A dynamo effect of multiple tearing modes on Taylor relaxation

Abstract

The dynamo effect of multiple tearing modes in a force-free plasma is investigated using resistive magnetohydrodynamics equations. In a steady state, two tearing modes are considered. It is found that the dynamo effect is related to the distance between the two rational surfaces and the magnetic island width. The lambda = j . B / | B | (2) profile is flatter for closer rational surfaces and wider magnetic islands. The case of an arbitrary number of tearing modes is also considered, and it is found that the lambda profile in a finite plasma region can be flattened by the dynamo effect if there are enough tearing modes. This indicates that lambda can be flattened in the entire plasma region, which makes it clear that the dynamo effect actually flattens lambda rather than the current density. In the growth stage, the case of a growing tearing mode and two saturated modes is considered. The calculation shows that the middle tearing mode makes connections between the two modes on each side, playing the role of a mediator. Our results provide a more clear explanation for the dynamo effect of multiple tearing modes as a possible mechanism behind the Taylor relaxation process. Published under an exclusive license by AIP Publishing