A Signature of Self-Organized Criticality in the HT-6M Edge Plasma Turbulence

Power spectra of electron density and floating potential fluctuations in the velocity shear layer of the HT-6M edge region have been measured and analysed.All the spectra have three distinct frequency regions with the spectral decay indices typical of self-organized criticality systems(0,-1 and-4)when Doppler shift effects induced by the plasma E x B flow velocity have been taken into account.These results are consistent with the predictions of the self-organized criticality models,which may be an indication of edge plasma turbulence in the HT-6M tokamak evolving into a critical state independent of local plasma parameters.