Kobayashi T, Itoh K, Ido T, Kamiya K, Itoh S-I, Miura Y, Nagashima Y, Fujisawa A, Inagaki S, Ida K
National Institute for Fusion Science, National Institutes of Natural Sciences, Toki, 509-5292, Japan.
Institute of Science and Technology Research, Chubu University, Kasugai, 487-8501, Japan.
Sci Rep. 2017 Nov 2;7(1):14971. doi: 10.1038/s41598-017-14821-y.
Spatiotemporal evolutions of radial electric field and turbulence are measured simultaneously in the H-mode transition, which is a prototypical example of turbulence structure formation in high-temperature plasmas. In the dynamical phase where transport barrier is established abruptly, the time-space-frequency-resolved turbulent particle flux is obtained. Here we report the validation of the mechanism of transport barrier formation quantitatively. It is found that the particle flux is suppressed predominantly by reducing density fluctuation amplitude and cross phase between density fluctuation and potential fluctuation. Both radial electric field shear and curvature are responsible for the amplitude suppression as was predicted by theory. Turbulence amplitude reduction immediately responds to the growth of the radial electric field non-uniformity and saturates, while cross phase continuously approaches zero.
