Plasma and Fusion Research
Online ISSN : 1880-6821
ISSN-L : 1880-6821
Rapid Communications
Mechanism of Structure-Driven Nonlinear Instability of Double Tearing Mode in Reversed Magnetic Shear Plasmas
Miho JANVIERYasuaki KISHIMOTOJiquan LI
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2010 Volume 5 Pages 038

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Abstract

The trigger for the nonlinear destabilization of the double tearing mode (DTM), referred to as a structure-driven instability leading to explosive growth and subsequent collapse, is investigated. We use the reduced MHD equations that solve the evolution of perturbations from an equilibrium deformed by two-dimensional magnetic islands during the slow evolution of the quasi-steady nonlinear regime. By examining conditions near marginal stability (under which the explosive growth is not triggered), we have identified a new secondary instability that starts growing when the magnetic energy of the primary fluctuations associated with the islands reaches a critical level. The energy source of this instability is different from that of the linear DTM; it originates in the spatial deformation due to the DTM-driven magnetic islands and is responsible for the subsequent nonlinear destabilization. The growth rate of this secondary instability is found to be proportional to the magnetic energy, suggesting that it exhibits modulational characteristics.

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© 2010 by The Japan Society of Plasma Science and Nuclear Fusion Research
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