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Theses

Étude statistique des processus de décomposition dans le plasma en amont de l'onde de choc terrestre

Abstract : This thesis addresses several topics that are related to the analysis of space plasma measurements in the terrestrial environment. The major part of the text is dedicated to the identification and the characterization of the nonlinear decay of Langmuir waves in solar wind plasmas. This decay has been proposed as one of the possible processes for saturating the beam-plasma instability, which is responsible for exciting intense electrostatic waves in the terrestrial foreshock. The Fourier spectra of the electric field observed in the foreshock frequently contain triple peak signatures, in agreement with the three waves involved in the decay. In this thesis, we show by statistical analysis of data from the CLUSTER satellites that the properties of the spectra are consistent with those of a decay process, thereby ruling out other interpretations. From a detailed analysis of the Doppler shifts of the spectral peaks, we conclude that in some cases an alternate form of the decay process takes place, where one of the product waves generated by the decay is an electron-acoustic wave. In the second part of this thesis we investigate the effect of plasma density inhomogeneities on the dynamics of the decay. A model of this modified instability is proposed and shown to agree with the observations. Finally, we present an application of nonlinear spectral models to the analysis of the energy transfers related to the decay instability in numerical simulation data. The last chapter, which is not directly related to the main subject of the thesis, presents a wavelet based technique for matching time series from multiple satellites.
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Jan Soucek. Étude statistique des processus de décomposition dans le plasma en amont de l'onde de choc terrestre. Planétologie et astrophysique de la terre [astro-ph.EP]. Université d'Orléans, 2005. Français. ⟨tel-00689867⟩

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