Neutral beam injection induced discrete Alfvn instabilities on experimental advanced superconducting tokamak

Abstract

The neutral beam injection (NBI) system is applied to the experimental advanced superconducting tokamak (EAST). It will excite some Alfvn instabilities when the plasma characteristics are improved. The numerical research on the NBI-induced discrete Alfvn eigenmode (TAE) and toroidal effect-induced Alfvn eigenmode (TAE) in the pedestal region is presented in the paper. The research results show that plenty of TAEs appear in this region. The TAE is very different from the TAE. These modes are trapped by the -induced potential wells along the magnetic field line. Due to negligible continuum damping via wave energy tunneling, similar to TAE, the TAE can also be readily destabilized by energetic particles. Differently, TAE frequency spectrum is more broad than TAE, and they are existed not only inside the gap but also outside the gap. The growth rate increases with injected power increasing. This instability maybe affects the physical behavior of the tokamak and the confinement of the plasma.