Mode conversion in cold low-density plasma with a sheared magnetic field

TL;DR

This paper develops a new theory for electromagnetic mode conversion in cold, low-density plasmas with strong magnetic shear, addressing limitations of classic models and aiding fusion plasma research.

Contribution

It introduces a novel approach to describe mode conversion without narrow resonance assumptions, applicable to fusion and stellarator plasma edge modeling.

Findings

A new method for preparing wave modes in high-density plasma.

The theory extends beyond classic Landau--Zener approximations.

Potential applications in fusion plasma wave-power input modeling.

Abstract

A theory is proposed that describes mutual conversion of two electromagnetic modes in cold low-density plasma, specifically, in the high-frequency limit where the ion response is negligible. In contrast to the classic (Landau--Zener-type) theory of mode conversion, the region of resonant coupling in low-density plasma is not necessarily narrow, so the coupling matrix cannot be approximated with its first-order Taylor expansion; also, the initial conditions are set up differently. For the case of strong magnetic shear, a simple method is identified for preparing a two-mode wave such that it transforms into a single-mode wave upon entering high-density plasma. The theory can be used for reduced modeling of wave-power input in fusion plasmas. In particular, applications are envisioned in stellarator research, where the mutual conversion of two electromagnetic modes near the plasma edge is a known issue.