Key effects on the core confinement improvement of AUG hybrid scenario

Hybrid mode is a prime candidate for long-pulse/steady-state operation in future fusion reactors. Transport analysis of a fully non-inductive high performance ASDEX Upgrade(AUG) hybrid shot(A.Bock, Nuclear Fusion, 2017) is performed. It is shown that the confluence of several mechanisms is essential for the improvement in core confinement. In addition to the rotation shear, low magnetic shear, which is a common characteristic near the magnetic axis of hybrid scenario, is found to be favorable for both electromagnetic and alpha stabilization. Together they prepare the stage such that the presence of fast ions facilitates the transition to a strong local ITB due to additional dilution effect and enhancement of alpha stabilization. This study presents for the first time that a quasilinear turbulent model is capable of quantitatively matching the experiment temperature profile across the entire core. Such a model can thus be used with confidence to design hybrid operating scenarios for ITER and CFETR.