title: Experimental Identification of Electric Field Excitation Mechanisms in a Structural Transition of Tokamak Plasmas.
abstract: Self-regulation between structure and turbulence, which is a fundamental process in the complex system, has been widely regarded as one of the central issues in modern physics. A typical example of that in magnetically confined plasmas is the Low confinement mode to High confinement mode (L-H) transition, which is intensely studied for more than thirty years since it provides a confinement improvement necessary for the realization of the fusion reactor. An essential issue in the L-H transition physics is the mechanism of the abrupt "radial" electric field generation in toroidal plasmas. To date, several models for the L-H transition have been proposed but the systematic experimental validation is still challenging. Here we report the systematic and quantitative model validations of the radial electric field excitation mechanism for the first time, using a data set of the turbulence and the radial electric field having a high spatiotemporal resolution. Examining time derivative of Poisson's equation, the sum of the loss-cone loss current and the neoclassical bulk viscosity current is found to behave as the experimentally observed radial current that excites the radial electric field within a few factors of magnitude.
authors.affiliation: National Institute for Fusion Science, Toki 509-5292, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Kobayashi
authors.affiliation: National Institute for Fusion Science, Toki 509-5292, Japan.|Research Center for Plasma Turbulence, Kyushu University, Kasuga 816-8580, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Itoh
authors.affiliation: National Institute for Fusion Science, Toki 509-5292, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Ido
authors.affiliation: National Institutes for Quantum and Radiological Science and Technology, Naka 311-0193, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Kamiya
authors.affiliation: Research Center for Plasma Turbulence, Kyushu University, Kasuga 816-8580, Japan.|Research Institute for Applied Mechanics, Kyushu University, Kasuga 816-8580, Japan.
authors.forename: S-I
authors.initials: SI
authors.lastname: Itoh
authors.affiliation: Japan Atomic Energy Agency, Tokai 319-1184, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Miura
authors.affiliation: Research Center for Plasma Turbulence, Kyushu University, Kasuga 816-8580, Japan.|Research Institute for Applied Mechanics, Kyushu University, Kasuga 816-8580, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Nagashima
authors.affiliation: Research Center for Plasma Turbulence, Kyushu University, Kasuga 816-8580, Japan.|Research Institute for Applied Mechanics, Kyushu University, Kasuga 816-8580, Japan.
authors.forename: A
authors.initials: A
authors.lastname: Fujisawa
authors.affiliation: Research Center for Plasma Turbulence, Kyushu University, Kasuga 816-8580, Japan.|Research Institute for Applied Mechanics, Kyushu University, Kasuga 816-8580, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Inagaki
authors.affiliation: National Institute for Fusion Science, Toki 509-5292, Japan.|Research Center for Plasma Turbulence, Kyushu University, Kasuga 816-8580, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Ida
authors.affiliation: National Institutes for Quantum and Radiological Science and Technology, Naka 311-0193, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Hoshino