Magnetic topology and current channels in plasmas with toroidal current density inversions

TL;DR

This paper analyzes the magnetic field structure in axisymmetric plasmas with current density inversions, revealing stable non-nested magnetic surfaces and current channels with specific topological properties.

Contribution

It provides a general expression relating positive and negative currents and derives an analytical solution consistent with experimental measurements.

Findings

Positive current channels are about twice as strong as the central negative current.

The magnetic surfaces are non-nested and structurally stable.

The analytical solution aligns with observed magnetic pitch measurements.

Abstract

The equilibrium magnetic field inside axisymmetric plasmas with inversions on the toroidal current density is studied. Structurally stable non-nested magnetic surfaces are considered. For any inversion in the internal current density the magnetic families define several positive current channels about a central negative one. A general expression relating the positive and negative currents is derived in terms of a topological anisotropy parameter. Next, an analytical local solution for the poloidal magnetic flux is derived and shown compatible with current hollow magnetic pitch measurements shown in the literature. Finally, the analytical solution exhibits non-nested magnetic families with positive anisotropy, indicating that the current inside the positive channels have at least twice the magnitude of the central one.