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Accueil > Séminaires et conférences > Séminaires, soutenances de thèses et HDR précédents > 2016 > Séminaires 2016 > Le jeudi 14 avril 2016 à 11h

Le jeudi 14 avril 2016 à 11h

Séminaire le jeudi 14/04/2016 en salle de conference Aile 0 (Palaiseau, en visio-conf a Jussieu).

Francesco Califano (Universite de Pise, Italie)
Titre : Vlasov-hybrid simulations of space plasma turbulence

Résume :
I will present recent numerical results on the problem of kinetic plasma turbulence at sub-ion scales. This is a hot topic in space plasmas research, in particular concerning the role of kinetic processes in regulating the cascade when turbulence crosses the ion microscopic lengths. In general, the energy injected at the fluid scales and constrained by the MHD invariants, cascades towards smaller scales eventually leading to the onset of non-MHD regimes. Ion kinetic effects come first into play before ”collisional processes” and open different channels of energy cascasde depending on the physical parameters (e.g., the plasma beta).

Using a hybrid Vlasov-Maxwell code, I will present high-resolution 2D-3V numerical simulations where turbulence is fed by an external forcing. The initial ambient magnetic field is perpendicular to the plane of the dynamics. The random forcing injects the energy on the largest wavelengths giving rise eventually to large amplitude fluctuations in the plane and making the plasma strongly inhomogeneous and turbulent. Intense current sheets are generated where magnetic reconnection occurs. We observe the interplay between turbulence and reconnection making them intimately entwined processes eventually reaching a quasi-stationary turbulent state.

We have investigated three regimes varying the plasma β and resistivity. For low-β regimes, the turbulence is dominated by whistler-like fluctuations, while for high-β regimes it is mostly driven by Alfvénic ones (both whistler and KAW turbulence are present in the two regimes, the difference being only in their relative importance). Furthermore, in the high-β plasma regime, signatures of strong coherent structures are found as well as a steepening of the magnetic energy spectra, which is probably due to a higher level of collisionless damping and to the interplay of the magnetic structures with the turbulent cascade.

Tutelles : CNRS Ecole Polytechnique Sorbonne Université Université Paris Sud Observatoire de Paris Convention : CEA
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Hébergeur : Laboratoire de Physique des Plasmas, Ecole Polytechnique route de Saclay F-91128 PALAISEAU CEDEX
Directeur de la publication : Pascal Chabert (Directeur)