Interaction between external and intrinsic torque and its impact on internal transport barrier formation: A gyrofluid simulation study

Abstract

We present a computational study of the external-intrinsic torque interaction and its impact on internal transport barrier (ITB) formation. Global flux-driven gyrofluid simulations are performed. The application of an external torque is found to facilitate or hinder ITB formation, depending on its sign relative to the direction of the intrinsic torque, which confirms a recent theoretical prediction. Simulations also show that a strong external-intrinsic torque interaction causes a cancellation of the core intrinsic rotation and subsequent ITB annihilation when an external torque counter to, and approximately equal in magnitude to, the intrinsic torque is applied to the plasma. The nullification of the intrinsic rotation in ITB is shown to be due to a cancellation of the ∇V‖ (V‖: parallel flow) contribution to the total E × B shearing rate.