[en] This workshop made it possible to gather for the first time plasma physicists, dynamical systems physicists and mathematicians, around a general theme focusing on the characterisation of chaotic transport. The participations have been divided into 4 topics: - dynamical systems and microscopic models of chaotic transport, - magnetic fluctuations and transport in tokamaks, - drift wave turbulence, self-organisation and intermittency, and - Wave-particle interactions

[en] This paper reviews some recent experimental and theoretical work on tokamak edge turbulence carried out by the IPR group. The theoretical work has been done with N. Chakrabarti, A. Das R. Singh and the experimental work with R. Jha, S.K. Mattoo, Y.C. Saxena, C. V. S. Rao and the ADITYA team. (author)

[en] The calculation of incremental transport of particles and heat beyond the test-particle or quasilinear approximation has been performed by Thoul, Similon and Sudan^1,2,3 employing Kraichnan's direct interaction approximation. The resulting transport matrix is found to violate Onsager's principle. An attempt to explain this violation in terms of the non-thermal electric field fluctuation spectrum is presented. (author)

[en] Recently, a numerical work analyzed the effect of the separatrix shape on stochasticity onset on a two-wave Hamiltonian system and more particularly the dependence of the stochasticity threshold on the separatrix angle at the hyperbolic fixed point. The conclusion of this work was that the flattering of this angle has a very significant effect in the reduction of the stochasticity threshold. That means that a bifurcation from hyperbolicity to parabolicity increases the chaotic transport. Using this result, the authors proposed a scenario to the unresolved problem of internal disruptions in tokamaks, relating the catastrophic behavior observed during those disruptions to the flattening of the separatrix angle at the hyperbolic fixed point. (authors)

[en] Anomalous kinetics of particles has been studied in real systems with Hamiltonian chaos. Such systems have fractal sets of islands or tori (cylinders) in the phase space. These sets are responsible for the anomalous kinetics. Different examples for plasmas and fluids are given to support this statement and to explain its origin. Fractional kinetic equation has been derived for the anomalous transport problem and Renormalization Group approach has been developed to get a critical exponent of transport. (author)

[en] While computer simulations of drift wave turbulence clearly show regimes dominated by coherent vortex structures, the experimental evidence for the existence of such regimes is inconclusive. Two experimental searches on TEXT-U for coherent structures yield mixed results. One study uses a conditional statistical analysis of the plasma fluctuations to select candidate structures and finds evidence. A second study uses the bi-spectral analysis to identify phase-correlated structures and finds a structure localized to the q = 3 surface. Motivated by these experiments, we have modeled again the turbulence as a gas of vortices and waves and computed the same conditional potential structures that are reported in the experiments. The physical requirement supposed is that the amplitude of the reference signal exceed a level appropriate for vortex trapping. The important conclusion shown here, which follows from comparison of the computer simulations with the conditional analysis as applied on TEXT-U, is that since the amplitude dependence of the decay rate is sufficiently week, the conditional averaging method fails to yield conclusions on the presence of the structures. In addition the spatial sampling from the two-probe measurements averaged over a series of discharges may lack the radial resolution needed to identify coherent structures embedded in the background turbulence. (author)

[en] Plasma hydrodynamic oscillations attract much attention within the context of the problem of plasma magnetic confinement and anomalous transport phenomena. In this paper the statistical theory of convective cells and magnetic islands in magnetized plasmas is reviewed. Renormalized statistical approach is applied for the study of fluctuations and fluctuation-induced transport with regard to nonlinear interaction between fluctuations. Stationary spectral distributions of the electromagnetic field fluctuations and the coefficient of convective-cell-induced diffusion are calculated. Thermal convective cell spectrum and suppression of convective-cell-induced diffusion due to magnetic field fluctuations in the plasma of small but finite pressure are demonstrated. (authors)

[en] The qualitative features of large scale structures in the simplest case of kinetic plasma turbulence, the electron beam-plasma instability, are described. A New approach is introduced, resting on a classical mechanics technique. It starts from a N-body description of the plasma, and leads to the derivation of a set of equations describing the self-consistent evolution of Langmuir waves and near-resonant particles. (authors)

[en] Numerical and analytical investigations of the two dimensional gravitation induced Rayleigh Taylor instability are carried out to understand some recent experimental observations on the BETA device. The primary emphasis is on the study of the fluctuation statistics and the possible mechanisms of intermittency in the turbulence. (authors)

[en] The existence of small scale magnetic islands having a characteristic width of the order of the skin depth is discussed in terms of nonlinear hydrodynamic equations for a nonuniform plasma in a sheared magnetic field. A resultant electron thermal diffusivity has sensitive dependence on the electron temperature gradient, η_e. (authors)