A new mechanism for geodesic acoustic mode (GAM) excitation by a not fully slowed down energetic particle (EP) beam is analyzed to explain experimental observations in Large Helical Device. It is shown that the positive velocity space gradient near the lower-energy end of the EP distribution function can strongly drive the GAM unstable. The new features of this EP-induced GAM (EGAM) are: (1) no instability threshold in the pitch angle; (2) the EGAM frequency can be higher than the local GAM frequency; and (3) the instability growth rate is much larger than that driven by a fully slowed down EP beam. © 2015 AIP Publishing LLC.
Titolo: | Fast excitation of geodesic acoustic mode by energetic particle beams |
Autori: | |
Data di pubblicazione: | 2015 |
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Handle: | http://hdl.handle.net/20.500.12079/2365 |
Appare nelle tipologie: | 1.1 Articolo in rivista |