Accélération et chauffage des ions lourds dans le vent solaire rapide : modélisations et comparaisons expérimentales

Abstract : Ion cyclotron resonance is used in models to provide the necessary contribution to the acceleration of the fast solar wind, and sometimes to heat the solar corona. It is often combined with an Alfvén waves turbulence cascade, the ion cyclotron waves being the high-frequency limit at which energy is dissipated in the solar plasma. These models are supported by features of the ion velocity distributions observed both in the upper corona (spectroscopically) and in the solar wind (in situ), like preferential heating as a function of the charge-to-mass ratio (q/m), anisotropies of temperature, or differential speeds.
The main purpose of this thesis is to constrain the power found in the waves and dissipated in the corona, by observing signatures of Alfvén and cyclotron waves in the lower corona (<1.5 solar radii). I studied for that the linewidths of coronal ions having different q/m, using the EUV-spectrometer SUMER (on board SOHO). The two main contributions in these linewidths (thermal and "non-thermal" Doppler effects, the latter potentially due to the presence of Alfvén waves) were separated by analysing the gradient of the widths above the solar limb. While doing so, I pointed out the importance of correcting the line profiles from the contribution of the instrumental stray light.
This study revealed two signatures of preferential heating above a coronal hole : ions having the lowest q/m are the hottest ones at the considered altitudes, and they also experience the largest heating when the altitude increases. Besides, curves of temperature as a function of q/m show a similar trend above a "Quiet Sun" region, which suggests that the cyclotron resonance is occurring at all latitudes.
Using these results, I proposed some guidelines on the modelling of energy exchanges between waves, minor ions, and protons in the corona.
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Submitted on : Saturday, March 4, 2006 - 6:49:20 PM
Last modification on : Friday, April 5, 2019 - 8:11:54 PM
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Laurent Dolla. Accélération et chauffage des ions lourds dans le vent solaire rapide : modélisations et comparaisons expérimentales. Astrophysique [astro-ph]. Université Paris Sud - Paris XI, 2006. Français. ⟨tel-00011755⟩

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