Transition from large-scale to small-scale dynamo

Abstract

The dynamo equations are solved numerically with a helical forcing corresponding to the Roberts flow. In the fully turbulent regime the flow behaves as a Roberts flow on long time scales, plus turbulent fluctuations at short time scales. The dynamo onset is controlled by the long time scales of the flow, in agreement with the former Karlsruhe experimental results. The dynamo mechanism is governed by a generalized $\alpha$-effect which includes both usual $\alpha$-effect and turbulent diffusion, plus all higher order effects. Beyond the onset we find that this generalized $\alpha$-effect scales as $O(R{m}^{-1})$ suggesting the take-over of small-scale dynamo action. This is confirmed by simulations in which dynamo occurs even if the large-scale field is artificially suppressed.

4 pages, 3 figures

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Cited by in corpus (12)

• Dynamo theories
• Shell Models of Magnetohydrodynamic Turbulence
• Searching for the fastest dynamo: Laminar ABC flows
• Energy transfers in dynamos with small magnetic Prandtl numbers
• Amplification of large-scale magnetic field in nonhelical magnetohydrodynamics
• Dynamo enhancement and mode selection triggered by high magnetic permeability
• The fate of alpha dynamos at large $Rm$
• Kinematic dynamo action in square and hexagonal patterns
• Structures and Lagrangian statistics of the Taylor-Green Dynamo
• Transition to turbulent dynamo saturation
• The onset of turbulent rotating dynamos at the low $Pm$ limit
• Dynamo saturation down to vanishing viscosity: strong-field and inertial scaling regimes