Stabilization of Kinetic Internal Kink Mode by Ion Diamagnetic Effects

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Ion diamagnetic effects on the m=1 (poloidal mode number) and n=1 (toroidal mode number) kinetic internal kink mode are studied numerically by the three-field gyro-reduced-MHD code in the cylindrical coordinates, GRM3F-CY. In the derivation of the gyro-reduced-MHD model including the ion diamagnetic effects, finite gyroradius effects of ions are added to the gyrokinetic Poisson equation (quasineutral condition) and the convection term of the conservation law of the ion density. It is found that the long wavelength approximation, κ_⊥ρ_<ti><<1, where κ_⊥ is the wavenumber perpendicular to the magnetic field and ρ_<ti> is the thermal ion gyroradius, fails to reproduce the correct dispersion relation; the formulation valid even for κ_⊥ρ_<ti>>>1 is necessary. The results of numerical calculation coincide with the theory for |ω_<*e>|+|ω_<*i>|<2γ_0, where the growth rate reduces as the density gradient increases. Here ω_<*e> and ω_<*i> are electron and ion diamagnetic angular frequencies estimated at the rational surface of q=1 (q is a salty factor), respectively, and γ_0 is the growth rate for the uniform density. Very weak instability, however, is observed for |ω_<*e>|+|ω_<*i>|>2γ_0, where the theory predicts the complete stabilization. This residual instability appears since the region with the density gradient is limited in the radial direction and the stabilization by the outgoing drift-wave like mode becomes incomplete.
社団法人プラズマ・核融合学会の論文
2000-08-25

Stabilization of Kinetic Internal Kink Mode by Ion Diamagnetic Effects

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