SELF-ORGANIZED CRITICAL GRADIENT TRANSPORT AND SHEAR FLOW EFFECTS FOR THE ION TEMPERATURE GRADIENT MODE IN TOROIDAL PLASMAS

摘要

Non-local turbulence driven by the toroidal ion temperature gradient (ITG) mode is found to provide a strong constraint on plasma relaxation and transport and forces a relaxed state near (but slightly above) marginal stability. The transport characterized by such a prominent feature is investigated in terms of a critical gradient model which includes the shear flow effect. The model leads to L mode scaling with Bohm-like diffusivity when ideal radial modes are well sustained. The radial modes can be disintegrated into smaller radial islands by the poloidal shear flow, suggesting that the transport changes from Bohm-like to near gyro-Bohm. Poloidal momentum deposition couples with the turbulent energy and is found to lead to a new, strongly transport suppressed branch.