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Accueil > Séminaires & Soutenances > Séminaires, soutenances de thèses et HDR précédents > 2015 > Séminaires 2015 > La mardi 17 mars à 13h30

La mardi 17 mars à 13h30

Lorenzo Matteini - Imperial College London

Ion kinetic energy conservation and magnetic field strength constancy in multi-fluid solar wind Alfvénic turbulence

Lieu : Palaiseau, salle de l’ex LIX

Résumé :
In this talk I will discuss properties of the plasma fluid motion in the large amplitude low frequency fluctuations of highly Alfvénic fast solar wind. I will show that protons locally conserve total kinetic energy when observed from an effective frame of reference comoving with the fluctuations. For typical properties of the fast wind, this frame can be reasonably identified by alpha particles, which, owing to their drift with respect to protons at about the Alfvén speed along the magnetic field, do not partake in the fluid low frequency fluctuations. Using their velocity to transform proton velocity into the frame of Alfvénic turbulence, we demonstrate that the resulting plasma motion is characterized by a constant absolute value of the velocity, zero electric fields, and aligned velocity and magnetic field vectors as expected for unidirectional Alfvénic fluctuations in equilibrium. We propose that this constraint, via the correlation between velocity and magnetic field in Alfvénic turbulence, is at the origin of the observed constancy of the magnetic field : while the constant velocity corresponding to constant energy can be only observed in the frame of the fluctuations, the correspondingly constant total magnetic field, invariant for Galilean transformations, remains the observational signature, in the spacecraft frame, of the constant total energy in the Alfvén turbulence frame.

CNRS Ecole Polytechnique Sorbonne Université Université Paris-Saclay Observatoire de Paris
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Mentions légales
Exploitant du site : Laboratoire de Physique des Plasmas, Ecole Polytechnique route de Saclay F-91128 PALAISEAU CEDEX
Hébergeur : Laboratoire de Physique des Plasmas, Ecole Polytechnique route de Saclay F-91128 PALAISEAU CEDEX
Directeur de la publication : Dominique Fontaine (Directrice)