Large-scale fluctuations and dynamics of the Bullard-von Karman dynamo

Gautier Verhille (1) , Nicolas Plihon (1) , Gregory Fanjat (1) , Romain Volk (1) , Mickaël Bourgoin (2) , Jean-François Pinton (1)

1 Phys-ENS - Laboratoire de Physique de l'ENS Lyon
2 LEGI - Laboratoire des Écoulements Géophysiques et Industriels [Grenoble]

A synthetic fluid dynamo built in the spirit of the Bullard device (Bullard, The stability of a homopolar dynamo, Proc. Camb. Phil. Soc. 1955, 51, 744) is investigated. It is a two-step dynamo in which one process stems from the fluid turbulence, while the other part is achieved by a linear amplification of currents in external coils (Bourgoin et al., A bullard-von Karman dynamo, New J. Phys., 2006, 8, 329). Modifications in the forcing are introduced in order to change the dynamics of the flow, and hence the dynamo behavior. Some features, such as on-off intermittency at onset of dynamo action, are very robust. Large-scale fluctuations have a significant impact on the resulting dynamo, in particular in the observation of magnetic field reversals.

Mots clés: Magnetohydrodynamics; Dynamo; Bifurcation; Turbulence; On-off intermittency

Domaines: Mécanique des fluides [physics.class-ph]; Mécanique des fluides [physics.class-ph]; Géophysique [physics.geo-ph]

Gautier Verhille, Nicolas Plihon, Gregory Fanjat, Romain Volk, Mickaël Bourgoin, et al.. Large-scale fluctuations and dynamics of the Bullard-von Karman dynamo. Geophysical and Astrophysical Fluid Dynamics, 2010, 104 (2-3), pp.189-205. ⟨10.1080/03091920903301938⟩. ⟨hal-00492233⟩