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Dynamo generated by the centrifugal instability

Abstract : We present a scenario for magnetic field amplification where an electrically conducting fluid is confined in a differentially rotating, spherical shell with thin aspect ratio. When the angular momentum sufficiently decreases outwards, a hydrodynamic instability develops in the equatorial region, characterized by pairs of counter-rotating toroidal vortices similar to those observed in cylindrical Couette flow. These spherical Taylor-Couette vortices generate a subcritical dynamo magnetic field dominated by nonaxisymmetric components. We show that the critical magnetic Reynolds number seems to reach a constant value at large Reynolds number and that the global rotation can strongly decrease the dynamo onset. Our numerical results are understood within the framework of a simple dynamical system, and we propose a low-dimensional model for subcritical dynamo bifurcations. Implications for both laboratory dynamos and astrophysical magnetic fields are finally discussed.
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Submitted on : Saturday, February 19, 2022 - 12:44:35 PM
Last modification on : Thursday, March 17, 2022 - 10:08:43 AM

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Florence Marcotte, Christophe Gissinger. Dynamo generated by the centrifugal instability. Physical Review Fluids, 2016, 1, pp. 438-441. ⟨10.1103/PhysRevFluids.1.063602⟩. ⟨insu-03581276⟩

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