The ExB transport in magnetized plasmas is strongly influenced by particle trapping in the structure of the stochastic potential. This process appears in low frequency turbulence characterized by Kubo numbers K higher than one. It determines the decrease of the diffusion coefficient and the modification of its scaling law in the parameters of the turbulence. This trapping process was studied by developing a new statistical approach, the decorrelation trajectory method [1].
We present here a detailed study of the effect of the spectrum of the turbulence on the transport. It is already known that in the quasilinear case corresponding to K<1 the shape of the spectrum does not influence the asymptotic diffusion coefficient D. Only the average wave number appears in the expression of D. We show that at K>1 the shape of the spectrum has a strong influence on the diffusion coefficient. This is a nonlinear effect produced by trajectory trapping that changes the expression of D. The asymptotic diffusion coefficient scales in this case as K at a power γ, which depends on the turbulence spectrum. The values of γ are in the interval (0, 1). The upper limit corresponds to the absence of trapping and is the well-known Bohm diffusion coefficient. The lower limit corresponds to total trapping. The value of γ inside this interval depends on the wave number spectrum of the turbulence. More precisely, the value of γ is determined by the asymptotic space dependence of the Eulerian correlation of the stochastic potential E(x). Since E(x) is the Fourier transform of the spectrum, our results show that the small wave number components of the spectrum have a strong effect on the diffusion coefficient.
A fast and precise code for determining the time dependent diffusion coefficient for given spectrum of the turbulence was developed. It can be used as a tool in the analysis of the experimental data.

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