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Accueil > Séminaires & Soutenances > Séminaires, soutenances de thèses et HDR précédents > 2018 > Séminaires 2018 > Le jeudi 8 mars 2018 à 10h30

Le jeudi 8 mars 2018 à 10h30

Salle de réunion Jean Lascoux, aile 0, RdC

10h30 - Accueil café

11h00 - Séminaire

"What’s new about magnetic helicity ? Its properties and potential impact on solar eruption prediction"
par Etienne Pariat, LESIA, Observatoire de paris

Abstract :
Magnetic helicity is a quantity which is tightly related with the level of entanglement of magnetic field lines in a plasma. This quantity occupies a peculiar place in plasma physics : despite being one of the few invariant in ideal magneto-hydrodynamics, its estimation, in laboratory experiments, observations and even numerical domains, remains arduous. Recent developments have nonetheless allowed to initiate the systematic investigation of its properties. They reveal that magnetic helicity could be a key element to understand a central problem of solar physics : the trigger of solar eruptions.

During this seminar, I’ll first review the definition of magnetic helicity, present some of its key properties (ideal MHD conservation, inverse cascade) and expose the issues related with its actual measurement. I’ll then present the recent effort which have been carried to properly estimate this quantity in configurations that relates to natural plasmas. I’ll present results confirming the 40’s year old hypothesis of J. Taylor, that magnetic helicity is indeed conserved in non-ideal MHD even when strong magnetic reconnection is developing. Finally, I’ll present recent puzzling results from numerical experiments that shows that magnetic helicity seems to be characterize the eruptivity of a solar-like magnetized structure to erupt. Magnetic helicity thus appears as a potential key quantity for space weather prediction

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Le jeudi 8 mars 2018 à 10h30