Diamagnetic pumping near the base of a stellar convection zone

TL;DR

This paper investigates how inhomogeneous turbulence causes diamagnetic pumping that can confine magnetic fields in stellar interiors, influencing the formation of the solar tachocline and magnetic structures in stars.

Contribution

It demonstrates the role of diamagnetic pumping in magnetic field confinement near the base of stellar convection zones and establishes conditions for its efficiency based on diffusivity ratios.

Findings

Diamagnetic pumping can confine magnetic fields in stellar radiative cores.

Efficient confinement requires a diffusivity ratio greater than 10^5.

Persistent magnetic structures in young stars suggest absence of tachoclines.

Abstract

The property of inhomogeneous turbulence in conducting fluids to expel large-scale magnetic fields in the direction of decreasing turbulence intensity is shown as important for the magnetic field dynamics near the base of a stellar convection zone. The downward diamagnetic pumping confines a fossil internal magnetic field in the radiative core so that the field geometry is appropriate for formation of the solar tachocline. For the stars of solar age, the diamagnetic confinement is efficient only if the ratio of turbulent magnetic diffusivity of the convection zone to the (microscopic or turbulent) diffusivity of the radiative interiour is larger than 10^5. Confinement in younger stars require still larger diffusivity ratio. The observation of persistent magnetic structures on young solar-type stars can thus provide evidences for the nonexistence of tachoclines in stellar interiors and on the level of turbulence in radiative cores.