Localized modulation of turbulence by m / n =1/1 magnetic islands in the HL-2A tokamak

Modulation of turbulent electron temperature fluctuations ((T ) over tilde (e)) and density fluctuations ((n) over tilde (e)) by an m/n = 1/1 tearing mode island was observed in the core plasma region of the HL-2A tokamak. High spatiotemporal resolution two-dimensional images of (T) over tilde (e) show the first evidence that the turbulence modulation occurs only when the island width exceeds a certain threshold value (w(c) approximate to 10 rho i approximate to 4 cm) and the modulation is localized merely in the inner area of the island due to significant alteration of local profiles and turbulence drives. Evidence also reveals that for large islands turbulence spreading takes place across the island region. The results are generally consistent with theories and simulations.