Frequency chirping of core-localized toroidicity-induced alfvén eigenmodes and their coupling to global alfvén eigenmodes

The fast frequency change or chirping of core-localized toroidicity-induced Alfvén eigenmodes (C-TAE), excited before giant sawteeth during ion cyclotron resonance heating, has been investigated. The chirping can be accounted for by small changes of the central q profile. When the C-TAE crosses the frequency of a global TAE (G-TAE) a small frequency gap was found. These gaps can be attributed to mode coupling between the C-TAE and a G-TAE which is observed for the first time. The coupling and the frequency gaps are consistent with linear TAE mode coupling.