Comparison between kinetic-ballooning-mode-driven turbulence and ion-temperature-gradient-driven turbulence

運動論的バルーニングモード乱流とイオン温度勾配駆動乱流の比較

前山 伸也; 石澤 明宏*; 渡邉 智彦*; 仲田 資季; 宮戸 直亮; 矢木 雅敏; 井戸村 泰宏   

Maeyama, Shinya; Ishizawa, Akihiro*; Watanabe, Tomohiko*; Nakata, Motoki; Miyato, Naoaki; Yagi, Masatoshi; Idomura, Yasuhiro

Electromagnetic turbulence driven by kinetic ballooning modes (KBMs) in high-beta plasma is investigated based on the local gyrokinetic model. Analysis of turbulent fluxes, norms and phases of fluctuations shows that KBM turbulence gives narrower spectra and smaller phase factors than those in ion-temperature-gradient (ITG)-driven turbulence. This leads to the smaller transport fluxes in KBM turbulence than those in ITG turbulence even when they have similar linear growth rates. From the analysis of the entropy balance relation, it is found that the entropy transfer from ions to electrons through the field-particle interactions mainly drives electron perturbations, which creates radially twisted modes by rapid parallel motions of electrons in a sheared magnetic geometry. The nonlinear coupling between the dominant unstable mode and its twisted modes is important for the saturation of KBM turbulence, in contrast to the importance of zonal flow shearing in ITG turbulence.