Observation of turbulence exponential wave number spectra at ion sub-Larmor scales in FT-2 tokamak

Implementation of the correlative enhanced scattering technique in the FT-2 tokamak has resulted in measurements of both frequency and wave number spectra of a small-scale microturbulence. It is found that during the dynamic current ramp-up discharge the turbulence possesses a wide wave number spectrum which could be described by universal exponential dependence in the range of 3–4 orders of amplitude characterized by two parameters—the turbulence level and scale length. Both parameters are found to decrease substantially when the shear of the poloidal plasma rotation estimated from Doppler frequency shift of the enhanced scattering signal increases at plasma periphery. Simultaneously transition to an improved confinement resulting in the suppression of anomalous electron transport and decrease in the electron energy confinement time is observed in the experiment.