Preference of Right-Handed Whistler Modes and Helicon Discharge Directionality due to Plasma Density Gradients

TL;DR

This paper investigates how plasma density gradients influence the directionality and polarization preference of whistler and helicon waves in magnetized plasmas, revealing new insights into wave behavior and discharge control.

Contribution

It demonstrates that radial density gradients are essential for explaining the preference for right-handed whistlers and the reversal of discharge direction in helicon plasmas, supported by simulations.

Findings

Radial density gradients are crucial for wave behavior.

Discharge direction can be reversed by changing antenna helicity or magnetic field.

Simulations confirm the role of density gradients in wave preference.

Abstract

Whistlers are magnetized plasma waves in planetary magnetospheres. Bounded whistlers, known as helicons, can create high-density laboratory plasmas. We demonstrate reversal of the plasma discharge direction by changing either antenna helicity or magnetic field direction. Simulations reproduce these findings only in the presence of a radial density gradient. Inclusion of such a gradient in the wave equation gives rise to azimuthal shear currents which for the first time consistently explains the preference of right- over left-handed whistlers and the discharge directionality in helicon plasmas.