Turbulent transport reduction induced by transition on radial electric field shear and curvature through amplitude and cross-phase in torus plasma

T Kobayashi,A Fujisawa,Y Nagashima,S.-I Itoh,S Inagaki,Y Miura,K Ida,K Itoh,T Ido,K Kamiya

doi:10.1038/s41598-017-14821-y

Abstract

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.

Highlights

Structure of flows and turbulence in non-equilibrium plasmas has attracted much attention because of its great impact on the entire media dynamics
It was found that the turbulent particle flux is reduced by the density fluctuation amplitude suppression and by the cross phase alternation between the density fluctuation and the potential fluctuation[19,20,21,22]
Dynamic inward transmission of a turbulence packet was observed in a limit cycle oscillation event[26]

Summary

Introduction

Structure of flows and turbulence in non-equilibrium plasmas has attracted much attention because of its great impact on the entire media dynamics. It was found that the turbulent particle flux is reduced by the density fluctuation amplitude suppression and by the cross phase alternation between the density fluctuation and the potential fluctuation[19,20,21,22]. Individual elements regarding the turbulent transport suppression by the inhomogeneous E × B flow have been raised, i.e., shear and curvature of E × B flow and amplitude and cross phase of fluctuations, the mutual relation of these elements remain unclear. The particle flux is suppressed predominantly by reducing both the density fluctuation amplitude and the cross phase between density fluctuation and potential fluctuation Both curvature and shear are responsible for transport reduction. Turbulence amplitude reduction immediately responds to the growth of the radial electric field non-uniformity and saturates, while cross phase continuously approaches zero. Turbulent transport reduction occurs with two different time scales

Methods

Results

Conclusion