Large-scale dynamo action of magnetized Taylor–Couette flows. Issue 1 (3rd February 2020)

• Record Type: Journal Article
• Authors: Rüdiger, G; Schultz, M
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 493:Issue 1(2020)
• Page Start: 1249
• Page End: 1260
• Publication Date: 2020-02-03
• Subjects: dynamo -- instabilities -- MHD -- magnetic fields; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/staa293
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: A conducting Taylor–Couette flow with quasi-Keplerian rotation law containing a toroidal magnetic field serves as a mean-field dynamo model of the Tayler–Spruit type. The flows are unstable against non-axisymmetric perturbations which form electromotive forces defining α effect and eddy diffusivity. If both degenerated modes with m = ±1 are excited with the same power then the global α effect vanishes and a dynamo cannot work. It is shown, however, that the Tayler instability produces finite α effects if only an isolated mode is considered but this intrinsic helicity of the single-mode is too low for an α 2 dynamo. Moreover, an α Ω dynamo model with quasi-Keplerian rotation requires a minimum magnetic Reynolds number of rotation of Rm ≃ 2000 to work. Whether it really works depends on assumptions about the turbulence energy. For a steeper-than-quadratic dependence of the turbulence intensity on the magnetic field, however, dynamos are only excited if the resulting magnetic eddy diffusivity approximates its microscopic value, ηT ≃ η. By basically lower or larger eddy diffusivities the dynamo instability is suppressed.