Excitation of RSAEs during Sawteeth-Like Oscillation in EAST

The excitation condition of reversed shear Alfvén eigenmodes (RSAEs) has been investigated during sawtooth-like oscillation in the EAST tokamak. The sawtooth-like phenomena can be reproduced in the configuration of reversed magnetic shear, and the threshold gradient of electron temperature is formed accordingly, together with the increasing of the confinement of thermal particles. The distribution function of energetic ions density is altered dramatically when the neutral beam is switched from NBI1L (tangent) to NBI1R (perpendicular), which can be captured by the measurement of radial neutron camera. The RSAEs are excited easily in the vicinity of q_\min (1.99 m \leq R \leq 2.06 m) for the injection of neutral beam with perpendicular direction, which should be excited by the steep gradient of energetic ions density. Furthermore, the excitation of RSAEs and the formation of threshold gradient of electron temperature can take place concurrently, which means that the neutral beam with perpendicular injection is beneficial for the establishment of internal transport barrier.