Amplification of whistler waves in a thin Keplerian disc embedded in an axisymmetric magnetic field

TL;DR

This paper investigates how whistler waves can be amplified in thin Keplerian discs with magnetic fields, revealing conditions under which these waves grow due to density and magnetic effects, with implications for disc stability.

Contribution

It demonstrates that whistler waves are amplified in Keplerian discs with combined density stratification and poloidal magnetic fields, considering the strong Hall effect limit.

Findings

Whistler waves are amplified along their trajectory.

Keplerian discs can be destabilized by combined density and magnetic effects.

Other wave modes do not experience amplitude change.

Abstract

The linear stability of thin Keplerian discs of weakly ionized polytropic plasma embedded in a mixed (toroidal-poloidal) axisymmetric magnetic field is studied. The effects of the central body on the equilibrium state of the discs are modeled by an axial total current and a dipole magnetic field. Studying the amplification of high-frequency waves shows that Keplerian discs can be destabilized due to combined effects of equilibrium density stratification and poloidal magnetic field. By considering a boundary value problem in the limit of strong Hall effect, it is shown that whistler waves which are free of direct influence of compressibility, rotation and gravity, are amplified along their trajectory while other modes of wave propagation do not change their amplitude.