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  • 1
    Electronic Resource
    Electronic Resource
    Experimental study of fluctuations excited by a narrow temperature filament in a magnetized plasma (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 1397-1407 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A systematic study is made of the spontaneous growth of fluctuations in temperature, density, and magnetic field in a narrow (on the order of the electron skin depth) field-aligned temperature filament embedded in a large magnetized plasma. Two broad classes of fluctuation ("low" and "high" frequency modes) have been identified and studied in detail. A high-frequency drift-Alfvén mode grows at frequencies about one tenth the ion gyrofrequency in the region of the filament where the temperature gradient is large. The measured radial profiles of the density and magnetic field fluctuations associated with this mode agree well with theoretical predictions. The high-frequency mode has been observed to exhibit several interesting nonlinear features, including steepening wave form, progression in azimuthal mode number, coupling to the low frequency mode with subsequent sideband generation, and eventually a transition to broad band turbulence. The nature of the low-frequency mode which has frequencies about one fiftieth of the ion gyrofrequency is less certain, but it has been identified as a spatially localized, azimuthally symmetric mode consisting primarily of temperature fluctuations. Both the high and low-frequency modes give rise to electron heat transport at rates in excess of the classical values. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873957
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  • 2
    Electronic Resource
    Electronic Resource
    Experimental study of classical heat transport in a magnetized plasma (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 544-553 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A systematic study is made of the axial and transverse heat transport that arises when a microscopic temperature filament is generated, under controlled conditions, in a magnetized plasma of large dimensions. For early times and relatively small temperature gradients the study conclusively demonstrates the two-dimensional pattern characteristic of the classical theory based on Coulomb collisions. The full nonlinear dependence of the transverse and axial electron heat conductivities is sampled through temperature changes in the range δTe/Te∼1–10. The dependence on the confining magnetic field is explored over a factor of 3 (∼ factor of 10 in transverse conductivity). It is found that under quiescent conditions, the observed behavior agrees with classical theory within the experimental uncertainties. However, over long times and/or for steep temperature gradients, fluctuations develop spontaneously and cause a significant departure from the predictions of the classical theory. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873840
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  • 3
    Electronic Resource
    Electronic Resource
    Possibility of detecting magnetospheric radio bursts from Uranus and Neptune (1976)
    [s.l.] : Nature Publishing Group
    Nature 261 (1976), S. 299-301 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Table 1 Values ; for quantities us ;ed in estimating the detectability of Ml RJBs are listed foi r each of the planets *P (gauss) BE ode (gauss) PN^N W* IV p Peak frequency (W) (MHz) Peak power flux at Earth (Wm2Hz) Total radiated power (W) Earth Jupiter Saturn Uranus ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/261299a0
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  • 4
    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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  • 5
    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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  • 6
    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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  • 7
    Electronic Resource
    Electronic Resource
    Nonlinear Landau damping of resonantly excited fields in nonuniform plasmas (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 567-578 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this study the resonant excitation of a nonuniform plasma by two electromagnetic waves at closely spaced frequencies ω1, ω2 with ω1(approximately-greater-than)ω2 is considered. Each of the pump waves excites a Langmuir wave at the point in the density profile, where plasma resonance is achieved. For profiles having scale lengths L large compared to the characteristic Airy scale length (i.e., kAL(very-much-greater-than)1) the linear Landau damping of the Langmuir waves is quite small close to their cutoff, hence the beat interaction with slow electrons plays an important role. The problem is formulated in terms of differential equations in configuration space for the waves at ω1, ω2, which are coupled to the idler field at ω1−ω2. The idler is described kinetically by a differential equation in Fourier space. The interaction is governed by the parameter ω˜3=(1−ω2/ω1)kAL and the scaled pump strength. For ω˜3(very-much-less-than)1 the ponderomotive nonlinearity is recovered and a dissipative contribution is obtained. For ω˜3(approximately-greater-than)1 plasmon transfer from ω1 to ω2 causes strong depletion of the high-frequency wave before significant ponderomotive profile changes set in. The fractional power absorbed through the idler is smaller than the power transferred to ω2 by a factor of (1−ω2/ω1).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870802
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  • 8
    Electronic Resource
    Electronic Resource
    Structure of Alfvén waves at the skin-depth scale (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 3765-3774 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This analytical study demonstrates that shear Alfvén waves having transverse scale on the order of the electron skin depth exhibit a collisionless divergence determined by propagation cones that emanate from the edges of the exciting structures. Axial current channels are found to spread radially due to the skin effect up to the cone trajectories and at distances of a few wavelengths from the exciter develop radial diffraction patterns. For values of the collision frequency slightly larger than the wave frequency resistive diffusion allows the axial currents to expand beyond the cone trajectories. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870850
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  • 9
    Electronic Resource
    Electronic Resource
    Drift-Alfvén fluctuations associated with a narrow pressure striation (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 144-157 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This analytical and numerical study illustrates the linear stability properties of low frequency electromagnetic eigenmodes driven by field-aligned pressure striations whose scale transverse to the confining magnetic field is on the order of the electron skin-depth. A full electromagnetic formulation is given in terms of the coupling of the fluctuating axial fields (E˜z,B˜z) and incorporates shear and compressional Alfvén waves, drift waves, and ion acoustic waves. The kinetic response of the electrons includes pitch-angle scattering (Lorentz model) and the ions are treated as a magnetized, cold fluid. Detailed quantitative comparisons of the theoretical predictions are made with laboratory observations of fluctuations generated in controlled pressure depletions [J. E. Maggs and G. J. Morales, Phys. Plasmas 4, 290 (1997)] and in narrow temperature plumes [A. T. Burke, J. E. Maggs, and G. J. Morales, Phys. Rev. Lett. 81, 3659 (1998)]. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873789
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  • 10
    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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