Finite-β and alpha particle effects on kinetic Alfvén wave in a fusion tokamak plasma

Abstract

In this paper, a model for the kinetic Alfvén wave (KAW) in the presence of fusion alphas is established. The finite-β (relative to low β) and alpha particle effects on KAW are investigated. In this model, ion sound, transit time magnetic pumping (TTMP), the response of alpha particles (alphas), and those effects considered by preceding authors are included. In cylindrical geometry, a set of three second-order differential equations in r for the perturbed fields Er, E⊥, and E∥ is numerically solved. A dispersion relation of the Alfvén wave in the fusion tokamak plasma is derived. The mode conversion and the energy deposition are qualitatively discussed on the basis of this relation. Both the analytical and numerical analyses indicate that (i) no matter whether m (poloidal mode number) is positive [N. Ding et al., Phys. Plasmas 2, 1529 (1995)] or negative (mainly studied in the present paper), the alphas do not affect the compressional Alfvén wave, but they do affect the KAW evidently; (ii) for m<0, it is preferable to choose the frequency ω of the injected wave so that the inequality ω≳(Pm±1/Rm±1)−1ω*αm holds for optimal power absorption. The energy deposition at the resonant position close to the interior of the fusion tokamak plasma in taking account of the effects of ion sound and TTMP is less than that without taking account of these effects. But for the same β value, at the position adjacent to the edge the contrary is the case. For a certain resonant position, as the β value increases, the energy deposition decreases.