Excitation of MHD surface waves propagating with shear Alfven waves in an inhomogeneous cylindrical plasma

Abstract

Experimental results are presented which show that the MHD surface waves or fast waves of m=+or-1 have been excited in the range of frequency less than ion cyclotron frequency using a helical antenna in a finite beta and cylindrical plasma. Their dispersion relation and spatial structure were successfully confirmed after the wave signals were separated from those of the local shear Alfven waves that propagated together with the surface waves. In order to obtain the dispersion relations from the signals, the authors adopted three kinds of methods: (1) conventional cross-power spectrum density using fast Fourier transform, (2) maximum entropy method, and (3) direct estimation of the phase velocity of wave packets. The observed properties of both the surface waves and the SAWs are in general agreement with theory.