Helicon plasma in a magnetic shuttle

TL;DR

This paper models helicon plasma within a magnetic shuttle formed by tandem magnetic mirrors, analyzing wave structures, power absorption, and the effects of various parameters, revealing key behaviors of helicon modes in such configurations.

Contribution

It introduces the concept of a magnetic shuttle for helicon plasma confinement and provides detailed electromagnetic modeling and analysis of wave behavior in this setup.

Findings

Wave magnitude and power absorption decrease with higher frequency and lower field strength.

Maximum power absorption occurs at a certain plasma density level.

Radial wave structures remain consistent, with axial standing waves due to interference.

Abstract

The definition of magnetic shuttle is introduced to describe the magnetic space enclosed by two tandem magnetic mirrors with the same field direction and high mirror ratio. Helicon plasma immersed in such a magnetic shuttle which can provide the confinement of charged particles is modeled using an electromagnetic solver. The perpendicular structure of wave field along this shuttle is given in terms of stream vector plots, showing significant change from midplane to ending throats, and the vector field rotates and forms a circular layer that separating plasma column radially into core and edge regions near the throats. The influences of driving frequency, plasma density and field strength on the wave field and power absorption are computed in detail. It is found that the wave magnitude and power absorption decrease for increased driving frequency and reduced field strength, and maximize around a certain level of plasma density. The axial standing-wave feature always exists, due to the interference between forward and reflected waves from ending magnetic mirrors, while the radial wave field structure largely stays the same. Distributions of wave energy density and power absorption density all show shrinking feature from midplane to ending throats, which is consistent with the nature of helicon mode that propagating along field lines. Theoretical analysis based on a simple magnetic shuttle and the governing equation of helicon waves shows consistency with computed results and previous studies.