Formation of edge pressure pedestal and reversed magnetic shear due to toroidal rotation in a tokamak equilibrium

TL;DR

This paper demonstrates that localized toroidal rotation can induce the formation of an edge pressure pedestal with reversed magnetic shear in tokamak equilibrium, mimicking H-mode conditions through MHD effects.

Contribution

It reveals that strong localized toroidal rotation can directly create pressure pedestals and reversed magnetic shear in tokamaks without additional plasma phenomena.

Findings

Localized toroidal rotation enhances edge current peaking.

Reversal of the safety factor profile occurs due to rotation effects.

Pressure pedestal formation is a natural outcome of MHD equilibrium with rotation.

Abstract

Toroidal rotation is well known to play significant roles in the edge transport and L-H transition dynamics of tokamaks. Our recent calculation finds that a sufficiently strong localized toroidal rotation can directly bring out the formation of edge pressure pedestal with reversed magnetic shear that is reminiscent of an H-mode plasma, purely through the effects of toroidal rotation on the tokamak MHD equilibrium itself. In particular, the enhanced edge toroidal rotation enables a substantial peaking of the parallel current profile near edge in higher $\beta$ regimes, which leads to the flattening or reversal of the local $q$ (safety factor) profile. Here the formation of pressure pedestal along with the reversed magnetic shear region is shown to be the natural outcome of the MHD tokamak equilibrium in a self-consistent response to the presence of a localized toroidal rotation typically observed in H-mode or QH-mode.