Gyrokinetic simulations of double tearing modes in toroidal plasma

An investigation of the characteristics of double-tearing modes (DTMs) and the influence of the kinetic effects of ions has been carried out with the gyrokinetic code GTC. A simplified linear fluid and a gyrokinetic model has been used for the electron and ion dynamics, respectively. It was found that as the separation of the rational surfaces was increased, the growth rates of DTMs were enhanced and the DTM system tended to decouple into a system of two single-tearing modes. When the width between the rational surfaces is larger, the corresponding amplitude of the inner-tearing mode is smaller. We also demonstrate that the existence of thermal ions destabilizes the DTM. The toroidal effect also has a mild destabilizing effect (similar to 8%) on the growth of DTMs, which is consistent with the theoretical analysis. (C) 2021 Elsevier B.V. All rights reserved.