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Author: Baumgärtel, K. × Subject: plasma ×

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Now showing 1 - 4 of 4
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    A linear model for amplitude modulation of Langmuir waves in weak electron-beam plasma interaction
    (Göttingen : Copernicus, 2013) Baumgärtel, K.
    A simple linear approach to the phenomenon of amplitude modulation of Langmuir waves in weak beam plasma interaction is presented. During the short growth phase of the instability and within the longer period after saturation, the waves are described by their linear kinetic dispersion properties.The amplitude modulation appears as result of the beating of waves with different wavelengths and amplitudes that have grown from noise in the initial phase. The Langmuir wave fields are calculated via FFT (fast Fourier transform) technique. The resulting waveforms in temporal representation are quite similar to those observed by spacecraft.
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    Ion dynamics in electron beam-plasma interaction: Particle-in-cell simulations
    (Göttingen : Copernicus, 2014) Baumgärtel, K.
    Electron beam-plasma interaction including ions is studied by particle-in-cell (PIC) simulations using a one-dimensional, electrostatic code. Evidence for Langmuir wave decay is given for sufficiently energetic beams, as in previous Vlasov-Maxwell simulations. The mechanism for the generation of localized finite-amplitude ion density fluctuations is analyzed. Amplitude modulation due to interference between the beam-generated Langmuir waves causes random wave localization including strong transient spikes in field intensity which create bursty ion density structures via ponderomotive forces. More dense beams may quench the decay instability and generate low-frequency variations dominated by the wave number of the fastest growing Langmuir mode.
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    Coherent amplitude modulation of electron-beam-driven Langmuir waves
    (Göttingen : Copernicus, 2013) Baumgärtel, K.
    A linear approach to the phenomenon of irregular amplitude modulation of beam-driven Langmuir waves, developed in a previous paper, is extended to explain periodic modulation as well. It comes about by beating of the fastest growing mode of the instability with beam-aligned plasma oscillations. They are naturally generated in a uniform domain of beam-plasma interaction prior to the onset of the instability. Particle-in-cell (PIC) simulations support the results of the linear analysis.
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    Kinetic slow mode-type solitons
    (Göttingen : Copernicus GmbH, 2005) Baumgärtel, K.; Sauer, K.; Dubinin, E.
    One-dimensional hybrid code simulations are presented, carried out in order both to study solitary waves of the slow mode branch in an isotropic, collisionless, medium-β plasma (βi=0.25) and to test the fluid based soliton interpretation of Cluster observed strong magnetic depressions (Stasiewicz et al., 200; Stasiewicz, 2004) against kinetic theory. In the simulations, a variety of strongly oblique, large amplitude, solitons are seen, including solitons with Alfvenic polarization, similar to those predicted by the Hall-MHD theory, and robust, almost non-propagating, solitary structures of slow magnetosonic type with strong magnetic field depressions and perpendicular ion heating, which have no counterpart in fluid theory. The results support the soliton-based interpretation of the Cluster observations, but reveal substantial deficiencies of Hall-MHD theory in describing slow mode-type solitons in a plasma of moderate beta.