The ion acoustic instability of the rotating cylindrical helicon discharge plasma

TL;DR

This paper develops a kinetic theory for cylindrical helicon plasmas, revealing how azimuthal electron rotation and inhomogeneities lead to ion acoustic instability localized in regions with strong electric field and density gradients.

Contribution

It introduces a comprehensive kinetic model accounting for cylindrical geometry and inhomogeneity, explaining the origin of ion acoustic instability in helicon plasmas.

Findings

Azimuthal electron rotation caused by radial electric field inhomogeneity.

Ion acoustic instability localized in regions with strong electric field and density gradients.

Instability exceeds parametric instabilities driven by electron oscillations.

Abstract

The kinetic theory for the cylindrical plasma, produced by the cylindrically symmetric (azimuthal mode number m=0) helicon wave, is developed with accounting for the cylindrical geometry and the radial inhomogeneity of the helicon wave and plasma. This theory reveals macroscale effect of the azimuthal steady rotation of electrons with a radially inhomogeneous angular velocity, caused by radial inhomogeneity of the helicon electric field. It is found that this sheared rotation as well as the electron density and temperature inhomogeneity are responsible for the development of the high frequency ion acoustic instability of the inhomogeneous cylindrical plasma. This instability is spatially localized in the region of strong gradients of the helicon wave electric field and of the plasma density, where it is more stronger than the parametric instabilities driven by the oscillating motion of the electrons relative to ions in the helicon wave.