Resistive fluid turbulence in diverted tokamaks and the edge transport barrier in H-mode plasmas

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Abstract
The thermal and particle diffusivities driven by resistive fluid turbulence in diverted tokamak edge plasmas are calculated. Diverted tokamak geometry is characterized by increased global shear near the separatrix and the tendency of field lines to linger near the x point. For resistive fluid turbulence, the dominant effect is increased global shear, which causes a reduction in the effective step size of the turbulent diffusion process and corresponding improvements in heat and particle confinement close to the separatrix. Stability of resistive kink modes resonant near separatrix is also ensured by the increased global shear. The relevance of these considerations to the L→H transition and to the edge transport barrier in H‐mode plasmas is discussed.