Effects of Er shear on edge turbulence of the China Tokamak-6B

On the China Tokamak (CT-6B) [Nucl. Fusion 36, 1669 (1996)], application of negative limiter bias resulted in enhanced $E_r$ shear in the naturally occurring $E_r$ shear layer near the fixed limiter radius with negligible change of plasma density, electron temperature, the parallel plasma flow, and the impurity ion radiation power. In the layer, decreased turbulent fluctuation, reduced poloidal correlation and increased nonlinear coupling of the turbulence were observed to be very possibly correlated with enhanced $E_r$ shear. The results suggest that there exists interaction of $E_r$ shear with turbulence, and an $E_r$ shear-induced shift in the phase angle between density and poloidal electric field fluctuations and nonlinear three-wave coupling may play an important role in suppressing edge turbulence.