The results of a study of the statistical space/time properties of the turbulence observed in the edge region of the Pretext tokamak are reported. A local estimate of the wavenumber frequency spectra S(k, w) for poloidal (k y ) and toroidal (k z ) wavenumbers is determined for the range 0.5 cm" 1 < k < 7.5 cm" 1 , for both potential and density fluctuations obtained from spatially fixed Langmuir probe pairs. The S(k y ,co) spectra are dominated by low frequencies (< 200 kHz) and small wavenumbers (< 3 cm" 1 ) and appear broadened about an approximately linear statistical dispersion relation, k (co). The broadening is characterized by a spectral width a k (co) (root-mean-square deviation about k (to)) which is of the order of k (CJ). The turbulence appears to propagate poloidally with an apparent mean phase velocity of (1 -2) X 10 s cm • s" 1 in the ion diamagnetic drift direction. Measurements of the fluctuation-induced particle transport reveal the particle flux to be outward and resulting primarily from the low-frequency, long-wavelength components of the turbulence. A particle diffusion coefficient D x> estimated from the measured particle flux and density profiles, is of the order of the coefficient estimated for Bohm diffusion, but appears to increase with density.

A reversal has been observed in the mean phase velocity of the turbulent fluctuations in the edge plasma of the TEXT tokamak. The observations can be described by a model in which the wave velocity in the lab frame is dominated by a nonuniform Er×B velocity and a gradient driven drift. The measurements also exhibit a localized instability which occurs in the region of maximum velocity shear.

The spectra, magnitude and spatial distribution of low-frequency (w <3 w ci ) density fluctuation have been measured by two independent experimental methods in the edge plasma of the TEXT tokamak. Good agreement between far-infrared laser scattering and Langmuir probe measurements has been achieved and the strengths of each technique are evaluated. Langmuir probes are used to directly determine the particle flux induced by edge fluctuations (F oc (ni>£ xB )) and collective Thomson scattering permits an extension of these observations to the plasma interior. Results are presented for typical discharge conditions in a tokamak.

No abstract