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V. A. Vershkov, S. V. Soldatov, D. A. Shelukhin,
V. V. Chistyakov
Russian Research Center ``Kurchatov Institute'' 123182 Moscow, Russia
Abstract. The physical mechanisms of small-scale density fluctuations in the
frequency range 5 - 500 kHz have been investigated with correlation
reflectometry in different types of ohmicaly heated discharges. A temporal
formation of velocity shear in the central region of plasma column during the
discharge transition from Saturated to Improved Ohmic Confinement results in
suppression of long wavelength quasi-coherent turbulence, while the amplitude
of fluctuations with shorter wavelength is not affected. The potential of
correlation reflectometry was extended by simultaneous plasma probing from Low
Field Side and High Field Side. A factor of 5 enhancement of quasi-coherent
turbulence at Low Field Side was measured, while the other turbulence type is
poloidally symmetrical. Nearly 100 % long distance toroidal correlation was
observed for quasi-coherent density fluctuations at a distance of 10 meter
after one turn around tokamak major axis. Fluctuations propagate at an angle
of about 0.5
owith respect to the perpendicular to the magnetic field
line, proving a drift mechanism of turbulence. A plasma rotation was estimated
from the radial force balance equation for ions with the radial electric
field, measured with heavy ion beam probe diagnostic. A comparison of the
calculated plasma rotation with measured turbulence one show that the
turbulence rotates in ion diamagnetic drift direction in a plasma frame. All
experimental observations are consistent with Toroidal and Slab ITG turbulence
physical mechanism.
IAEA 2001
