Mechanism of Structure-Driven Nonlinear Instability of Double Tearing Mode in Reversed Magnetic Shear Plasmas
Mechanism of Structure-Driven Nonlinear Instability of Double Tearing Mode in Reversed Magnetic Shear Plasmas
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DOI：
10.1585/pfr.5.038
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发表时间：
2010-10
影响因子：
0.8
通讯作者：
M. Janvier;Y. Kishimoto;Jiquan Li
中科院分区：
文献类型：
--
作者：
M. Janvier;Y. Kishimoto;Jiquan Li
研究了双撕裂模式（DTM）非线性失稳的触发因素，即结构驱动的失稳导致爆炸生长和随后的崩溃。我们使用简化的MHD方程来求解准稳态非线性状态缓慢演化过程中二维磁岛变形的平衡扰动的演化。通过检查接近边际稳定性的条件（在此条件下不会触发爆炸性增长），我们已经确定了一种新的次级不稳定性，当与岛屿相关的主要波动的磁能达到临界水平时，这种不稳定性开始增长。这种不稳定性的能量来源不同于线性DTM；它起源于由dtm驱动的磁岛引起的空间变形，并负责随后的非线性失稳。这种次级不稳定性的增长率与磁能成正比，表明它具有调制特性。
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.