Relation between a plasma confinement improvement due to internal transport barrier formation and the effects of sheared flows on the suppression of turbulent vortices

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Anomalous particle and energy cross-field transport is one of the most critical issues in magnetic plasma confinement for fusion, as well as in the physics of magnetized plasmas in general. In magnetic confinement systems with different magnetic-field topologies (e. g., tokamaks, stellarators, and mirrors), recent experiment shave shown that low-frequency (LF) turbulence and the associated anomalous cross-field plasma transport exhibit rather common features including high-confinement (H) mode transition sand internal transport-barrier (ITB) formation.The controlled formation of an internal transport barrier is investigated. The barrier is localized within a layer of a strongly sheared E_r×B plasma rotation. This high-vorticity layer is anticipated to be formed and maintained by plasma heating, which generates a layer with a partial loss of electrons that modifies the initial Gaussian radial potential profile into a non-monotonic one with a hump structure. The local gradients of T_I and T_e are also expected to be enhanced in the ITB layer, similarly to those of the ITB in tokamaks and stellarators. Reductions in the effective ion and electron thermal diffusivities are thus anticipated in the barrier layer A reduction of the observed low-frequency turbulence in the ITB layer and a partial decoupling of the turbulent structures localized on either side of the layer are demonstrated. Recently, we have obtained the ideas of various controlled methods, although unexpected matters disturbed their reports. These new methods will be extended in future.Such externally controlled transport barrier formation is of great importance for the fusion plasma upgrade including ITER plasmas in terms of the active control of the internal transport barrier formation.