Characterization of the resonant electromagnetic mode in helicon discharges

Abstract

This paper presents experimental evidence for the existence of a resonant electromagnetic mode in a helicon plasma, and characterizes its resonant frequency, energy absorption rate, and contribution to the overall power balance. An experimental method developed to detect and characterize the plasma impedance is introduced. Power flow analysis shows that the resonant electromagnetic mode is the dominant mechanism driving helicon plasma discharges in cylindrical geometry. The weakly damped wavefields are absorbed in a short distance, indicating that the wavefields may be trapped in a potential well created by a density gradient.

Measurements and modeling of radio frequency field structures in a helicon plasma

“…As a result, the frequency of this wave is consistent with the discharge operational frequency. 7 There have been two recent experimental works 8,9 aimed at determining whether the waves excited by the helicon antenna are RLH waves and at understanding the role of RLH waves in the global power balance. Both experiments were performed on the same device.…”

Travelling Modes in Wave-Heated Plasma Sources

“…To test this scaling function for α/β, a number of papers that include data on the decay of helicon waves have been consulted to determine experimental values for α/β, in terms of the parameters χ/a, ω, and n 0 [10], [11], [16]- [26]. In some cases, explicit values of the parameters are not reported but have been inferred from the relevant graphs.…”

“…In some cases, explicit values of the parameters are not reported but have been inferred from the relevant graphs. The papers investigate a wide variety of processes to explain the absorption mechanisms in different regimes, including electron trapping in the axial electric field of traveling waves [10], electron-neutral and electron-ion collisions [16], [17], collisionless Landau damping [9, p. 442], resonance absorption through wave trapping by density gradients [11], and parametric instabilities leading to ion-sound and Trivelpiece-Gould waves [21]- [23]. Rather than attempting to deal with each of these mechanisms in detail, for the purposes of (41), a single effective collision frequency ν eff = 3 × 10 8 s −1 has been selected to give the best overall match.…”

“…It should be noted that η is not the same as the antenna impedance Z A "seen" by the matching network as Z A also includes the resistance and reactance of the antenna itself, plus the plasma impedance reflected back into the antenna by, for example, transformer action in the case of the helicon discharge [11]. This impedance may include not only the wave impedance but also the inductive reactance of the secondary of the transformer [11].…”

“…This impedance may include not only the wave impedance but also the inductive reactance of the secondary of the transformer [11]. Fig.…”