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The Lorentz force effect on the On-Off dynamo intermittency
Alexandros Alexakis 1, Yannick Ponty 1

An investigation of the dynamo instability close to the threshold produced by an ABC forced flow is presented. We focus on the on-off intermittency behavior of the dynamo and the counter-effect of the Lorentz force in the non-linear stage of the dynamo. The Lorentz force drastically alters the statistics of the turbulent fluctuations of the flow and reduces their amplitude. As a result much longer burst (on-phases) are observed than what is expected based on the amplitude of the fluctuations in the kinematic regime of the dynamo. For large Reynolds numbers, the duration time of the ``On'' phase follows a power law distribution, while for smaller Reynolds numbers the Lorentz force completely kills the noise and the system transits from a chaotic state into a ``laminar'' time periodic flow. The behavior of the On-Off intermittency as the Reynolds number is increased is also examined. The connections with dynamo experiments and theoretical modeling are discussed.
1 :  Laboratoire de Cosmologie, Astrophysique Stellaire & Solaire, de Planétologie et de Mécanique des Fluides (CASSIOPEE)
Université Nice Sophia Antipolis (UNS) – CNRS : UMR6202 – Observatoire de la Côte d'Azur – INSU
Physique/Physique/Dynamique des Fluides

Physique/Astrophysique/Cosmologie et astrophysique extra-galactique

Science non linéaire/Dynamique Chaotique
Dynamo – On-off intermittency – MHD
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Alexakis_Ponty_onoff.ps(1.1 MB)
Alexakis_Ponty_onoff.pdf(381.5 KB)