Discharge equilibrium of a helicon plasma

Abstract

The axial dependence of the plasma density, electron temperature, plasma potentials, and the 488 nm argon ion emission intensity have been measured in argon helicon discharges excited by both right helical and Nagoya III antennas for various magnitudes and directions of the magnetic field B. The plasma parameters were monitored with RF-compensated probes, while the emission line was detected with an optical emission spectrometer that incorporates an optical fibre and a miniature lens. The right helical antennas were designed to excite the m = +1 azimuthal mode when B is parallel () to the propagation vector k, and the m = −1 mode when B is antiparallel (#) to k. The plasma is found to be more dense in the former case (B k, m = +1), and the density peaks several antenna lengths downstream in the k direction. Nagoya III antennas are symmetric antennas that should excite the same azimuthal mode content in either magnetic field direction; indeed, the light profile was found to be independent of field direction. In the near field, under the antennas, the density is approximately the same for both antenna geometries and magnetic field directions. These results indicate that the m = +1 mode is preferentially excited regardless of the antenna helicity.

Two-dimensional imaging of a helicon discharge

“…Because of the higher threshold for direct excitation from Ar I, one would expect this process to be negligible. Indeed, in a previous paper Sudit and Chen [18] showed that data on the axial variation of 488 nm light agreed with calculations, based on measured T e values, assuming the n 2 dependence of the Ar II process but not with the n dependence of the Ar I process. Thus, the light intensity in our CCD images should be proportional to n 2 σ ν .…”

Wave propagation and absorption simulations for helicon sources

“…Recent experimental observations 5,[21][22][23] show that the plasma density for helicon plasma sources often peaks several wavelengths downstream from the antenna, and its axial variation can substantially affect the electromagnetic wave field profiles and power absorption of the plasma electrons. It is, therefore, necessary to develop a two-dimensional (r,z) model to account for the effects of the axial variation of the plasma density, temperature, and applied magnetic field on helicon wave propagation and absorption.…”

Azimuthally symmetric pseudosurface and helicon wave propagation in an inductively coupled plasma at low magnetic field

“…A mode transition is also observed in helicon plasma sources, which show a three-step mode transition, that is from E mode to H mode and finally to helicon mode. 5 Smullin et al 6 recognized that when the phase velocity of an electromagnetic wave in a rectangular metallic wave guide filled with plasma with constant B field satisfies v ph (ϭ /k)Ӷc, the wave can be treated by the electrostatic approximation. The existence of this mode was observed independently by Trivelpiece and Gould.…”