Characterisation of density linear control in a helicon plasma source with tunable antenna wavenumber spectra

Abstract The helicon plasma source is widely used in various fields due to its high ionisation rate. The helicon wave dispersion relationship indicates that the density is proportional to axial wavenumbers. In this study, we systematically investigated how the plasma density varies with the axial wavenumber by employing several phased antenna systems. The antenna comprised different numbers of loops, and each loop was connected to an individual radio frequency power source. We adjusted the plasma density from approximately 10 11 to 10 13 cm −3 . Such two orders of magnitude adjustments may provide a novel operation mode for helicon applications. The density was linearly proportional to the axial wavenumber, when the axial wavenumber was not exceptionally large. In addition, in a low magnetic field, density peaks were observed in all three antenna configurations. The density peak appears irrespective of whether the Landau damping frequency is higher than collision frequency. This finding suggested that Landau damping and other mechanisms can lead to such a phenomenon of low field density peak.