Abstract
The formation of an internal transport barrier (ITB) in a tokamak plasma due to the stabilization of ion temperature gradient (ITG) driven turbulence is analyzed using a three-dimensional turbulence code [Garbet et al., Phys. Plasmas 8, 2793 (2001)]. Two mechanisms leading to a reduction of turbulent transport are studied. First, a bifurcation to an improved confinement state obtained by increasing the heating power above a threshold value with a monotonic q profile is presented. This bifurcation occurs due to a spontaneous increase of self-generated E×B rotation shear. Then, the effect of low and negative magnetic shear on the ITG driven turbulence and transport is studied. The beneficial effects of low order minimum safety factor and low curvature of the safety factor profile are shown in these simulations by varying the magnetic configuration in a large range. The evolution of the statistical properties of turbulence during the ITB formation is presented.
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