Transition from unbounded to bounded whistler wave dispersion: Reconsidered

The whistler wave dispersion relation in the transition region between unbounded and bounded plasma geometry is investigated experimentally and numerically. Measurements are done in a linear magnetized helicon plasma covering the large frequency range from 100-800 MHz, corresponding to 0.06-0.5fce. Small wavelength wave propagation (λ<<d: plasma diameter) is well explained by unbounded plasma whistler wave dispersion. In contrast to previously reported measurements [Franck et al., Phys. Plasmas 9, 3254 (2002)], the experimental findings are compared to numerical results obtained from the differential equations of a plasma-filled waveguide. Long wavelength wave measurements show that there is only qualitative agreement even with dispersion theory of whistler wave propagation in bounded plasmas. This is attributed to the perpendicular wave mode structure that influences the parallel wavelengths. Measurements of the perpendicular wave mode structure shows that it is basically given by the diameter of the plasma column diameter rather than the conducting vessel with a dependence on the wave frequencies; two findings which are neglected so far in simple theory. These results are fully consistent with the numerical solutions