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Helicon waves in a plasma confined by a cylinder are treated. The undamped normal modes of the helicon (H) and Trivelpiece-Gould (TG) waves have distinctly different wave patterns at high magnetic fields but at low fields have similar patterns and therefore interact strongly. Damping of these modes, their excitation by antennas, and the RF plasma absorption efficiency are considered. Nonuniform plasmas are treated by solving a fourth order ordinary differential equation numerically. A significant difference between this and earlier codes which divide the plasma into uniform shells is made clear. Excitation of the weakly damped H wave, followed by conversion to the strongly damped TG wave which leads to high helicon discharge efficiency, is examined for realistic density profiles. A reason for the greater heating efficiency of the m = +1 versus the m = -1 mode for axially peaked profiles is provided.

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Helicon waves are waves in low-temperature, partially ionized plasmas in a dc magnetic field (B-field). The study of helicons involves both ion-neutral collisions and Larmor orbits, even when the B-field is uniform. Helicon discharges are ionized by helicon waves generated by a radiofrequency (RF) antenna. Interest in helicon discharges arose because of the high plasma densities they generate compared with other RF sources at comparable powers. The semiconductor industry has not taken advantage of this, even since the possible use of permanent magnets for the B-field has been demonstrated. Nonetheless, a large literature on helicons has evolved because of the numerous problems these discharges posed and the interesting physics found in their solutions.

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The theory of helicon waves is extended to include finite electron mass. This introduces an additional branch to the dispersion relation that is essentially an electron cyclotron or Trivelpiece–Gould (TG) wave with a short radial wavelength. The effect of the TG wave is expected to be important only for low dc magnetic fields and long parallel wavelengths. The normal modes at low fields are mixtures of the TG wave and the usual helicon wave and depend on the nature of the boundaries. Computations show, however, that since the TG waves are damped near the surface of the plasma, the helicon wave at high fields is almost exactly the same as is found when the electron mass is neglected.

Components of the wave magnetic field in a helicon discharge have been measured with a single-turn, coaxial magnetic probe. Left- and right-handed helical antennas, as well as plane-polarized antennas, were used; and the results were compared with the field patterns computed for a nonuniform plasma. The results show that the right-hand circularly polarized mode is preferentially excited with all antennas, even those designed to excite the left-hand mode. For right-hand excitation, the radial amplitude profiles are in excellent agreement with computations.

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.