Qu, Zhisong; Hole, Matthew; Fitzgerald, Michael
An unstable branch of the energetic geodesic acoustic mode (EGAM) is found using fluid theory with fast ions characterized by their narrow width in energy distribution and collective transit along field lines. This mode, with a frequency much lower than the thermal GAM frequency ωGAM, is now confirmed as a new type of unstable EGAM: a reactive instability similar to the two-stream instability. The mode can have a very small fast ion density threshold when the fast ion transit frequency is...[Show more]
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