HR: 09:45h
AN: GP41C-08 [Abstracts]
TI: First Results from the DTS Experiment : the Axi-Symmetric Mean State for a Rotating Spherical Couette
Flow of Sodium with a Strong Imposed Dipolar Magnetic Field
AU: * Nataf, H
EM: nataf@ujf-grenoble.fr
AF: LGIT-CNRS, Maison des Geosciences,
Université Joseph Fourier,
BP 53, Grenoble cedex 9, 38041
France
AU: Alboussière, T
EM: alboussiere@ujf-grenoble.fr
AF: LGIT-CNRS, Maison des Geosciences,
Université Joseph Fourier,
BP 53, Grenoble cedex 9, 38041
France
AU: Brito, D
EM: daniel.brito@ujf-grenoble.fr
AF: LGIT-CNRS, Maison des Geosciences,
Université Joseph Fourier,
BP 53, Grenoble cedex 9, 38041
France
AU: Cardin, P
EM: philippe.cardin@ujf-grenoble.fr
AF: LGIT-CNRS, Maison des Geosciences,
Université Joseph Fourier,
BP 53, Grenoble cedex 9, 38041
France
AU: Gagniere, N
EM: nadege.gagniere@ujf-grenoble.fr
AF: LGIT-CNRS, Maison des Geosciences,
Université Joseph Fourier,
BP 53, Grenoble cedex 9, 38041
France
AU: Schmitt, D
EM: denys.schmitt@ujf-grenoble.fr
AF: LGIT-CNRS, Maison des Geosciences,
Université Joseph Fourier,
BP 53, Grenoble cedex 9, 38041
France
AB:
Little is known about instabilities and turbulence in the magnetostrophic balance, which governs the dynamics of planetary
cores and the generation of their magnetic field. The Derviche Tourneur Sodium (DTS) experiment has been designed to explore
this regime (Cardin et al, Magnetohydrodynamics, 38, 2002). Some 40 liters of liquid sodium fill a spherical shell
between a 7cm-radius copper inner sphere and a 21cm-radius outer shell made of (poorly conducting) stainless steel. Both
spheres can rotate around the vertical axis at different angular velocities between -30 and 30 Hz. The inner sphere encloses
a spherical permanent magnet providing a dipolar field with moment 7 10-5 Tm3.
The magnetic Prandtl number of liquid sodium is 7 10-6. The experiments we have run roughly cover the following range
of dimensionless numbers: magnetic Reynolds number 1 to
20, Ekman number 2 10-7 to 10-6, Rossby number ± 0.2 to ±2, Elsasser number 0.02 to 0.1 (if we use the
intensity of the magnetic field on the outer sphere), and the ratio of Alfvén frequency to rotation frequency varies from
0.02 to 0.1.
Several observational techniques are used to investigate the flow and magnetic field. Torque measurements indicate a strong
coupling between the inner sphere and the sodium, and low
dissipation. We have focused on the axi-symmetric mean state. From electrical potential measurements at the surface of the
sphere, we characterize the azimuthal velocities, which exhibit super-rotation. The induced magnetic field outside the outer
sphere is explained by a meridional circulation, reaching 5-10% of the azimuthal circulation. Profiles of the radial
velocity as a function of radius, obtained by Doppler ultrasonic velocimetry, indicate a rich behavior, including fast
oscillations near the outer boundary.
DE: 1213 Earth's interior: dynamics (1507, 7207, 7208, 8115, 8120)
DE: 1510 Dynamo: theories and simulations
DE: 4490 Turbulence (3379, 4568, 7863)
DE: 5440 Magnetic fields and magnetism
DE: 7524 Magnetic fields
SC: Geomagnetism and Paleomagnetism [GP]
MN: Fall Meeting 2005