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(TH/P3-18) Simulation Study of Beam Ion Loss due to Alfvén Eigenmode Bursts

Y. Todo1), H.L. Berk2), B.N. Breizman2)
1) National Institute for Fusion Science, Toki, Japan
2) Institute for Fusion Studies, University of Texas at Austin, Austin, United States

Abstract.  Recurrent bursts of toroidicity-induced Alfvén 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 [K. L. Wong et al., Phys. Rev. Lett. 66, 1874 (1991)] are reproduced using the experimental parameters. It is found that synchronized TAE bursts take place at regular time intervals of 2.5 ms, which is fairly close to the experimental value of 2.2 ms. The stored beam energy saturates at 10% of that of the classical slowing-down distribution. This is consistent with an important experimental aspect that the beam confinement time is much shorter than the collisional slowing-down time. The stored beam energy drop associated with each burst has a modulation depth of 20% which is comparable to the inferred experimental value of 7%. This is the first simulation that reproduces all of these experimental aspects. The beam ion distribution hovers around a marginal stability state. Test particle analysis demonstrates that the disappearance of KAM surfaces in a coordinate system co-moving with each eigenmode leads to beam ion loss.

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IAEA 2003