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Etude expérimentale du régime magnétostrophique avec DTS (Derviche Tourneur Sodium)

Abstract : The DTS (Derviche Tourneur Sodium) experiment has been constructed in order to explore the magnetostrophic regime expected for planetary cores, in which the Coriolis and Lorentz forces are in balance. Two concentric spheres are differentially rotating, and the spherical shell is filled with liquid sodium. A dipolar magnetic field is imposed thanks to permanent magnets inside the inner sphere. This magnetohydrodynamical spherical Couette flow is studied with different measurements : velocity (Doppler), electric potential and induced magnetic field.
Angular velocity profiles reveal different regions in the spherical shell : super-rotation is present near the inner sphere, then the angular velocity is nearly constant and decreases towards the outer sphere. The similar shape of angular velocity profiles in the geostrophic region is explained with a model based on a modified Taylor's state, in which the turbulent friction in Ekman layers is considered. In the volume, the level of turbulence is low, and the observed fluctuations are attributed to waves.
The scattering for a given forcing could be due to variations in the electric coupling between liquid sodium and the copper inner sphere. Using the electric potential difference as a proxy of the flow velocity, we identify a particular regime from the induced magnetic field measurements. Large amplitudes are obtained for counter-rotating spheres. We suggest that dynamo action might be favored in such a situation.
Recent experiments with a good electric coupling yield stable and impressive measurements. Moreover, new induced magnetic field measurements along a meridian and inside the spherical shell give us new constraints.
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https://tel.archives-ouvertes.fr/tel-00377661
Contributor : Nadège Gagniere <>
Submitted on : Wednesday, April 22, 2009 - 4:17:49 PM
Last modification on : Thursday, November 19, 2020 - 3:54:28 PM
Long-term archiving on: : Thursday, June 10, 2010 - 9:29:35 PM

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Nadège Gagnière. Etude expérimentale du régime magnétostrophique avec DTS (Derviche Tourneur Sodium). Sciences de la Terre. Université Joseph-Fourier - Grenoble I, 2009. Français. ⟨tel-00377661⟩

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