Instabilities with frequency chirping in the frequency range of Alfvén eigenmodes have been found in the domain 0.1% < 〈β h〉 < and v b||/v A ∼ 1 with high energy neutral beam injection in JT-60U. One instability with a frequency inside the Alfvén continuum spectrum appears and its frequency increases slowly to the toroidicity induced Alfvén eigenmode (TAE) gap on the timescale of an equilibrium change (≈200 ms). Other instabilities appear with a frequency inside the TAE gap and their frequencies change very quickly by 10-20 kHz in 1-5 ms. During the period when these fast frequency sweeping (fast FS) modes occur, abrupt large amplitude events (ALEs) often appear with a drop of neutron emission rate and an increase in fast neutral particle fluxes. The loss of energetic ions increases with a peak fluctuation amplitude of B̃ θ/B θ. An energy dependence of the loss ions is observed and suggests a resonant interaction between energetic ions and the mode.
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