A simple model is proposed to explain the recent experiment in TFTR and the more recent one in JT-60U.In the model the significant reduction of effective thermal diffusivities of ions and electrons(xieff and xeeff)is attributed to the inward flows of drift wave energy,induced by the synergistic effects of the reversed magnetic shear and E X B velocity shear,where E is due to ion pressure gradient.Numerical results demonstrate the predictions of the present model,in particular,the numerical results for x_(i)^(eff) are in good agreement with experimental trents.
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