Recent progress of Alfven eigenmode experiments using N-NB in JT-60U tokamak

Bursting modes in the frequency range of the toroidicity induced Alfven eigenmode are observed in the plasma to which the negative-ion-based neutral beam (N-NB) is injected. A bursting mode changes its frequency by 10-20 kHz, in 1-5 ms and is called fast frequency sweeping (fast FS) mode. Another bursting mode evolves explosively in less than or equal to400 mus and is called an abrupt large-amplitude event. The dependence of their saturation level was compared with the experimentally observed growth rate and damping rate. The mode amplitude increases with the observed growth rate for fast FS modes. The modes with large amplitude and a large enhanced transport were observed when a large neutron emission rate was observed. The burst period increases as the drop ratio of the neutron emission increases.