Observation of asymmetric power spectra of density fluctuations in the JIPP T-IIU plasma by far-infrared laser scattering

Abstract

Asymmetric power spectra of the density fluctuations in the JIPP T-IIU plasma have been observed by submillimetre wave scattering using a newly developed dual homodyne detection system. A linear dispersion relation between the frequency at the peak of the broad spectra of the density fluctuations and the poloidal wave number kθ has been obtained. The observed frequencies are about three times higher than the theoretical values for electron diamagnetic drift waves. It is shown that this discrepancy can be accounted for quantitatively by the Doppler effect due to the fluid rotation of the plasma. Low frequency line spectra are also observed, exclusively for low kθ; they are identified with MHD waves. Finally, it is pointed out that the extended scattering region could have significant effects on the apparent spectral distribution of the density fluctuations.