Plasma and Fusion Research
Online ISSN : 1880-6821
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Numerical Study of the Ripple Resonance Diffusion of Alpha Particles in Tokamaks
Hideyuki MIMATAKeiji TANIHiroaki TSUTSUIKenji TOBITAShunji TSUJI-IIORyuichi SHIMADA
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2009 Volume 4 Pages 008

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Abstract

The energy dependence of the diffusion coefficients of α particles in rippled fields of tokamaks is numerically investigated with an orbit-following Monte Carlo code. The diffusion coefficients are enhanced around the ripple resonance energy while they are not so much enhanced in the neighborhood of it. Consequently, they have a local minimum near the resonance energy, and hence they have an M-shaped energy dependence. Ripple resonance is caused by a radial change of the toroidal precession of banana particles, and creates islands in (Nφ, ψ) phase space. Since particles outside the separatrix are the main contributors to diffusion enhancement, the M-shaped energy dependence is explained by the co-existence of open and closed orbits in the phase space. Ripple resonance diffusion is dominant for fusion-produced α particles since the resonance energy width occupies a large portion of the energy range in their slowing-down processes.

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© 2009 by The Japan Society of Plasma Science and Nuclear Fusion Research
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