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  • 1995-1999  (4)
  • 1985-1989  (3)
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  • 1
    Electronic Resource
    Electronic Resource
    Laboratory studies of field-aligned density striations and their relationship to auroral processes : The 38th annual meeting of the Division of Plasma Physics (DPP) of the American Physical Society (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1881-1888 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Magnetic field-aligned structures in current, density, and temperature are common features of the auroral ionospheric plasma. These structures both generate and transform low frequency waves in the plasma. The results of laboratory studies of two processes involving magnetic field-aligned density depletions (striations) that play a role in auroral plasma dynamics are presented. The first process involves the spontaneous generation of density and magnetic fluctuations at the striation edge. The nature of the fluctuations depends upon the electron plasma beta. At high beta (greater than the electron to ion mass ratio, m/M) the drift Alfvén wave is excited. At lower beta the density and magnetic field fluctuations separate and the shear Alfvén wave dominates. This process creates an environment conducive to electron acceleration along the magnetic field when the striation size is on the order of the electron skin depth because the shear Alfvén wave then has a substantial field-aligned electric field. The second process is the direct conversion of electromagnetic whistler waves to electrostatic lower hybrid waves at the striation edge. This process provides a mechanism for concentrating lower hybrid wave energy in the vicinity of striations where it may play a role in electron and ion heating. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872331
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Structure of kinetic Alfvén waves with small transverse scale length (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 4118-4125 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This analytical study illustrates the spatial pattern of kinetic Alfvén waves excited by a current-modulating disk whose dimension a, transverse to the confining magnetic field, is comparable to the ion sound gyroradius cs/Ωi, where cs is the sound speed and Ωi the ion cyclotron frequency. The radial structure of the wave azimuthal magnetic field is found to consist of four regions: a Bessel function behavior for r〈a, a near null at r≅a, and a driven Airy pattern for r(very-much-greater-than)a which merges onto the 1/r asymptotic region. The pattern spreads at an angle given by tan θ=(ω/Ωi)(cs/vA)/2.6, where ω is the modulation frequency and vA is the Alfvén speed. This behavior arises because there is a maximum value at finite k⊥ for the ratio of the perpendicular to parallel group velocity, which differs from the cone spreading [G. J. Morales et al., Phys. Plasmas 1, 3765 (1994)] associated with inertial Alfvén waves. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872531
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Properties of drift waves in a filamentary density depletion (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 555-565 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This analytical and numerical study explores the properties of electrostatic, drift-wave eigenmodes trapped within a magnetic field-aligned depletion in plasma density and temperature whose transverse dimension is on the order of the electron skin depth. The dependence of the complex eigenfrequencies on key parameters is investigated for collisionless and collisional plasma. The collisional description is based on the Lorentz model of electron pitch-angle scattering. The separate roles of the gradients in density and temperature are illustrated for the collisional and collisionless regimes. The predictions are compared to experimental observations [J. E. Maggs and G. J. Morales, Geophys. Res. Lett. 23, 633 (1996); Phys. Plasmas 4, 290 (1997)] of a controlled striation in the laboratory. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872153
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  • 4
    Electronic Resource
    Electronic Resource
    Fluctuations associated with a filamentary density depletion (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 290-299 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Density and magnetic fluctuations arising spontaneously in a narrow field-aligned density striation in a magnetized discharge He plasma are found to exhibit a radial eigenmode structure. The nature of the fluctuations depends upon the electron plasma beta, βe. For βe greater than the electron to ion mass ratio (βe〉m/M) the frequency spectrum exhibits sharply peaked eigenfrequencies with the density and magnetic fluctuations strongly coupled so that the growing mode is identified as the drift-Alfvén wave. For βe less than the mass ratio (βe〈m/M) the density and magnetic fluctuations separate in frequency and broadband magnetic shear Alfvén wave turbulence develops. The driving source for the fluctuations is the cross-field density and temperature gradients in the edge of the striation which have scale lengths on the order of the electron skin depth. The fluctuations associated with the striation are compared to the edge fluctuations of the plasma column which are found to exhibit a universal exponential frequency spectrum. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872089
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    Self-consistent modification of a fast-tail distribution by resonant fields in nonuniform plasmas (1988)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 31 (1988), S. 1471-1480 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An analytic study is made of the second-order modifications produced on the fast-tail electron distribution function of a nonuniform plasma subjected to resonant excitation by wave sources. The source models considered can represent excitation by external electromagnetic waves propagating obliquely to the plasma density gradient, mode conversion of electrostatic whistlers, beat of two transparent electromagnetic waves, and direct conversion from ripples in the density profile. The calculation treats the Landau damping provided by fast-tail electrons self-consistently and is applicable to plasmas having a long density scale length L, i.e., (kDL)1/3 (very-much-greater-than)1, where kD is the Debye wavenumber of the warm background electrons. A threshold condition is found for the formation of a positive slope in the tail distribution by the various excitation mechanisms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.866738
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    Paper (German National Licenses)
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  • 6
    Electronic Resource
    Electronic Resource
    Generation of Alfvén waves caused by thermal modulation of the electrical conductivity (1985)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 28 (1985), S. 2458-2465 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An analytic study is made of the effects produced by a localized modulation of the electrical conductivity of a magnetized plasma carrying a field-aligned current. The modulation is assumed to be caused by a heating source external to the plasma. The formulation used is applicable to modulation frequencies ω below the ion-cyclotron frequency ωci, and permits the calculation of the radiation pattern which contains shear as well as compressional Alfvén modes and near fields. For ω/ωci(very-much-less-than)1, the radiation appears primarily in the form of a highly collimated shear mode traveling along the field lines passing through the spot where the modulation occurs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.865254
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    Paper (German National Licenses)
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  • 7
    Electronic Resource
    Electronic Resource
    Heating efficiency of beat-wave excitation in a density gradient (1988)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 31 (1988), S. 3807-3808 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A simple model is presented that yields analytical expressions for the heating efficiency of beat-wave excitation in a plasma with a linear density profile. The effect of self-consistent Landau damping by tail electrons is included without recourse to WKB approximations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.866849
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    Paper (German National Licenses)
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