A signature of self-organized criticality in the HT-6M edge plasma turbulence

Power spectra of electron density and Boating potential fluctuations in the velocity shear layer of the HT-GM 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 how 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 ill the HT-GM tokamak evolving into a critical state independent of local plasma parameters.