We consider the excitation and absorption of waves in a plasma cavity with parameters typical for helicon sources. rf power is shown to be transferred into the plasma via two channels. The first is realized by weakly damping helicon waves which are excited directly by the azimuthal parts of the antenna and penetrate into the bulk plasma. Electrostatic waves arising at a plasma edge owing to the linear mode conversion form the second channel. Strongly damped electrostatic waves can reach a plasma core at low magnetic fields only, while at high fields they deposit energy at the periphery of the plasma column. A principal fraction of the rf power is transferred into the plasma via the electrostatic channel, and so the power input turns out to be volume at low magnetic fields and surface at high fields. An enhanced volume input is possible at high fields in special anti-resonance regimes when the excitation of the electrostatic wave is suppressed. The effective collision frequency is introduced to describe effective damping of helicon waves arising due to their conversion into electrostatic waves. The results obtained permit explanation of both measured field profiles and the high absorption efficiency in helicon sources.

The concept of the 'resonance' wave discharge is introduced to explain the high absorption efficiency of inductively coupled helicon plasma source. This discharge is supported by long-scale weakly damped eigenmodes.excited in plasma resonator. The rf power absorbed in it is inversely proportional to electron collision frequency. The fields excited by simple single-loop inner antenna and its impedance are calculated in a cylindrical metal resonator. At low collision frequencies the field amplitudes and antenna resistance are shown to peak sharply near the helicon dispersion branches.

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The excitation of a helicon plasma source by an azimuthally symmetric antenna is considered in comparison with anti-symmetric excitation. The resonances and anti-resonances at the wave excitation, as well as the peculiarities of the power absorption, are shown to be very similar for symmetric and anti-symmetric excitation. The plasma resistance turns out to be higher in the case of symmetric excitation for very short devices. The non-monotonic variation of plasma resistance with density is found to be intrinsic for both methods of excitation as a result of decreasing the power absorption at anti-resonances. This is shown to give rise to abrupt density jumps at varying input power.