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.

Observation of low-frequency oscillation in argon helicon discharge

“…The frequency varies between 22 Hz and 86 Hz, when magnetic field B increases from 0 to 110 G at power P RF =300 W. It is noticed that there is a peak of frequency around B=80 G, which is similar to that in electron density (see figure 3), corresponding to the low density peak [39][40][41][42][43][44].…”

“…From figure 3(b), the relative oscillation amplitude of the density (defined as Δn e /n e,max ) decreases from 93% to 21% with increasing B. A peak (Δn e /n e,max ∼37%) is achieved around B=80 G, which is similar to the low field peak [39][40][41][42][43][44]. The relative oscillation amplitude of temperature (defined as ΔT e /T e,min ) decreases with the magnetic field, ranging from 98% to 6% in B=0-50 G, and stays constant of ΔT e /T e,min =6% at B>60 G. Both relative amplitudes show two stages at increasing magnetic field, large amplitude oscillation with relative amplitude more than 90% in B=0-50 G and small amplitude oscillation with relative amplitude less than 40% in B=60-110 G. Considering the difference in typical density of the CCP and ICP modes, the density at the turning point (around B=60 G) is about 1×10 11 cm −3 , which is the critical value for achieving ICP or transition from CCP to ICP.…”

Particle simulations on propagation and resonance of lower hybrid wave launched by phased array antenna in linear devices

“…However, to couple tremendous external energy into the plasmas under various conditions with high efficiency, it is important to understand wave coupling and plasma response. Although loop antenna sources with a tunable antenna wavenumber spectrum have been successfully achieved in the ion cyclotron range of frequency and a helicon plasma experiment [19,20], the tunable phased array antenna has not been investigated in lower hybrid resonance heating (LHRH), in particular at simulation.…”