Bifurcations and transport barriers in the resistive-g paradigm

The so-called resistive-g (resistive pressure-gradient-driven turbulence) p aradigm is a widely accepted and frequently investigated model for nonlinea r plasma dynamics. The parameter dependences of the generated transport bar riers as well as third order bifurcations will be discussed numerically and analytically in the present paper. First, using a Galerkin representation, bifurcating states (from the conductive states in a rectangular cell) are investigated for the cases when only one unstable mode dominates. The depen dence of the bifurcation properties on the aspect ratio of the domain is di scussed, leading to the conclusion that for vanishing (or small) magnetic s hear the so-called low, high, and edge localized mode transitions do not oc cur for small aspect ratios of the domain. Including reasonable magnetic sh eer, the small-aspect-ratio cutoff disappears, and transport barriers may e xist in a broad parameter range. Second, for small aspect ratios, interesti ng codimension-2 bifurcations occur. When unfolding the dynamics up to thir d order, e.g., a weakly nonlinear interaction of convection cells is observ ed. The analytical results are confirmed by numerical simulations.