Key effects on the confinement improvement of the ASDEX Upgrade hybrid scenario

Abstract

Transport analysis of a fully non-inductive high performance ASDEX Upgrade (AUG) hybrid mode discharge (A.Bock, Nuclear Fusion, 2017) is performed using a gyro-fluid transport code and a gyro-kinetic stability code.It is shown that the confluence of several mechanisms is essential for the improvement in core confinement.In addition to rotation shear, low magnetic shear, which is a common characteristic near the magnetic axis of a hybrid scenario, is found to be favorable for both electromagnetic and α stabilization.Together they facilitate the conditions for fast ions to establish a strong local ITB by providing additional dilution effect and enhancement of α stabilization.This study provides a complete picture and demonstrates that a quasilinear turbulent model is capable of quantitatively matching the experimental temperature profiles across the entire core of a hybrid mode discharge.