Coherent amplitude modulation of electron-beam-driven Langmuir waves

Baumgärtel, K.

doi:10.5194/angeo-31-633-2013

Cited by 8 publications

(17 citation statements)

References 17 publications

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“…In this section we present an alternative mechanism able to produce a spectral twin peak without decay. This mechanism, described earlier in the limit of rigid ions (Baumgärtel 2013), comes into play when a more dense beam (n b /n 0 0.05) penetrates the plasma. The frequency ω L of the fastest growing mode is then downshifted and separated from ω pe , the frequency of the k = 0 mode.…”

Section: Dense Beam Effectsmentioning

confidence: 80%

“…2005; Baumgärtel, 2013) and electrostatic Vlasov simulations (Umeda, 2006;Silin et al, 2007;Umeda, 2007;Umeda and Ito, 2008;Daldorff et al, 2011;Sauer and Sydora, 2012). Studies which include ion dynamics (in some cases with a reduced proton-to-electron mass ratio) show clearly that the heavy particles indeed contribute to the evolution of the instability.…”

Section: K Baumgärtel: Ion Dynamics In Electron Beam-plasma Interactionmentioning

confidence: 99%

“…with an arbitrary phase φ (Baumgärtel, 2013). This k = 0 mode is present from the very beginning prior to the onset of the instability, with an amplitude controlled by beam density and beam velocity.…”

Section: Simulation Modelmentioning

confidence: 99%

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Ion dynamics in electron beam–plasma interaction: particle-in-cell simulations

Baumgärtel

2014

Ann. Geophys.

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Abstract. Electron beam-plasma interaction including ions is studied by particle-in-cell (PIC) simulations using a onedimensional, 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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Section: Dense Beam Effectsmentioning

confidence: 80%

Section: K Baumgärtel: Ion Dynamics In Electron Beam-plasma Interactionmentioning

confidence: 99%

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Ion dynamics in electron beam–plasma interaction: particle-in-cell simulations

Baumgärtel

2014

Ann. Geophys.

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“…In this case, Langmuir oscillations can still be driven, but the parametric decay will be less effective. This has been confirmed by particle simulations [ Kasaba et al , ; Silin et al , ; Baumgärtel , ; Briand et al , ], where plateau distributions are formed if relaxation of electron beams with sufficiently high velocities, roughly of the order V b ≥5 V e , takes place. For lower beam velocities, the resulting distribution function becomes more like a two‐Maxwellian distribution without any plateau.…”

Section: Summary and Discussionmentioning

confidence: 70%

“…Our particular interest is the study of nonlinear parametric effects that occur due to the existence of Langmuir oscillations in plasmas after the electron beam instability has relaxed, forming a plateau in the electron distribution function. The transition from an unstable beam to a saturated state has been described in several kinetic studies using particle‐in‐cell (PIC) and Vlasov models [e.g., Kasaba et al , ; Matsukiyo et al , ; Silin et al , ; Baumgärtel , ; Briand et al , ; Sauer and Sydora , ]. The dispersion of high‐frequency electrostatic waves which belong to such plateau plasmas represents a superposition of the Langmuir mode with an electron‐acoustic mode owing to the second plasma population and has been described in former papers by us [ Sauer and Sydora , , , ].…”

Section: Plateau Plasmas and Related Mode Splittingmentioning

confidence: 99%

Parametric decay of current‐driven Langmuir waves in plateau plasmas: Relevance to solar wind and foreshock events

et al. 2017

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Langmuir amplitude modulation in association with type III radio bursts is a well‐known phenomenon since the beginning of space observations. It is commonly attributed to the superposition of beam‐excited Langmuir waves and their backscattered counterparts as a result of parametric decay. The dilemma, however, is the discrepancy between fast beam relaxation and long‐lasting Langmuir wave activity. Instead of starting with an unstable electron beam, our focus in this paper is on the nonlinear response of Langmuir oscillations that are driven after beam stabilization by the still persisting current of the (stable) two‐electron plasma. The velocity distribution function of the second population forms a plateau (index h) with a point at which ∂fh∂v∼0 associated with weak damping over a more or less extended wave number range k. As shown by particle‐in‐cell simulations, this so‐called plateau plasma drives primarily Langmuir oscillations at the plasma frequency (ωe) with k = 0 over long times without remarkable change of the distribution function. These Langmuir oscillations act as a pump wave for parametric decay by which an electron‐acoustic wave slightly below ωe and a counterstreaming ion‐acoustic wave are generated. Both high‐frequency waves have nearly the same amplitude, which is given by the product of plateau density and velocity. Beating of these two wave types leads to pronounced Langmuir amplitude modulation, in reasonable agreement with solar wind and terrestrial foreshock observations made by the Wind spacecraft.

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Current‐driven Langmuir oscillations and amplitude modulations—Another view on electron beam‐plasma interaction

Sauer

Sydora

2015

JGR Space Physics

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The origin of Langmuir amplitude modulations and harmonic waves observed in the solar wind and in planetary foreshock regions is investigated in beam plasmas where the saturation process of the beam instability is accompanied with the formation of a plateau distribution. This saturated state represents a current which is shown to drive homogeneous electric field oscillations at the plasma frequency. This simple mechanism has been ignored in most numerical studies based on Vlasov or particle-in-cell simulations because of the use of the Poisson equation which is not suitable to describe the mechanism of current drive in plasmas with immobile ions; instead, Ampere's law must be used. A simple fluid description of stable plateau plasmas, coupled with Ampere's law, is applied to illustrate the basic elements of current-driven Langmuir oscillations. If beam-generated Langmuir/electron-acoustic waves with frequencies above or below the plasma frequency are simultaneously present, beating of both wave modes leads to Langmuir amplitude modulations, thus providing an alternative to parametric decay. Furthermore, very important implications of our studies (presented separately) concern the electrostatic and electromagnetic second harmonic generation by nonlinear interaction of Langmuir oscillations with finite wave number modes which are driven by the plateau current as well.

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Coherent amplitude modulation of electron-beam-driven Langmuir waves

Cited by 8 publications

References 17 publications

Ion dynamics in electron beam–plasma interaction: particle-in-cell simulations

Ion dynamics in electron beam–plasma interaction: particle-in-cell simulations

Parametric decay of current‐driven Langmuir waves in plateau plasmas: Relevance to solar wind and foreshock events

Current‐driven Langmuir oscillations and amplitude modulations—Another view on electron beam‐plasma interaction

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