Transient Regimes of the Screw Dynamo

Abstract

The screw dynamo is a critical phenomenon—a self-excitation that occurs only when the magnetic Reynolds number (Rm) reaches some threshold value. Temporal magnetic field growth is shown to occur at Rm slightly smaller than this critical value. The appearance of temporal growth is also limited from below by the second critical value of Rm. If, however, a seed magnetic field is present permanently, and not just at the initial time of evolution, temporal subcritical magnetic field growth gives rise to a stationary magnetic configuration. This stationary magnetic field turns out to be particularly strong if the seed field in the form of a traveling wave coincides in phase velocity with the magnetic field that emerges in the presence of a self-excitation. The possibilities for detecting such a resonance in the subcritical regime of operation of an experimental setup based on the screw dynamo are considered.