Fast excitation of geodesic acoustic mode by energetic particle beams

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 functio...

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Bibliographic Details
Published in:Physics of plasmas 2015-12, Vol.22 (12)
Main Authors: Cao, Jintao, Qiu, Zhiyong, Zonca, Fulvio
Format: Article
Language:English
Subjects:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY
DISTRIBUTION FUNCTIONS
Energetic particles
EXCITATION
GEODESICS
INCLINATION
INSTABILITY GROWTH RATES
LHD DEVICE
MATHEMATICAL SPACE
PARTICLE BEAMS
Pitch (inclination)
Plasma physics
SOUND WAVES
VELOCITY
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Summary: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.
ISSN:1070-664X
1089-7674
DOI:10.1063/1.4938277