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A method has been proposed to study heat transport in magnetically confinement plasmas, based on the transfer entropy (TE). In this work, we study this method by introducing perturbations in simulations made using a resistive Magneto-HydroDynamic model. The evolution of radial heat transport is monitored using the TE, and these results are used to compute an effective heat diffusivity. This effective diffusivity is then compared to estimates from other methods. The analysis is applied to several numerical simulations and in various radial ranges. It is shown that the transfer entropy is a suitable technique to analyze heat transport and evaluate an effective diffusivity in fusion plasmas. [ABSTRACT FROM AUTHOR]

It is shown that the statistical and correlation properties of the local turbulent flux measured at different radial locations of the cold, weakly ionized plasmas inside the Santander Linear Plasma Machine [Castellanos et al., Plasma Phys. Control. Fusion 47, 2067 (2005)] are consistent with diffusive-like transport dynamics. This is in contrast to the dynamical behavior inferred from similar measurements taken in hotter, fully ionized tokamak and stellarator edge plasmas, in which longterm correlations and other features characteristic of complex, non-diffusive transport dynamics have been reported in the past. These results may shed some light on a recent controversy regarding the possible universality of the dynamics of turbulent transport in magnetized plasmas. [ABSTRACT FROM AUTHOR]

In this work, the radial transport of tracers in an H-mode run in the CUTIE code [A. Thyagaraja et al., Phys. Plasmas 12, 090907 (2005)] is analyzed globally. Several techniques are applied to the study of the trajectories performed by the tracers, measuring the degree of self-similarity in the motion and searching for long range spatial and temporal correlations. The results are compared to those of an L-mode run [G. Sánchez Burillo et al., Phys. Plasmas 16, 042319 (2009)] in order to highlight the changes between L and H. The analysis of self-similarity parameters of the motion reveals that changes, if any, are slight, although the reliability of the results is limited. Nevertheless, the study of the mean step size indicates that transport is more local (or rather less global) and the anomalous diffusion contribution is less dominant. Namely, the variance of the radial distribution of tracers is smaller in H-mode and the strong asymmetry in the positive/negative steps performed by the tracers vanishes. [ABSTRACT FROM AUTHOR]

Transport models for tokamak devices are often based on transport coefficients involving a critical threshold condition. In this paper, it is argued that the validation of such models against experimental data requires special care when the system profiles are close to this threshold (at some locations), due to the contribution of fluctuations to transport. The arguments presented here could have implications for the understanding and modeling of heat transport in tokamaks, since the large stiffness of the temperature profile observed in experimental points to a near-critical situation over much of the radius. The difficulties are illustrated by means of a simplified transport model, and a possible way to ameliorate this issue is proposed. [ABSTRACT FROM AUTHOR]

Plasma density fluctuations and electrostatic turbulent fluxes measured at the scrape-off layer of the Alcator C-Mod tokamak [B. LaBombard, R. L. Boivin, M. Greenwald, J. Hughes, B. Lipschultz, D. Mossessian, C. S. Pitcher, J. L. Terry, and S. J. Zweben, Phys. Plasmas 8, 2107 (2001)], the Wendelstein 7-Advanced Stellarator [H. Renner, E. Anabitarte, E. Ascasibar et al., Plasma Phys. Controlled Fusion 31, 1579 (1989)], and the TJ-II stellarator [C. Alejaldre, J. Alonso, J. Botija et al., Fusion Technol. 17, 131 (1990)] are shown to obey a non-Gaussian but apparently universal (i.e., not dependent on device and discharge parameters) probability density distribution (pdf). The fact that a specific shape acts as an attractor for the pdf seems to suggest that emergent behavior and self-regulation are relevant concepts for these fluctuations. This shape is closely similar to the so-called Bramwell, Holdsworth, and Pinton distribution, which does not have any free parameters. [ABSTRACT FROM AUTHOR]

Profile consistency is a long-standing mystery of transport in thermonuclear fusion plasmas. This phenomenon is critically tested by studying the system response to off-axis fueling or heating. The present paper investigates the potential of a recently proposed probabilistic transport model to simulate this phenomenon, and it is found that most of the observed phenomenology can be reproduced, at least qualitatively. In particular, the observed differences between tokamaks and stellarators under off-axis heating may find an explanation in this framework. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Microwave scattering diagnostics are described that allow direct measurements of the turbulent processes in the high-temperature plasma of magnetic confinement systems. The first physical results are presented from fluctuation measurements carried out in 2000-2001 in three stellarators: L-2M (Institute of General Physics, Moscow), LHD (National Institute of Fusion Science, Toki), and TJ-II (CIEMAT, Madrid). Plasma density fluctuations in the axial (heating) regions of the L-2M and LHD stellarators were measured from microwave scattering at the fundamental harmonic of the heating gyrotron radiation. In the TJ-II stellarator, a separate 2-mm microwave source was used to produce a probing beam; the measurements were performed at the middle of the plasma radius. Characteristic features of fluctuations, common for all three devices, are revealed by the methods of statistical and spectral analysis. These features are the wide frequency Fourier and wavelet spectra, autocorrelation functions with slowly decreasing tails, and non-Gaussian probability distributions of the magnitudes and the increments in the magnitude of fluctuations. Observations showed the high level of coherence between turbulent fluctuations in the central region and at the edge of the L-2M plasma. The drift-dissipative instability and the instability driven by trapped electrons are examined as possible sources of turbulence in a high-temperature plasma. [ABSTRACT FROM AUTHOR]

The statistical properties of plasma fluctuations have been investigated in the plasma boundary region of fusion (tokamaks and stellarators) and nonfusion plasmas. Fluctuations in ion saturation current and floating potential have a near-Gaussian character in the proximity of the velocity shear layer (r[sub sh]). However, fluctuations deviate from a Gaussian distribution when moving inside of the plasma edge (rr[sub sh]). Furthermore, fluctuations show sporadic pulses that are asymmetric in time. The present analysis shows a coupling of those pulses and the averaged flow in the shear layer region. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The results of an experiment show that in the edge plasma of a L-2M stellarator the radial electric field is one of the determining factors influencing the formation of spatial structures and fluctuational particle fluxes. A point where the poloidal velocity of the fluctuations reverses is observed in an experiment with a high neutral-gas flux from the chamber walls. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Results are reported from an experimental study of the characteristics of the turbulent edge plasma in the L-2M stellarator. Extended coherent structures are observed to form in the poloidal direction. The poloidal coherence length of the fluctuations reaches 20 cm. The coherence of the fluctuations depends appreciably on the poloidal azimuth and is maximum along the outer edge, as is natural for unstable modes in a toroidal plasma. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Focuses on the statistical properties of plasma fluctuations and induced particle flux in the TJ-I tokamak and TJ-IU torsatron. Finding that Gaussian fluctuations induce bursty turbulent fluxes; Experimental setup for the measurement of turbulent flux; Variation of the local flux probability distribution function with radial position.

Plasma edge fluctuations show a degree of intermittency similar to fluid turbulence. Using fluctuation measurements obtained with Langmuir probe data from two confinement devices, it is shown that plasma fluctuations have a multifractal character over the fluctuation range of scales with intermittency levels comparable to the levels measured in neutral fluid turbulence. In the mesoscale range, that is, for time scales between 10 times the turbulence decorrelation time and plasma confinement time, plasma fluctuations have a structure closer to a monofractal with very low intermittency. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The dynamical coupling between density gradients and particle transport has been investigated using similar experimental tools in the plasma boundary of different tokamak (JET, ISTTOK) and stellarator (TJ-II) devices, showing that the size of turbulent events is minimum in the proximity of the most probable density gradient. Experimental results were found to be consistent with results from two very different models of plasma turbulence and transport. The present findings, common to several plasma devices, suggest the importance of self-regulation mechanisms between plasma transport and gradients in fusion devices. [ABSTRACT FROM AUTHOR]