ITG-free tokamak configurations with magnetic field gradient reversal

Global gyrokinetic particle simulations have been used to search tokamak configurations which are stable against the Ion Temperature Gradient-driven (ITG) mode commonly held responsible for the core anomalous ion heat transport. The stable configurations are characterized by strongly reduced or reversed ∇B drifts on the low-field side. As in high βp (poloidal beta) tokamak experiments excellent transport properties have been observed, we conjecture, inspired by our simulations, that this may be the result of the stabilization of ITG modes by the reduction of the ∇B drifts. (author) 3 figs., 26 refs