Nonlinear Helicons ---an analytical solution elucidating multi-scale structure

TL;DR

This paper presents an analytical solution for nonlinear helicon waves in plasma, revealing their multi-scale structure through the combination of dispersive effects and nonlinearity, with implications for understanding plasma wave behavior.

Contribution

It introduces an exact nonlinear solution in extended MHD that combines helicon and Trivelpiece-Gould waves, highlighting multi-scale properties and mode interactions.

Findings

The solution combines helicon and TG waves in certain regimes.

Energy partition depends on wave field helicities.

Different mode combinations occur at varying plasma parameters.

Abstract

The helicon waves exhibit varying characters depending on plasma parameters, geometry, and wave numbers. Here we elucidate an intrinsic multi-scale property embodied by the combination of dispersive effect and nonlinearity. The extended magnetohydrodynamics model (exMHD) is capable of describing wide range of parameter space. By using the underlying Hamiltonian structure of exMHD, we construct an exact nonlinear solution which turns out to be a combination of two distinct modes, the helicon and Trivelpiece-Gould (TG) waves. In the regime of relatively low frequency or high density, however, the combination is made of the TG mode and an ion cyclotron wave (slow wave). The energy partition between these modes is determined by the helicities carried by the wave fields.