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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 449-462 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Motivated by conditions in the terrestrial foreshock, the mode conversion process in the inner region for a weakly magnetized plasma with a longitudinal linear density profile is examined. Coupled differential equations are employed to describe the wave energy coupling and the mode structure of electrostatic Langmuir and upper-hybrid branches, and electromagnetic O, X, and Z modes. For an incident electrostatic wave (the "inverse" problem), the coupled equations are solved using Green's function method, and the mode conversion coefficient is determined from the asymptotic solutions. In the limit of a vanishing magnetic field, solutions converge to previous unmagnetized solutions. It is found that the magnetic field narrows the window of conversion and reduces the angles of propagation of electromagnetic waves with respect to the magnetic field, in agreement with results from previous solutions (of the "direct" problem) for a magnetized cold plasma. The narrowing of the window occurs at angles of propagation larger than the angle corresponding to the maximum conversion. © 1999 American Institute of Physics.
    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. 3148-3162 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The modulational instability and collapse of waves in the vicinity of the lower-hybrid resonance including both magnetosonic and lower-hybrid waves are investigated by analytical and numerical methods. The mechanism leading to the modulational instability is the nonlinear coupling of lower-hybrid waves with the much lower-frequency quasineutral density perturbations via the ponderomotive force. The result is a filamentation of the high-frequency field producing elongated, cigar-shaped nonlinear wave packets aligned along the magnetic field with the plasma expelled outside (cavities). The analytical self-similar solutions describing cavity collapse are obtained and compared with the results of numerical simulation for both two- and three-dimensional cavity geometries. It is shown that in three-dimensional solutions the transverse, with respect to the magnetic field, contraction remains prevailing. The possibility of ion acceleration as the result of the lower-hybrid collapse is discussed and detailed comparison is made with the observations of the phenomena in the auroral ionosphere.
    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. 1092-1101 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A comparison is made between the properties of the low-frequency, long-wavelength velocity-shear-driven instability in kinetic theory and magnetohydrodynamics (MHD). The results show that the removal of adiabaticity along the magnetic field line in kinetic theory leads to modifications in the nature of the instability. Although the threshold for the instability in the two formalisms is the same, i.e., VA(parallel)〈V0〈Cs, the kinetic growth rate and the unstable range in wave-number space can be larger or smaller than the MHD values depending on the ratio between the thermal speed, Alfvén speed, and flow speed. When the thermal speed is much larger than the flow speed and the flow speed is larger than the Alfvén speed, the kinetic formalism gives a larger maximum growth rate and broader unstable range in wave-number space. In this regime, the normalized wave number (kL) for instability can be larger than unity, while in MHD it is always less than unity. The normal mode profile in the kinetic case has a wider spatial extent across the shear layer.
    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 2 (1990), S. 488-494 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The evolution of an equilibrium consisting of two magnetic islands with oppositely directed currents embedded in a strong magnetic field is investigated, using numerical simulation methods. The rapid development of an ideal magnetohydrodynamic instability is observed, which first rotates and then expels the islands. The growth rate is on the order of the inverse of the Alfvén transit time and is much higher than that for magnetic island coalescence. In the nonlinear stage, resistivity becomes important as the reconnection process ensues and dissipates the magnetic energy. The growth rate of the instability is a weak function of the plasma beta and other plasma parameters such as S, the magnetic Reynolds number. An energy principle analysis, based on eigenfunctions obtained from the simulation, confirms the existence of the instability.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 4 (1992), S. 3562-3568 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This paper presents a model of beam–plasma discharge resulting from the quasilinear heating of plasma electrons by Langmuir waves which are excited by beam–plasma interactions. The heating is made possible by the spectral transformation of waves propagating radially from the central beam-occupied region toward the region of lower plasma density. In this paper equations describing the wave spectral density, the distribution function of a high-energy electron tail, and its stationary density profile are obtained and numerically solved; to do so a balanced diffusion and ionization is assumed. The possibility of significant plasma density enhancement in beam–plasma discharge is demonstrated.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 30 (1987), S. 200-208 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Propagation of a nonrelativistic electron beam in a plasma in a strong magnetic field has been studied using electrostatic one-dimensional particle simulation models. Electron beams of finite pulse length and of continuous injection are followed in time to study the effects of beam–plasma interaction on the beam propagation. For the case of pulsed beam propagation, it is found that the beam distribution rapidly spreads in velocity space generating a plateaulike distribution with a high energy tail extending beyond the initial beam velocity. This rapid diffusion takes place within a several amplification length of the beam–plasma instability given by (ωpω2b) −1/3V0, where ωp, ωb, and V0 are the target plasma, beam–plasma frequencies, and the beam drift speed. This plateaulike distribution, however, becomes unstable as the high energy tail electrons free-stream, generating a secondary beam. A similar process is observed to take place for the case of continuous beam injection when the beam density is small compared with the total density nb/nt〈1. In particular, the electron velocity distribution is found monotonically decreasing in energy, having a high energy tail whose energy reaches twice the initial beam energy. Such an electron distribution is also seen in laboratory experiments and in computer simulations performed for a uniform, periodic system. When the beam density is increased so that the beam current exceeds the thermal return current, enbV0(approximately-greater-than)enevt, where ne and vt are the density and thermal speed of the ambient electrons, beam propagation becomes much slower due to the electric field generated by the excess charges associated with the beam electrons.Beam electrons are reflected from the ambient plasma as if they are bouncing off a rigid wall. When the beam velocity is increased while holding the beam density constant, simulations show that the beam current can exceed significantly the return current generated by the thermal electrons enevt. It is shown that the electric field generated by the beam–plasma instability accelerates the ambient electrons opposite to the beam propagation, thereby enhancing the return current.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Advances in Space Research 8 (1988), S. 157-160 
    ISSN: 0273-1177
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Advances in Space Research 8 (1988), S. 137-149 
    ISSN: 0273-1177
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Advances in Space Research 11 (1991), S. 183-187 
    ISSN: 0273-1177
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Planetary and Space Science 18 (1970), S. 1799-1812 
    ISSN: 0032-0633
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
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