Gyrokinetic Simulation of Kinetic Ballooning Mode and its Parametric Stabilization in Tokamak Plasmas With Impurities

Abstract

Kinetic ballooning mode (KBM) and its parametric stabilization in tokamaks are studied qualitatively by means of gyrokinetic simulation. The circular magnetic tokamak discharge with the Shafranov shift is considered and the $\hat {s}-\alpha $ model equilibrium is employed. The kinetic characteristics of ions, such as Landau resonance, magnetic drift, and finite Larmor radius (FLR) are all taken into account. The full ion transit and toroidal drift effects are retained. Impurity effect is also included. As a result, the existence of, and approaching way to the second KBM stable regime were identified. It was first revealed that impurities play a role of stabilizing when the impurity density profile peaks in the same direction as those of the electron and main ion density profiles, owing to that compressibility effects is weakened. It shows that the mode maximum growth rate appears at the turning point of magnetic shear $\hat {s}_{c} =q /4-q/2$ , while the formula can be modified due to other plasma parameters such as $\eta _{i}$ and impurity species. Some parametric stabilizations of KBM are suggested, including the accumulation of impurities toward the plasma center; and entering or approaching to the second stable regime by means of making the electron density or ion/electron temperature gradients high enough, by which the internal or edge transport barrier (ITB/ETB) is anticipated to be formed in many cases. In addition, we showed that the artificial control of safety factor and magnetic shear was also beneficial to the stabilization of ballooning mode.