The Lorentz force effect on the On-Off dynamo intermittency

Alexandros Alexakis (1) , Yannick Ponty (1)

1 CASSIOPEE - Laboratoire de Cosmologie, Astrophysique Stellaire & Solaire, de Planétologie et de Mécanique des Fluides

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.

Mots clés: Dynamo; On-off intermittency; MHD

Domaines: Dynamique des Fluides [physics.flu-dyn]; Cosmologie et astrophysique extra-galactique [astro-ph.CO]; Dynamique Chaotique [nlin.CD]

Alexandros Alexakis, Yannick Ponty. The Lorentz force effect on the On-Off dynamo intermittency. 2007. ⟨hal-00175646⟩