Resonant cavity modes of a bounded helicon discharge

Five distinct discharge modes are observed in a cylindrically-symmetric hel icon reactor. Each mode is characterized by its plasma impedance, wave mode structure, density distribution and floating potential structure. It is sh own that the lowest two modes are capacitive (E) and inductive (H), while h igher modes are helicon wave (W) modes. Successive wave modes are found to correspond to helicon wave cavity resonances of the plasma-filled vacuum ve ssel, each with a well defined wavevector, density and impedance. Measured wavevectors and densities are in agreement with the helicon wave dispersion relation. The first helicon discharge mode is found to be an m = +/-1 mode , as expected for a double saddle field antenna. Unexpectedly, the second a nd third helicon modes have an m = 0 azimuthal symmetry.