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|
|Data di pubblicazione:||2015|
|Appare nelle tipologie:||1.1 Articolo in rivista|