The physical mechanisms of small scale density fluctuations in the frequency range5-400 kHz were investigated with correlation reflectometry in different types of ohmically heated discharges inthe T-10 tokamak. A temporal formation of velocity shear in the central region ofthe plasma column during the discharge transition from saturated to improved ohmicconfinement resulted in suppression of long wavelength quasi-coherent turbulence, while the amplitude of fluctuations with a broader frequency spectrum was not affected. The potential of correlation reflectometry was extended by simultaneous plasma probing from the low field side and high field side. Enhancement of quasi-coherent turbulence at the low field side by a factor of5 was measured, while the other turbulence type was poloidally symmetric. A high long distance toroidal correlation of up to 40% was observed experimentallyfor quasi-coherent density fluctuations at a distance of 10 m after one turnaround the tokamak major axis. Fluctuations propagate at an angle of about0.5° with respect to the perpendicular to the magnetic field line,demonstrating a drift mechanism of turbulence. Plasma rotation was estimatedfrom a radial force balance equation for ions with the radial electric fieldmeasured with a heavy ion beam probe. A comparison of the calculated plasmarotation with the measured turbulence rotation showed that the turbulence rotatesin the ion diamagnetic drift direction in the plasma frame. All experimentalobservations are consistent with `toroidal' and `slab' ion temperature gradientturbulence as the underlying physical mechanism.
Experimental study of the electromagnetic component of drift-wave turbulence