Experimental Study of Nonlinear Processes in Edge Turbulence of Toroidal Plasmas

Plasma Phys. Control. Fusion

et al. 2007

A method for zonal flow study by using direct density fluctuation measurements is proposed. When ambient drift-wave turbulence is modulated by zonal flows (i.e. in the drift-wave-zonal flow systems), an envelope of the ambient density fluctuations has spectral peaks around zonal flow frequencies. A spectral peak at the geodesic acoustic mode (GAM) frequency is observed in the envelope of the ambient density fluctuations measured in edge plasma of the JFT-2M tokamak. The significant cross-bicoherence is also found between the ambient density fluctuations and its envelope in the GAM frequency. This result demonstrates that we can measure the GAM only by using density fluctuation data. This method provides a possibility of zonal flow research in burning core plasma by density fluctuation diagnostics such as microwave reflectometry.

Section: Cross-spectral Analysis (Cross-coherence and Cross-phase)mentioning

confidence: 83%

In search of zonal flows by using direct density fluctuation measurements

Nagashima

Plasma Phys. Control. Fusion

et al. 2007

“…Figure 7 c shows the result of the bicoherence analysis of the spectrum in Fig. 7(b) [20,28]. The squared bicoherence,b 2 ( f 1 , f 2 ), and the biphase, Θ( f 1 , f 2 ), are given in Fig.…”

Section: Measurement Of Nonlinear Interactionmentioning

confidence: 98%

On Imaging of Plasma Turbulence

Plasma and Fusion Research

Fujisawa

Nagashima

et al. 2007

We discuss aspects of imaging of plasma turbulence, taking the standpoint that the imaging is a path for induction of law from complex signals. An example of induction of symbol from signals is illustrated. Then the image of plasma turbulence is extended, putting an emphasis on the identification of the nonlinear interaction in turbulence. By employing the bipspectral method, magnitudes of interactions among excited modes are estimated. Interactions between microscopic turbulence and large-scale structures are demonstrated, providing our understanding of structure formation in turbulent plasmas.

Disparate Scale Nonlinear Interactions in Edge Turbulence

Yagi

et al. 2008

Contrib. Plasma Phys.

In this topical review, we explain the recent achievement in the study of nonlinear interactions, putting an emphasis on the relevance to edge turbulence. First, we start from the survey of the essence in the nonlinear theory of drift wave -zonal flows systems, and visit the experimental observations of the nonlinear interactions of tokamak edge turbulence. Secondly, the universality of intermittent convective transport in the SOL of different magnetic devices are shown. Then, we discuss evolution of collisional drift wave instability in the linear plasma configuration, which is bounded by end plates having analogy to SOL plasmas. By introducing the Numerical Linear Device, the intermittent evolution of large-amplitude instabilities, generation mechanism of the poloidal flow and other nonlinear process are examined.