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

Sauer, K.; Sydora, R. D.

doi:10.1002/2014ja020409

Cited by 9 publications

(16 citation statements)

References 25 publications

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“…This paper represents a continuation of recent work ( Sauer and Sydora [], hereafter referred to as SS1) in which it was shown that current‐driven Langmuir oscillations play an important role in the understanding of electrostatic wave phenomena observed at beam plasma interaction in space plasmas. These oscillations arise at the electron plasma frequency ω e with wave number k = 0.…”

Section: Introductionmentioning

confidence: 99%

Current‐driven Langmuir oscillations and formation of wave packets via modulational instability: Relevance to STEREO observations

Sauer

Sydora

2016

Geophysical Research Letters

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Recently, it has been shown that Langmuir oscillations (LOs) at the plasma frequency can be driven by an electron current without any electrostatic instability. This current may appear due to a (small) drift of the whole electron population against the ions or by beam electrons after their relaxation to a plateau‐like distribution. The consequences of LOs for nonlinear wave phenomena in this scenario are studied by means of kinetic plasma simulations. It is shown that the electric field of LOs can act as a pump wave and generate Langmuir envelope solitons via the modulational instability. In this way, both counterstreaming Langmuir and ion‐acoustic waves arise with the same wave number. For solar wind conditions the Doppler shift leads to the generation of satellite peaks with frequencies symmetric around the plasma frequency. Simultaneously, a peak appears in the ion‐acoustic branch. These results agree well with recent STEREO observations in the solar wind.

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Section: Introductionmentioning

confidence: 99%

Current‐driven Langmuir oscillations and formation of wave packets via modulational instability: Relevance to STEREO observations

Sauer

Sydora

2016

Geophysical Research Letters

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“…This paper is closely related to recent work [ Sauer and Sydora , , , hereafter referred to as SS15 and SS16, respectively] which was devoted to current‐driven Langmuir oscillations at the electron plasma frequency ( ω e ) and their consequences for the interpretation of beam‐plasma interaction in the solar wind and planetary foreshock regions. Whereas in SS15 the simultaneous existence of both Langmuir oscillations and beam‐excited Langmuir waves with wave number k ∼ ω e / V b ( V b : beam velocity) as a cause for amplitude modulation has been considered, the paper SS16 is devoted to the evidence that the Langmuir oscillations which remain after beam relaxation may act as a pump wave of modulational instability by which wave packets are formed.…”

Section: Introductionmentioning

confidence: 79%

“…The distribution function of a plateau plasma can be represented as a superposition of shifted Maxwellians, as done by Silin et al []. When one takes two water‐bag distributions, one for the main population and another shifted one for the plateau electrons, as shown in Figure a, one gets according to equation (1) in Sauer and Sydora [] the electrostatic wave dispersion which is plotted in Figure b. Mode splitting is evident, resulting from the intersection of the electron‐acoustic mode (which belongs to the plateau plasma) with the Langmuir mode (of the main plasma).…”

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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“…Ignoring kinetic damping, the dispersion characteristics of Langmuir/electron‐acoustic waves in a beam/plateau plasma can be described in good approximation by fluid approach (Sauer & Sydora, ). The dispersion relation then takes the simple algebraic form

D ((),, ω, k) = 1 - \frac{{normalω}_{e}^{2}}{ω^{2} - normalγ k^{2} V_{e}^{2}} - \frac{{normalω}_{p}^{2}}{{(ω - k V_{0})}^{2} - normalγ k^{2} V_{p}^{2}} = 0,

which is known from standard textbooks.…”

Section: Modified Parametric Decay In Plateau Plasmasmentioning

confidence: 99%

“…Whereas one of the peaks was interpreted by beam excitation, for the other one different mechanisms have been considered, such as modulational instability, classical parametric decay, and particle trapping. In own studies (Baumgärtel, ; Sauer & Sydora, , ; Sauer et al, ), Langmuir oscillations driven by the beam/plateau current have been introduced as a new concept. In particular, the interpretation of Langmuir amplitude modulations in the recent paper by Sauer et al () by parametric decay of current‐driven Langmuir oscillations is very similar to the present approach.…”

Section: Relevance To Observationsmentioning

confidence: 99%

Parametric Decay of Beam‐Generated Langmuir Waves and Three‐Wave Interaction in Plateau Plasmas: Implications for Type III Radiation

et al. 2019

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Inspired by the results of particle‐in‐cell simulations on beam‐plasma interaction, we present a mechanism for the generation of radio waves in solar type III bursts which provides a closed chain of the conversion processes from beam‐generated Langmuir waves into electromagnetic emission. The mechanism is characterized by two key steps. The first is a hitherto unknown parametric decay process in which the primary wave directly decays to low‐k Langmuir waves (plasma oscillations) and ion acoustic waves. This decay becomes possible due to changes in the dispersion properties of longitudinal waves initiated by the presence of a beam or a plateau in the electron velocity distribution. A resonant three‐wave interaction is established between the beam‐induced Langmuir wave, the plasma oscillations, and the ion acoustic wave. Due to weak damping of the waves involved, this interaction persists after the beam has relaxed to a plateau and lasts as long as the latter exists. In the second step, low‐k Langmuir waves in the range of “optical wavelengths” can linearly couple to obliquely propagating radio waves at the plasma frequency in a wave number region around the cross points where quasi‐longitudinal and quasi‐transverse modes approach each other. Our model does not need the persistence of the beam and the associated instability for radiation to be produced. Although the theory is local with respect to the plasma frequency, it may open a way to overcome Sturrock's () dilemma of rapid beam relaxation on the one side and long‐lived radiation on the other. The observed frequency variation is suggested to arise by “adiabatic” motion of the beam‐created interaction region through the heliospheric plasma of decreasing electron density. Implications for the interpretation of in situ Langmuir waveforms and the diversity of their frequency spectra are discussed.

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

Cited by 9 publications

References 25 publications

Current‐driven Langmuir oscillations and formation of wave packets via modulational instability: Relevance to STEREO observations

Current‐driven Langmuir oscillations and formation of wave packets via modulational instability: Relevance to STEREO observations

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

Parametric Decay of Beam‐Generated Langmuir Waves and Three‐Wave Interaction in Plateau Plasmas: Implications for Type III Radiation

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