Fast dynamos in spherical boundary-driven flows

TL;DR

This paper demonstrates the feasibility of fast dynamos in spherical boundary-driven flows through numerical simulations of realistic, self-consistently determined flows, showing magnetic field self-excitation over a range of parameters.

Contribution

It introduces a new approach by considering realistic, boundary-driven flows from the Navier-Stokes equation for fast dynamo studies.

Findings

Magnetic fields are self-excited in the simulated flows.

Growth rates are independent of magnetic Reynolds number at large Rm.

The study confirms the possibility of fast dynamos in spherical boundary-driven flows.

Abstract

We numerically demonstrate the feasibility of kinematic fast dynamos for a class of time-periodic axisymmetric flows of conducting fluid confined inside a sphere. The novelty of our work is in considering the realistic flows, which are self-consistently determined from the Navier-Stokes equation with specified boundary driving. Such flows can be achieved in a new plasma experiment, whose spherical boundary is capable of differential driving of plasma flows in the azimuthal direction. We show that magnetic fields are self-excited over a range of flow parameters such as amplitude and frequency of flow oscillations, fluid Reynolds (Re) and magnetic Reynolds (Rm) numbers. In the limit of large Rm, the growth rates of the excited magnetic fields are of the order of the advective time scales and practically independent of Rm, which is an indication of the fast dynamo.