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Author(s):
Y. Todo, H.L. Berk and B.N. Breizman
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Title:
Simulation Study of Beam Ion Loss due to Alfv始 Eigenmode Bursts
Date of publication:
Oct. 2002
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Key words:
IAEA, fusion energy conference, Lyon
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Abstract:
Recurrent bursts of toroidicity-induced Alfven eigenmodes (TAE) are studied using a self-consistent simulation model. Bursts of beam ion losses observed in the neutral beam injection experiment at the Tokamak Fusion Test Reactor are reproduced using experimental parameters. It is found that synchronized TAE bursts take place at regular time intervals of 2.9 ms, which is close to the experimental value of 2.2 ms. The stored beam energy saturates at 40% of that of the classical slowing down distribution. The stored beam energy drop associated with each burst has a modulation depth of 10% which is also close to the inferred experimental value of 7%. Surface of section plots demonstrate that both the resonance overlap of different eigenmodes and the disappearance of KAM surfaces in phase space due to overlap of higher-order islands created by a single eigenmode lead to particle loss. The saturation amplitude is delta B/B ~ 2 x l0^-2, is larger than would appear to be compatible with experiment, but reasons are given why our other results may be robust. The stored beam is primarily from co-injected particles when there is a limiter leaning on the inner edge.
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