Wave modelling in a cylindrical non-uniform helicon discharge

TL;DR

This paper presents a RF field solver based on Maxwell's equations and a cold plasma dielectric tensor to model wave phenomena in a non-uniform helicon discharge, matching experimental measurements with adjusted parameters.

Contribution

The study introduces a wave modeling approach that accounts for non-uniform plasma density and magnetic fields in a helicon discharge, improving agreement with experimental data.

Findings

The solver's profiles match measurements when adjusted for collision frequency and antenna radius.

Ion-acoustic turbulence may explain the need for increased collision frequency in simulations.

Adjusting antenna radius helps overcome mode limitations in the RF solver.

Abstract

A radio frequency (RF) field solver based on Maxwell's equations and a cold plasma dielectric tensor is em- ployed to describe wave phenomena observed in a cylindrical non-uniform helicon discharge. The experiment is carried out on a recently built linear plasma-material interaction machine: the MAGnetized Plasma In- teraction Experiment (MAGPIE) [B. D. Blackwell, J. F. Caneses, C. Samuell, J. Wach, J. Howard, and C. S. Corr, submitted on 25 March 2012 to Plasma Sources Science and Technology], in which both plasma density and static magnetic field are functions of axial position. The field strength increases by a factor of 15 from source to target plate, and plasma density and electron temperature are radially non-uniform. With an enhancement factor of 9.5 to the electron-ion Coulomb collision frequency, 12% reduction in the antenna radius, and the same other conditions as employed in the experiment, the solver produces axial and radial profiles of wave amplitude and phase that are consistent with measurements. Ion-acoustic turbulence, which can happen if electron drift velocity exceeds the speed of sound in magnetized plasmas, may account for the factor of 9.5 used to match simulated results with experimental data. To overcome the single m vacuum solu- tion limitations of the RF solver, which can only compute the glass response to the same mode number of the antenna, we have adjusted the antenna radius to match the wave field strength in the plasma.(not finished because of the limited number of characters, please see the full paper)