Plasma and Fusion Research

Volume 4, 008 (2009)

Regular Articles

Numerical Study of the Ripple Resonance Diffusion of Alpha Particles in Tokamaks
Hideyuki MIMATA, Keiji TANI1), Hiroaki TSUTSUI, Kenji TOBITA2), Shunji TSUJI-IIO and Ryuichi SHIMADA
Tokyo Institute of Technology, Tokyo 152-8550, Japan
1)
Nippon Advanced Technology Co., Ltd. Naka Office, Naka 311-0193, Japan
2)
Japan Atomic Energy Agency, Naka 311-0193, Japan
(Received 30 September 2008 / Accepted 16 January 2009 / Published 16 March 2009)

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.

Keywords

α particle, tokamak, particle diffusion, ripple resonance, mapping model, Poincaré map

DOI: 10.1585/pfr.4.008

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This paper may be cited as follows:

Hideyuki MIMATA, Keiji TANI, Hiroaki TSUTSUI, Kenji TOBITA, Shunji TSUJI-IIO and Ryuichi SHIMADA, Plasma Fusion Res. 4, 008 (2009).