Interplay between zonal flows/GAMs and ITG turbulence in tokamak plasmas

トカマクプラズマ中の帯状流GAMとイオン温度勾配駆動乱流との相互作用

宮戸 直亮; 岸本 泰明; Li, J. Q.*

Miyato, Naoaki; Kishimoto, Yasuaki; Li, J. Q.*

トカマクプラズマ中の帯状流の振舞いと、それが乱流輸送に及ぼす影響を静電的なイオン温度勾配駆動乱流のグローバル流体シミュレーションによって調べた。高安全係数領域で現れるGeodesic Acoustic Mode(GAM)と呼ばれる、時間的に振動する帯状流はプラズマの小半径方向に同一の周波数を持つという非局所性を示す。正磁気シアトカマクにおいて(はイオンのラーモァ半径,はプラズマの小半径)を変化させたシミュレーションを行い、非局所性を特徴づける長さがに比例することを明らかにするとともに、GAMが支配的な高輸送領域と静的帯状流が支配的な低輸送領域とをつなぐ領域の長さがと関係があることを示した。また、反転磁気シアプラズマにおける帯状流の振る舞いについても明らかにした。

Zonal flow behaviour and its effect on turbulent transport in tokamak plasmas are investigated by global fluid simulations of electrostatic ion temperature gradient (ITG) driven turbulence. It is found that oscillatory zonal flows called geodesic acoustic modes (GAMs) appearing in a high (safety factor) region have the same frequency in a certain radial region whose width is almost proportional to in positive shear tokamaks, and the radial wavelength of the GAMs is proportional to , where is an ion Larmor radius and is a minor radius of a plasma. The turbulent transport is affected by the nonlocal behaviour of the GAMs. It seems that the radial width of the region connecting a low tranport region where the stationary zonal flows are dominant with a high transport region where the GAMs are dominant is related with the nonlocal width of the GAMs. In reversed shear tokamaks with high , turbulent transport is high even in a minimum region because the GAMs are dominant. The turbulent transport is reduced in the minimum region when is enough low to damp the GAMs. The difference of zonal flow behaviour causes the difference of the turbulent transport and may trigger formation of ion internal transport barriers in both positive and reversed shear tokamaks.