Stabilization of Ion-Temperature-Gradient–Driven Tokamak Modes by 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) modes 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. Since excellent transport properties have been observed in high ${\beta }_p$ (poloidal beta) tokamak experiments, we conjecture, as a result of our simulations, that this may be due to the stabilization of ITG modes by the reduction of the $▽B$ drifts.