasi-saturation of primary Langmuir waves, followed by fully nonlinear processes which include three-wave decay and induced-scattering processes. A detailed analysis reveals that the scattering off ions is an important nonlinear process which leads to prominent backscattered and long-wavelength Langmuir wave components. However, it is found that the decay process is also important, and that the nonlinear development of weak Langmuir turbulence critically depends on the initial conditions. Special attention is paid to the electron-to-ion temperature ratio, Te/Ti, and the initial perturbation level. It is found that higher values of Te/Ti promote the generation of backscattered Langmuir wave component, and that a higher initial wave intensity suppresses the backscattered component while significantly enhancing the long-wavelength Langmuir wave component. © 2001 American Institute of Physics.
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  • 4
    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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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3091-3093 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An effective dielectric tensor for inhomogeneous magnetized plasmas was previously derived using a modified local mode approximation. We give a brief account of this derivation from a paper by Caldela Filho et al. (1989) to restate their priority. (AIP) © 1997 American Institute of Physics.
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  • 6
    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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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 2455-2462 
    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.
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 30 (1987), S. 438-441 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The power dependence of the wave damping in a tokamak plasma for arbitrary direction of propagation, mode of polarization, and wave frequency is investigated. Using a 2-D Fokker–Planck code, it is shown that the wave damping increases or decreases with the rf power depending on the velocity range of the absorbing electrons.
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 29 (1986), S. 3730-3739 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The absorption and amplification of fundamental electron cyclotron radiation in inhomogeneous, weakly relativistic, loss-cone and partially filled loss-cone plasmas, are studied for both perpendicular and oblique propagation, and the extraordinary mode is numerically analyzed. It is shown that there are situations where small changes in the distribution function may strongly affect the wave vector, and an explanation is given, pointing to the eventual relevance of the use of the full momentum distribution, along with relativistic effects, in the evaluation of both the real and imaginary part of the dielectric tensor. A model that could describe plasmas in actual situations like the thermal barriers in tandem mirror devices is presented and numerically investigated, and it is shown that particles scattered into the loss cone may play a relevant role.
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2697-2706 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This paper presents a quasilinear analysis of the relativistic electron cyclotron maser instability in which the self-consistent set of equations governing the evolution of the particle distribution function and the energy spectra of unstable waves is numerically solved for parameters typical of the Earth's auroral zone plasma, taking into account both resonant and non-resonant diffusions. The results obtained show that only 0.1%∼0.2% of the particle energy is converted into wave energy by the loss cone instability, and also show that the saturation amplitude for the extraordinary mode increases in proportion to the ratio between electron cyclotron frequency and electron plasma frequency, in agreement with previous results obtained with numerical simulations. © 1997 American Institute of Physics.
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