Speaker
Dr
Frank Plunian
Description
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 $\tilde{\alpha}$-effect which includes both
usual $\alpha$-effect and turbulent diffusion, plus all
higher order effects. Beyond the onset we find that
$\tilde{\alpha}=O(Rm^{-1})$ 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.
