Using a global gyrofluid code, we conduct comprehensive flux-driven simulations incorporating external heat and momentum sources/sinks. They involve an external torque ramp while keeping a heating power constant. Simulations show the formation of internal transport barriers (ITBs) in ion heat and parallel momentum in weak magnetic shear configuration. The ITB formation is attributed to the reduction of turbulent transport accompanied by strong flow shear generation, where the majority of shear arises from plasma rotation shear. In contrast, only a minor confinement improvement is observed in strong magnetic shear configuration. There exists a substantial difference in the rotation shear between the weak and strong magnetic shear cases at the same amount of external torque. Transport analysis implies that the difference comes from intrinsic rotation generated by residual stress. Global linear simulations demonstrate that the effect of shear on symmetry breaking is enhanced in weak magnetic shear configuration, explaining the origin of the difference in intrinsic rotation. The ITB is not achieved when the external torque is injected in counter-direction to intrinsic rotation. It is also shown that threshold torque for the ITB formation depends on power and the ratio of external torque to heating power should exceed a critical value to attain an ITB.
この論文では、外部トルクの印加による内部輸送障壁(ITB)の形成過程をグローバルなジャイロ流体シミュレーションで解明しています。弱い磁気シア構成では、強いシアフローの発生により輸送が抑制されITBが形成されますが、強い磁気シア構成では顕著な改善は見られません。これは、弱い磁気シア時の内在的回転の増大が重要な役割を果たしていることを示しています。