Study of the Mechanisms Leading to the Nonlinear Explosive Growth of Double Tearing Instabilities in Fusion Plasmas

Abstract

AbstractIn the recent decades, research in magnetic confinement fusion has intensified to achieve a better confinement of the plasmas necessary to obtain power generation. One of the solutions is the formation of internal transport barriers appearing when the magnetic shear is reversed. However, such configuration leads to current-driven instabilities such as the double tearing mode (DTM). In the present work, we study the nonlinear destabilization of the DTM occurring when the generated magnetic islands are close to each other so that the dynamics is enhanced. By choosing a configuration near marginal nonlinear stability for this nonlinear destabilization, we study the possibility for a secondary instability to be generated from the two-dimensionally deformed magnetic structure and to be a cause of the nonlinear destabilization. We find that from an equilibrium with severe deformation of islands, a new secondary instability with a large growth rate can be generated. A parametric dependency analysis shows that this new instability has the same characteristics as a modulational one.KeywordsCurrent-driven instabilityMagnetic islandsMarginal stabilityRMHDSecondary instability