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(TH/P1-08) Gyrokinetic Global Analysis of Ion Temperature Gradient Driven Mode in Reversed Shear Tokamaks

Y. Idomura1), S. Tokuda1), Y. Kishimoto1)
1) Japan Atomic Energy Research Institute, Ibaraki, Japan

Abstract.  The ion temperature gradient driven (ITG) mode in reactor relevant large tokamak parameters ( a/$ \rho_{i}^{}$ = 320 - 460) is studied using a newly developed gyrokinetic toroidal particle code. From comprehensive global analyses over a wide range of an unstable toroidal mode number spectrum (n=0-100), it is found that especially in reversed shear tokamaks, properties of the ITG mode are drastically changed through ion heating and density peaking processes. If the ion temperature is sufficiently high, high-n modes, which are much more unstable than low-n modes, are excluded from the qmin region of reversed shear tokamaks, because of a geometry effect 1/r and the finite Larmor radius effect in an unstable condition in a wave number space k$\scriptstyle \theta$$ \rho_{i}$ = nq(r)/r$ \rho_{i}$ = 0.5. On the other hand, these global effects become weak in normal shear tokamaks, because the effects are compensated by monotonically increasing q(r). Residual low-n global modes in the qmin region show slab like feature, and their growth rates decrease by a peaked density profile.

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IAEA 2003