Helicon mode formation and radio frequency power deposition in a helicon-produced plasma

Abstract

Time- and space-resolved magnetic (B-dot) probe measurements in combination with measurements of the plasma parameters were carried out to investigate the relationship between the formation and propagation of helicon modes and the radio frequency (rf) power deposition in the core of a helicon plasma. The Poynting flux and the absorbed power density are deduced from the measured rf magnetic field distribution in amplitude and phase. Special attention is devoted to the helicon absorption under linear and nonlinear conditions. The present investigations are attached to recent observations in which the nonlinear nature of the helicon wave absorption has been demonstrated by showing that the strong absorption of helicon waves is correlated with parametric excitation of electrostatic fluctuations.

Travelling Modes in Wave-Heated Plasma Sources

“…The figure also shows the theoretical variation in column length based on (20) and (21). In general, the theoretical curve reproduces the main features of the experiment with large oscillations and sharp minima when the cavity is short and there is a strong interaction between the reflected waves and the travelling waves.…”

“…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.…”

“…An estimate of the magnitude of this effect on wavelength can be made by assuming that the power delivered to the cavity is the difference between the total power P T A and the power delivered to the column which can be estimated from (21). If the volume of a cavity of length l is Al, where A is its cross-sectional area, then the average power density P D is given by…”

Whistler waves with angular momentum in space and laboratory plasmas and their counterparts in free space

“…This wave theory is questionable since in an anisotropic plasma the group and phase velocities differ, which yields different reflections for phase and group velocities. Experimentally, paraxial wave propagation is usually not observed in helicon experiments [118][119][120]. The eigenmode theory does not address how these modes are excited.…”

“…Oblique reflection are different for group and phase velocities [5]. The wave propagation of whistler modes in narrow plasma columns is still poorly understood, leave alone the nonlinear excitation by antennas [118].…”