DISCHARGE EQUILIBRIUM OF A HELICON PLASMA

The axial dependence of the plasma density, electron temperature, plas ma potentials, and the 488 nm argon ion emission intensity have been m easured in argon helicon discharges excited by both right helical and Nagoya III antennas for various magnitudes and directions of the magne tic 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 azimutha l mode when B is parallel (parallel to) to the propagation vector k, a nd the m = -1 mode when B is antiparallel (#) to k. The plasma is foun d to be more dense in the former case (B parallel to k, m = +1), and t he density peaks several antenna lengths downstream in the k direction . Nagoya III antennas are symmetric antennas that should excite the sa me azimuthal mode content in either magnetic field direction; indeed, the light profile was found to be independent of field direction. In t he near field, under the antennas, the density is approximately the sa me for both antenna geometries and magnetic field directions. These re sults indicate that the m = +1 mode is preferentially excited regardle ss of the antenna helicity.