Electrostatic fluctuations and turbulent, transport studies in the HT-7 superconducting tokamak edge plasmas

Electrostatic fluctuations and turbulence-induced particle flux have been investigated in the plasma boundary region of the HT-7 superconducting tokamak. There is a poloidal velocity shear layer driven by E-r x B-T located in the vicinity of the limiter radius, which has a suppression effect on the fluctuations and results in reductions in the normalized fluctuation level, coherence between the two plasma parameter fluctuations of <(<phi>)over tilde>(p) (T) over tilde (e) and (n) over tilde (e). The radial decorrelation effect of the poloidal velocity shear causes a decrease in the turbulent flux. The time evolution of the turbulent flux shows bursts in turbulent transport. The frequency range where the turbulent flux, which comes in bursts, is dominant has been identified. It is in this frequency range that the spectral region with power decay close to 1/f of the power spectrum of the floating voltage fluctuation has been found. This result could be a signature of the turbulent transport close to instability threholds.