Study of drift wave turbulence by microwave scattering in a toroidal plasma

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Abstract
A study of drift wave turbulence by microwave scattering technique was carried out in a toroidal plasma confinement device, the FM-1 spherator. The principal results are; (a) Observation of the linear dispersion relation of drift waves in the high magnetic shear condition. The linear dispersion relation is followed up to weak turbulence state (..gamma.. approximately less than ..omega..). (b) An experimental demonstration of the stabilization of the drift waves with an increase of the shear strength. In particular, the ion mass dependence of the observed marginal stability criterion for drift waves (..omega.. approximately ..omega../sub */ was in reasonably good agreement with theoretical expectations. Further, very low frequency (..omega.. much less than ..omega../sub */) fluctuations were enhanced when the shear strength was lowered. (c) A detailed study of the behavior of drift waves in a weak shear condition where a state of isotropic turbulence was observed. The turbulent density fluctuations showed a strong dependence on frequency, but no dependence on wave number (somewhat in sharp contrast to theoretical expectations). The possible dependence of the anomalous loss process on the observed drift wave turbulence is also discussed.

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