The physical features of discrete Alfvén eigenmodes (αTAEs) bounded by the α-induced potential wells are investigated in ITER (International Thermonuclear Experimental Reactor) with the ITB (internal transport barrier) scenario, where α denotes a measure of the pressure gradient. The use of the negative-ion-based neutral beam injection (NNBI) heating and current driving can obtain a large and strong ITB for higher performance, and the instability of αTAE in this scheme is discussed. The αTAEs during sustaining, shrinking and erosion of ITB are discussed upon the pure radio frequency scenario. It is found that αTAEs exist in the ITB region due to the steep pressure gradient. More αTAEs exist in scenarios with strong ITB and the frequencies of these eigenmodes are higher. Multiple αTAEs are readily destabilized in the presence of energetic particles. The frequency of the excited αTAEs increases with increasing beam energy. The high β_p scenario with ITB on DIII-D has many of the desired properties of ITER steady-state. The αTAEs in high β_p scenarios are also studied.

In this paper, the instability of the discrete Alfvén eigenmodes (αTAEs, where α denotes a parameter of plasma pressure gradient) are simulated in the high performance plasma with internal transport barriers (ITBs) on the EAST. The simulation results show that there is an abundance of αTAEs on EAST, and it mainly locates in the core region within the ITB foot, where the temperature or the density gradient varies abruptly. Because the ITBs observed in the EAST are relatively localized and close to the core, the distribution of αTAEs in the radial radius is narrow.In the high performance scenario with localized magnetic shear reversal, the ITB region is closer to the plasma edge, the αTAEs locate in a larger radial region. However, in the ITB region, due to the strong negative magnetic shear, the αTAEs are only found near the ITB foot; the αTAEs frequency decreases as the pressure gradient decreases closer to the ITB foot. In addition, the αTAEs in the scenarios with localized magnetic shear reversal on the DIII-D and China Fusion Engineering Test Reactor (CFETR) are also compared, and it is similar to that on EAST, where the αTAEs do not exist in the strong magnetic shear region. The simulations on CFETR show that there are higher frequencies αTAEs in the core region and more abundant αTAEs are excited into unstable modes by energy particles.