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Phys. Rev. Lett. 71, 855–858 (1993)

Observation of beta-induced Alfvén eigenmodes in the DIII-D tokamak

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W. W. Heidbrink, E. J. Strait, M. S. Chu, and A. D. Turnbull
Department of Physics, University of California, Irvine, California 92717
General Atomics, P.O. Box 85608, San Diego, California 92186-9784

Received 8 March 1993; published in the issue dated 9 August 1993

Energetic ions can drive Alfvén gap modes unstable, causing large losses of fast ions. Toroidicity-induced Alfvén eigenmodes (TAE) were expected to disappear into the shear Alfvén continuum and become stable as the plasma beta increased. Although TAE modes may disappear, another dangerous instability with similar properties but approximately half the TAE frequency appears in a spectral gap that is created by finite beta effects. The measured frequency of the new mode agrees with the theoretical frequency of beta-induced Alfvén eigenmodes.

© 1993 The American Physical Society

URL:
http://link.aps.org/doi/10.1103/PhysRevLett.71.855
DOI:
10.1103/PhysRevLett.71.855
PACS:
52.55.Fa, 52.35.Bj, 52.55.Pi