The formation of internal transport barriers in thevicinity of rational magneticsurfaces in tokamaks with braided magnetic fields is studied for a simplifiedmodel of the perturbed magnetic field with a broad spatial spectrumand a monotonous shear profile. Theisland overlap criterion is used to derive a condition for barrier formation.This conditionlinks the amplitude and the spectral width of the perturbation with theshear parameter.Numerical experiments with the MHD Monte-Carlo code E3D,where the problem of plasma heat conductivity is solved in 3D,confirm this formation of transport barriersin the case of a monotonous shear profile.Assuming that experimentally observed electron internal transportbarriers are the result of local reduction of electron heat transportdue to the magnetic field braiding, the amplitude and spectral widthof magnetic perturbations are estimated for the tokamak RTP.
Influence of the resonant magnetic perturbations on transport in the Large Helical Device