Azimuthal inhomogeneity of turbulence structure and its impact on intermittent particle transport in linear magnetized plasmas

T Kobayashi,K Itoh,Y Kosuga,A Fujisawa,M Sasaki,S.-I Itoh,N Kasuya,S Inagaki,Y Miwa,Y Nagashima,T Yamada,H Arakawa

doi:10.1063/1.4934537

Abstract

Fluctuation component in the turbulence regime is found to be azimuthally localized at a phase of the global coherent modes in a linear magnetized plasma PANTA. Spatial distribution of squared bicoherence is given in the azimuthal cross section as an indicator of nonlinear energy transfer function from the global coherent mode to the turbulence. Squared bicoherence is strong at a phase where the turbulence amplitude is large. As a result of the turbulence localization, time evolution of radial particle flux becomes bursty. Statistical features such as skewness and kurtosis are strongly modified by the localized turbulence component, although contribution to mean particle flux profile is small.

Highlights

Anomalous transport caused by plasma turbulence has been regarded as a principal obstacle for the realization of a thermonuclear fusion reactor for many years.Nondiffusive and nonlocal properties of plasma transport have been intensely studied since the 1980s [1], and recently the importance of global structures driven by turbulence, e.g., zonal flows [2, 3, 4, 5], streamers [6, 7], and a long-distance radial correlation modes [8], has been noted in both experimental and numerical works
These global structures can break the symmetry of turbulence [9], which is a key factor for explaining nondiffusivity or nonlocality and intermittency of transport
According to the azimuthal correlation length of fluctuations, the fluctuation component was divided into two different regimes, the coherent regime and the turbulence regime

Summary

Introduction

Anomalous transport caused by plasma turbulence has been regarded as a principal obstacle for the realization of a thermonuclear fusion reactor for many years. Nondiffusive and nonlocal properties of plasma transport have been intensely studied since the 1980s [1], and recently the importance of global structures driven by turbulence, e.g., zonal flows [2, 3, 4, 5], streamers [6, 7], and a long-distance radial correlation modes [8], has been noted in both experimental and numerical works. These global structures can break the symmetry of turbulence [9], which is a key factor for explaining nondiffusivity or nonlocality and intermittency of transport.

Experimental apparatus

Experimental results

Discussion and summary