Experimental evidence for self-organized criticality in tokamak plasma turbulence

Measurements of plasma turbulence spectra and particle flux from the DIII-D tokamak exhibit significant agreement with predictions of self-organized c riticality (SOC) modeling. Power spectra of density (n) over tilde, potenti al <(phi)over tilde>, and particle flux Gamma, are observed to have three r egions of frequency dependence: f(0), f(-1) and f(-4). In addition, the par ticle flux probability distribution displays a Gamma(-1) scaling over two d ecades in Gamma. These results provide the first evidence that the plasma i s in a state consistent with SOC models and place a constraint on plasma tr ansport models. (C) 1999 Elsevier Science B.V.