Axial propagation of helicon waves

Traveling‐ and standing‐wave characteristics of the wave fields have been measured in a helicon discharge using a five‐turn, balanced magnetic probe movable along the discharge axis z. Helical and plane‐polarized antennas were used, and the magnitude and direction of the static magnetic field were varied, yielding three primary results. (1) As the density varies along z, the local wavelength agrees with the local dispersion relation. (2) Beats in the z variation of the wave intensity do not indicate standing waves, but instead are caused by the simultaneous excitation of two radial eigenmodes. Quantitative agreement with theory is obtained. (3) The damping rate of the helicon wave is consistent with theoretical predictions based on collisions alone.