Investigation of key factors for ITB formation and maintenance in EAST high ?N discharges

Long-pulse high beta N operation scenario with internal transport barrier (ITB) and central flat q profile has been achieved on EAST. Analysis shows that higher heating power is needed to obtain ITBs in higher density discharges. Analysis of EAST high beta N experiments shows that fishbone activities are accompanied with formation ITB and high performance. Experimental and simulation analysis demonstrates that the increasing E x B shear flow by the neutral beam injection (NBI) is important for the formation of ion temperature ITB (Ti-ITB). And, Ti-ITB disappears with the reduction of plasma rotation. While ITBs in channels of electron density (ne) and temperature (Te) are not achieved until fishbone activities are observed, which means that E x B shear flow mainly affects the formation of Ti-ITB in EAST high beta N experiments. Experimental analysis shows that the fishbone is accompanied by the increasing E x B shear flow, leading to the formation of Ti-ITBs. A possible explanation for the formation of ITBs in all channels is that fishbone activities in high beta N discharges with central flat q-profiles (closed to unity) induce the feedback process of the formation of ITBs, and leading to the increase of E x B shear flow as well as the formation and sustainment of ITBs.(c) 2023 Elsevier B.V. All rights reserved.