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  • Other Sources  (19)
  • 1
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    On the generation of broadband electrostatic noise (1987)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Linear theory analysis and particle simulation studies were carried out to understand the mechanisms generating broadband electrostatic noise (BEN) and the effects of BEN on particles as well as the nonlinear saturation level in the geomagnetic tail region. Streaming ion beams as well as warm ions and electrons are used to model the plasma-sheet particle population. When the beam ion temperature is comparable to the temperature of the warm plasma-sheet particles, electrostatic ion cyclotron instabilities become unstable, giving rise to low-frequency noise at omega less than about n(Omega i), where Omega i is the ion gyrofrequency.
    Keywords: GEOPHYSICS
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  • 2
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    Acceleration of hydrogen ions and conic formation along auroral field lines (1983)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Electrostatic ion cyclotron turbulence and the formation of ion conics at low altitudes (about 1500 km) along auroral field lines have been investigated analytically and by plasma numerical simulations. Ion cyclotron waves are assumed to be driven unstable by the upgoing cold ionospheric electrons associated with the downward auroral current. When the electron drift speed is comparable to the electron thermal speed, it was found that the large-amplitude (the saturation level is approximately equal to unity) coherent (omega equals the ion gyrofrequency) ion cyclotron waves should exist along auroral field lines at low altitudes extending a few hundred kilometers. Ion conics are associated with ion cyclotron turbulence, and the ion bulk temperature is found to increase by a factor of 10 from the initial ionospheric temperature, while the temperature of the high-energy tail can be as much as 100 times the ionospheric temperature. Theory and simulations are in good agreement.
    Keywords: GEOPHYSICS
    Type: AD-A137245 , AFGL-TR-84-0016 , Journal of Geophysical Research; 88; Feb. 1
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  • 3
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    Ion-beam-driven electrostatic ion cyclotron instabilities (1983)
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    Publication Date: 2019-06-28
    Description: Results are presented of a particle simulation study of the electrostatic ion-cyclotron (EIC) instability driven by a parallel ion beam. The results of this simulation study demonstrate the nonlinear consequences of nonresonant EIC waves destabilized by an ion beam parallel to the magnetic field for the case of a large beam velocity. As a consequence of the instability, it is shown that the beam ions are heated strongly in the perpendicular direction and suffer a strong anomalous friction via EIC waves which leads to the beam slowing down. Simulation results indicate that the anomalous slowing down of beam ions by EIC waves is much larger than that from the classical electron-drag, and the perpendicular collision frequency measured from perpendicular beam heating is as large as that from Bohm diffusion. It is concluded that the ion beam driven EIC wave is a viable mechanism for the transfer of ion parallel beam energy to the ion perpendicular energy.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 10; April 19
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  • 4
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    Liquid helium cooled Fabry-Perot spectrometers (1986)
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    Publication Date: 2019-06-28
    Description: An account is given of two successful efforts to construct cryogenic Fabry-Perot interferometers that are sufficiently compact and stable for such harsh conditions as those of balloon or space observations, as well as ground-based ones. Attention is given to the design features and performance of a Fabry-Perot interferometer incorporating an electromagnet actuator, the ISAS interferometer, a Fabry-Perot spectrometer with superconducting actuators, and the University of Arizona interferometer.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
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  • 5
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    Formation of a conical distribution and intense ion heating in the presence of hydrogen cyclotron waves (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: In the considered investigation, it is assumed that the field aligned currents are responsible for producing electrostatic harmonic cyclotron waves (EHC). Using a one-dimensional simulation model in which the electron velocity distribution is maintained by a constant injection of the initial distribution, it is shown that, in contrast to earlier initial value simulations, EHC waves grow to a large amplitude, resulting in the formation of an anisotropic ion velocity distribution. Both the heating rate and the anisotropy are in reasonable agreement with the quasi-linear theory, taking into account the cyclotron resonance. The results show that the saturation is due to the combined effects of wave induced diffusion in an electron velocity space and the heating of ions perpendicularly. Both these effects reduce the growth rate.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters; 8; July 198
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  • 6
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    Acceleration of heavy ions on auroral field lines (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Results of both a linear and a nonlinear study of oxygen cyclotron waves and the associated oxygen heating are presented. Linear theory predicts that oxygen cyclotron waves will have smaller growth rates than hydrogen cyclotron waves. Results of a simulation study in which the free energy source is an initial drifting electron distribution indicate that oxygen cyclotron waves only grow to small amplitudes, while the hydrogen cyclotron waves achieve larger amplitudes. In an attempt to model more realistically the continuous ionospheric outflow, a simulation model is used, in which the electron velocity distribution is maintained by a constant flow of electrons. This latter model predicts that the oxygen waves grow to amplitudes much larger than the hydrogen waves resulting in the preferential heating of the heavier ions.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters; 8; July 198
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  • 7
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    Plasma physics on auroral field lines - The formation of ion conic distributions (1983)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The formation of the conical distribution function and the acceleration of ions on aurora field lines are considered. Ion cyclotron waves were assumed to be excited by drifting electrons associated with the return current in the auroral zone. A theoretical analysis of ion cyclotron waves is given, and a simulation model is described. Simulation results are presented. The heating of ions and the evolution of ion cyclotron waves on auroral field lines and in the magnetosphere are discussed.
    Keywords: GEOPHYSICS
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  • 8
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    Generation of ordinary mode electromagnetic radiation near the upper hybrid frequency in the magnetosphere (1984)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: It is shown by means of plasma numerical simulations that long-wavelength ordinary mode electromagnetic radiation can be generated from short-wavelength electrostatic waves near the upper hybrid resonance frequency in an inhomogeneous plasma. A possible relation of this process to nonthermal continuum radiation in the magnetosphere is discussed.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 89; 9125-913
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  • 9
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    Transverse acceleration of ions on auroral field lines (1983)
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    Publication Date: 2019-06-28
    Description: This paper examines transverse ion heating on auroral field lines associated with current-driven electrostatic ion cyclotron waves theoretically and by numerical simulations. The auroral plasma is assumed to consist of drifting electrons and stationary hydrogen and oxygen ions. Depending on the ratio of the electron drift speed to the thermal speed and the ratio of hydrogen to oxygen concentrations, preferential heating of either hydrogen or oxygen ions can take place. It is found that unless the oxygen ions are a minority species, oxygen transverse heating generally exceeds that of hydrogen ions. Theory and numerical simulations are in good agreement.
    Keywords: GEOPHYSICS
    Type: AFGL-TR-84-0015
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  • 10
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    Turbulent heating of heavy ions on auroral field lines (1984)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Electrostatic ion cyclotron turbulence and the associated acceleration of ions on auroral field lines are investigated analytically and by plasma simulations. The auroral plasma is assumed to consist of drifting electrons and stationary hydrogen and oxygen ions. It is found that for a given critical drift, the maximum ion perpendicular heating is generally larger for oxygen ions than for hydrogen ions. Simulation results show that unless the oxygen ions are a minority species, oxygen transverse heating generally exceeds that of hydrogen ions. Theory and numerical simulations are in good agreement.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 89; 2235-225
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