Effect of the Lorentz force on on-off dynamo intermittency
A. Alexakis and Y. Ponty

Saturday 27 November 2010 by Ponty Yannick

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 countereffect of the Lorentz
force in the nonlinear 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 bursts -on phases- are observed
than 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.

 Alexakis, A. and Ponty, Y., "Effect of the Lorentz force on on-off dynamo intermittency", Physical Review E, 77, p. 56308 ( (2008) (doi:10.1103/PhysRevE.77.056308)



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