In this paper, recent progress on experimental analysis and theoretical models for non-local transport (non-Fickian fluxes in real space) is reviewed. The non-locality in the heat and momentum transport observed in the plasma, the departures from linear flux-gradient proportionality, and externally triggered non-local transport phenomena are described in both L-mode and improved-mode plasmas. Ongoing evaluation of 'fast front' and 'intrinsically non-local' models, and their success in comparisons with experimental data, are discussed
Fast visible imaging is used on a cylindrical magnetized argon plasma produced by thermionic discharge in the Mirabelle device. To link the information collected with the camera to a physical quantity, fast camera movies of plasma structures are compared to Langmuir probe measurements. High correlation is found between light fluctuations and plasma density fluctuations. Contributions from neutral argon and ionized argon to the overall light intensity are separated by using interference filters and a light intensifier. Light emitting transitions are shown to involve a metastable neutral argon state that can be excited by thermal plasma electrons, thus explaining the good correlation between light and density fluctuations. The propagation velocity of plasma structures is calculated by adapting velocimetry methods to the fast camera movies. The resulting estimates of instantaneous propagation velocity are in agreement with former experiments. The computation of mean velocities is discussed.
Fluctuation-induced cross-field convective particle flux is studied in the cylindrical magnetized plasma assembly for non-linear turbulence analysis (PANTA). The plasma presents a wave turbulence characterized by a limited number of developing modes. To study the link between mode dynamics and particle transport, frequency-dependent time evolution of transport is obtained by applying complex continuous wavelet decomposition on spatio-temporal data from electrostatic probes. The method is shown to recover transport description consistent with other analysis methods for a weakly turbulent state. For a plasma state featuring a large non-sinusoidal structure, the time evolution of transport on the second harmonic of the main fluctuation shows a slow modulation of azimuthal mode number m = 0 with similarities to a zonal perturbation.
A solitary drift wave structure and its quasi-periodic change are discovered in a linear magnetized plasma. Detailed investigations show that the periodic changes are accompanied by an emission of splash, that is, a short lifetime event characterized by much higher frequencies than that of the fundamental drift waves. Dynamic interaction between the solitary wave and zonal flows is found to cause the emission of splashes since the splashes occur in a particular phase of zonal flows. The findings should give a deep insight into the dynamics and structural formation of magnetically confined plasmas and rotating planets, which are governed by drift and Rossby waves, respectively.
The competing effects of the long-range fluctuation, which has been found on LHD [1], on thef net turbulent transport are discussed. The transport, which is driven directly by this mode, is evaluated. Then, the associated reduction of fluctuations in the range of drift wave turbulence is analyzed, by employing the predator prey model. The transport driven by microscopic turbulence is reduced by the appearance of long-range fluctuations. Comparing these two competing processes, the condition is derived for the net transport to be reduced by the appearance of this long-range fluctuation. In addition, the experimental observations of microscopic fluctuations are discussed. The reduction of high-frequency fluctuations occurs in conjunction with the long-range fluctuations.
An open-loop spatiotemporal synchronization method is applied to flute modes in a cylindrical magnetized plasma. It is demonstrated that synchronization can be achieved only if the exciter signal rotates in the same direction as the propagating mode. Moreover, the efficiency of the synchronization is shown to depend on the radial properties of the instability under consideration. It is also demonstrated that the control disposition can alternatively be used to produce strongly developed turbulence of drift waves or flute instabilities.
This paper presents full cross-section measurements of drift waves in the linear magnetized plasma of the Mirabelle device. Drift wave modes are studied in regimes of weakly developed turbulence. The drift wave modes develop azimuthal space-time structures of plasma density, plasma potential, and visible light fluctuations. A fast camera diagnostic is used to record visible light fluctuations of the plasma column in an azimuthal cross section with a temporal resolution of 10 μs corresponding approximately to 10% of the typical drift wave period. Mode coupling and drift wave dispersion are studied by spatiotemporal Fourier decomposition of the camera frames. The observed coupling between modes is compared to calculations of nonlinearly coupled oscillators described by the Kuramoto model.
Non-Gaussian statistical properties of the azimuthally averaged momentum and particle fluxes driven by turbulence have been simultaneously observed in inhomogeneous magnetized plasmas for the first time. We identified the stretched Gaussian distribution of the both fluxes and the transition from the point-wise distribution to averaged ones was confirmed. The change of the particle flux precedes that of the momentum flux, demonstrating that the momentum flux is induced by the relaxation of density gradient.
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