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Conference papers

On the mechanism of radio emission in type III Solar Radiobursts

Abstract : Solar radio emissions of the type III are between the most intense in the solar system. It is known that they are generated by intense fluxes of energetic electrons ejected by the Sun into heliosphere during periods of the of the solar activity. It is accepted that the process of generation of radiowaves occurs in two steps. First, electron beams generate electrostatic Langmuir waves and then these waves due to some, supposed to be non-linear, process generate electromagnetic emissions. Recent studies showed that the level of density fluctuations in the solar wind is so high and they significantly affect beam plasma interaction. The effect of random density fluctuations for Langmuir waves propagating in a solar wind consists in strong variations of their phase velocity. These variations suggest that wave resonate with particles having different velocities. This results in significant decrease of the instability increment and an increase of the relaxation length of a beam. These processes were studied analytically and using computer simulations. The results of modelling were shown to reproduce the majoriity of waveforms observed on satellites Wind and Stereo. Statistical characteristics of wave amplitudes in simulations are very similar with observations. We show here that intense density fluctuations not only crucially influence the beam plasma interaction but also change the mechanism of energy transformation from electrostatic waves into electromagnetic. It is known that reflection of Langmuir waves from the density inhomogeneities under certain conditions may result in partial transformation of thergy of electrostatic wave into electromagnetic. This effect was studied in application to laser-plasma interaction and in ionospheric heating. We consider this same effect of linear wave energy transformation in application to generation of type III Solar radio bursts. We use the probability distribution of density fluctuations to evaluate an efficiency of this process and to determine its statistical characteristics. We show that for the level of fluctuations of the order of 1% the mechanism of linear transformation of electrostatic waves energy into electromagnetic may be significantly more efficient than the process of nonlinear conversion of Langmuir waves by means of coupling with the ion-sound waves.
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https://hal-insu.archives-ouvertes.fr/insu-03565544
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Submitted on : Friday, February 11, 2022 - 8:59:28 AM
Last modification on : Tuesday, May 10, 2022 - 3:24:58 PM

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V. Krasnoselskikh, A. Voshchepynets, E. Kontar, M. Maksimovic. On the mechanism of radio emission in type III Solar Radiobursts. American Geophysical Union, 2018, San Francisco, United States. pp. 10. ⟨insu-03565544⟩

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