Parametric instability of the helical dynamo

University of Grenoble, Grenoble, Rhône-Alpes, France
Physics of Fluids (Impact Factor: 2.03). 05/2007; 19(5):054109. DOI: 10.1063/1.2734118
Source: arXiv


We study the dynamo threshold of a helical flow made of a mean (stationary) plus a fluctuating part. Two flow geometries are studied, either (i) solid body or (ii) smooth. Two well-known resonant dynamo conditions, elaborated for stationary helical flows in the limit of large magnetic Reynolds numbers, are tested against lower magnetic Reynolds numbers and for fluctuating flows (zero mean). For a flow made of a mean plus a fluctuating part the dynamo threshold depends on the frequency and the strength of the fluctuation. The resonant dynamo conditions applied on the fluctuating (resp. mean) part seems to be a good diagnostic to predict the existence of a dynamo threshold when the fluctuation level is high (resp. low). Comment: 37 pages, 8 figures

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Available from: Franck Plunian, Nov 01, 2012
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    • "Recent work on the cylindrical Ponomarenko dynamo shows that magnetic growth persists when the amplitudes of the helical flow has a small time-dependent (fluctuating) part. Dynamo action even can occur when the meridional and azimuthal fluctuations are slightly different functions of time, forcing the resonant curve to also change with time (Peyrot et al. 2007, 2008). Similar behaviour undoubtedly carries over to the spherical single roll dynamos we consider. "
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