Evidence for coherent structures within tokamak plasma turbulence

Coherent structures of density fluctuations have been observed in the shear region of poloidal rotation of the CT-6B tokamak plasma by analyzing the measured H_α line emission with a wavelet correlation technique. The structures exhibit strong temporal and spatial intermittency with a lifetime of 20--100 {μ}s and a radial size greater than or equal to 1 cm. The fluctuation shows a skewed non-Gaussian probability density function in the region where the coherent structures occur.