Evolution of ETG-mode scale turbulence spectra and anomalous electron transport in dynamic experiments at FT-2 tokamak

The results of systematic investigations of the small-scale turbulence performed in dynamic fast current ramp up and lower hybrid (LH) heating experiments at FT-2 tokamak are reported. Both frequency and wave number (q) spectra are measured with correlative enhanced scattering diagnostics. It is found that during the dynamic discharge the turbulence component identified with the dissipative TEM mode possesses a wide qspectrum 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 increases at plasma periphery. Simultaneously suppression of anomalous electron transport is observed in the experiment. On contrary, the q-spectrum of the component, identified with the ETG mode, looks very different from exponential. It is characterized by pronounced maximum at wave number corresponding to the largest ETG instability growth rate. Its behavior, in agreement with the GS2 code predictions, in the dynamic LH heating experiment is correlated with the ratio of electron temperature and density scale lengths, but not with the electron thermal diffusivity.