Time Evolving Stucture of Alfvén Ion-Cyclotron Waves in GAMMA 10

A two-channel reflectometer has been developed and successfully applied to the GAMMA10 central cell to investigate the spatial structure of spontaneously excited Alfven ion-cyclotron (AIC) waves. At the frequencies of externally applied ICRF waves and AIC waves, good correlations of well above the statistical noise level are obtained between two density fluctuations at axially separated positions in the central cell. Density fluctuations at various radial positions and two axially separated positions show that the power distribution among the AIC waves changes much both in radial and axial directions especially in the earlier period just after the excitation and in the core region of r/a < 0.3. Phase differences of the AIC waves at axially separated positions show features of the transformation of the AIC waves from propagating to standing waves. The pass of the node of the standing wave is also observed. The time of the pass is different by AIC waves, which clearly indicates difference of the axial wavelengths of the simultaneously excited AIC waves.