国際発表 | 11th Toki Conference

Radial Dependence of Collisionless Trapped Ion Mode on Pressure and q Profiles

Jiquan Li^a,b, Y. Kishimoto^a, T. Tuda^a, and Jinhua Zhang^b
a) Naka Fusion Research Establishment, JAERI, Naka, Ibaraki, 311-0193 Japan
b) Southwestern Institute of Physics, P.O.Box 432, Chengdu, Sichuan, P.R.China

Abstract.
A radial eigen equation of the collisionless trapped ion mode(CTIM) has been rederived from the drift-kinetic equation by directly retaining the finite banana orbit width effect on the non-adiabatic portion of the perturbed distribution, rather than employing the usual expansion < f(r, q) > = f(r₀) + r_bi²d² f(r₀) / dr₀² (here < ^{. . .} > indicates the bounce averatge). The resultant equation includes the effects of all banana orbits with different width on the radial mode structure. Based on this radial eigen mode equation, local and non-local stability analyses of CTIM for a peaked pressure gradient profile has been presented. Meanwhile, the dependence of the radial eigen structure of CTIM on the pressure and q profiles has been studied in detail. The main results are summarized as follows: (1) There exist two pairs of unstable branches of CTIM in parameter region with steep pressure gradient. The branches with lower real frequency connect to the residual trapped ion modes. When electrons are taken as adiabatic, only two ion branches can be excited. One with higher frequency possesses toroidal mode structure and is strongly stabilized by the non-adiabatic passing ion dynamics. The other with lower frequency has a slab-like structure, and it is weakly stabilized by passing ion response and its growth rate weakly depends on the equilibrium pressure profile. This is the more important CTIM instability. (2) Under including the non-adiabatic passing ion response, the radial eigen structure of CTIM is dominated by the competition between the non-adiabatic trapped ion and passing ion dynamics. The former is governed by the equilibrium pressure profile and the magnetic trapping, and the latter strongly depends on the q-profile. Finally, the radial mode structure is discussed related to the results from the two-dimensional eigenmode code and from the observation in the toroidal particle simulation.