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Article Dans Une Revue New Journal of Physics Année : 2012

Influence of high-permeability discs in an axisymmetric model of the Cadarache dynamo experiment

Résumé

Numerical simulations of the kinematic induction equation are performed on a model configuration of the Cadarache von-Karman-sodium dynamo experiment. The effect of a localized axisymmetric distribution of relative permeability mu(r) that represents soft iron material within the conducting fluid flow is investigated. The critical magnetic Reynolds number Rm(c) for dynamo action of the first non-axisymmetric mode roughly scales like Rm(mu r)(c)-Rm(infinity)(c) proportional to mu(-1/2)(r), i. e. the threshold decreases as mu(r) increases. This scaling law suggests a skin effect mechanism in the soft iron discs. More important with regard to the Cadarache dynamo experiment, we observe a purely toroidal axisymmetric mode localized in the high-permeability discs which becomes dominant for large mu(r). In this limit, the toroidal mode is close to the onset of dynamo action with a (negative) growth rate that is rather independent of the magnetic Reynolds number. We qualitatively explain this effect by paramagnetic pumping at the fluid/disc interface and propose a simplified model that quantitatively reproduces numerical results. The crucial role of the high-permeability discs in the mode selection in the Cadarache dynamo experiment cannot be inferred from computations using idealized pseudo-vacuum boundary conditions (H x n = 0).

Dates et versions

hal-02365516 , version 1 (15-11-2019)

Identifiants

Citer

A Giesecke, Caroline Nore, Frank Stefani, G Gerbeth, Jacques Lã©orat, et al.. Influence of high-permeability discs in an axisymmetric model of the Cadarache dynamo experiment. New Journal of Physics, 2012, 14, pp.053005_1-053005_16. ⟨10.1088/1367-2630/14/5/053005⟩. ⟨hal-02365516⟩
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