A flowing plasma model to describe drift waves in a cylindrical helicon discharge

TL;DR

This paper applies a two-fluid plasma model to interpret drift wave oscillations in a cylindrical helicon discharge, showing qualitative agreement with experimental data and identifying key parameters influencing wave behavior.

Contribution

It extends a two-fluid model originally for centrifuge plasmas to describe drift waves in a helicon discharge, providing new insights into plasma oscillations in this context.

Findings

Model predicts wave frequencies consistent with measurements.

Density perturbation profiles match experimental data.

Oscillation frequency depends on electron temperature and magnetic field.

Abstract

A two-fluid model developed originally to describe wave oscillations in the vacuum arc centrifuge, a cylindrical, rapidly rotating, low temperature and confined plasma column, is applied to interpret plasma oscillations in a RF generated linear magnetised plasma (WOMBAT), with similar density and field strength. Compared to typical centrifuge plasmas, WOMBAT plasmas have slower normalised rotation frequency, lower temperature and lower axial velocity. Despite these differences, the two-fluid model provides a consistent description of the WOMBAT plasma configuration and yields qualitative agreement between measured and predicted wave oscillation frequencies with axial field strength. In addition, the radial profile of the density perturbation predicted by this model is consistent with the data. Parameter scans show that the dispersion curve is sensitive to the axial field strength and the electron temperature, and the dependence of oscillation frequency with electron temperature matches the experiment. These results consolidate earlier claims that the density and floating potential oscillations are a resistive drift mode, driven by the density gradient. To our knowledge, this is the first detailed physics model of flowing plasmas in the diffusion region away from the RF source. Possible extensions to the model, including temperature non-uniformity and magnetic field oscillations, are also discussed.