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(TH/P1-17) Nonlinear Diffusion Regimes in Stochastic Magnetic Fields

M. Vlad1), F. Spineanu1)2), J.H. Misguich2), R. Balescu3)
1) Association Euratom - NASTI (MER) Romania, National Institute of Laser Plasma and Radiation Physics, Bucharest, Romania
2) Association Euratom - CEA sur la Fusion, CEA-Cadarache, France
3) Association Euratom - Etat Belge sur la Fusion, Université Libre de Bruxelles, Belgium

Abstract.  The problem of anomalous transport induced by the presence of a stochastic magnetic field in a tokamak plasma is studied in the frame of test particle approach. Particle collisions are taken into account together with the nonlinearity determined by the finite perpendicular correlation length of the stochastic magnetic field. The latter leads to the dynamical trapping of the magnetic lines, which are constrained to wind around stochastic magnetic islands. Using the decorrelation trajectory method we have determined the effective running diffusion coefficient for given parameters of the stochastic magnetic field and of the collisional diffusion along and across the confining magnetic field. We have shown that the interaction of particle collisions with magnetic line trapping determines a new anomalous transport regime in which the increase of particle cross-field collisional diffusion leads to the decrease of the effective diffusion coefficient.

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IAEA 2003