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Structure Change in Toroidal Plasma Due to Nonlinear Evolution of Pressure Driven Mode

压力驱动模式的非线性演化导致环形等离子体的结构变化

基本信息

批准号：
13680572
负责人：
ICHIGUCHI Katsuji
金额：
$ 2.05万
依托单位：
National Institute for Fusion Science
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2001
资助国家：
日本
起止时间：
2001 至 2004
项目状态：
已结题

项目摘要

The comprehensive understanding of the MHD stability of the toroidal plasma has been aimed in the view point of the structure change in the profiles of pressure and the magnetic configuration induced in the nonlinear evolution of the pressure driven mode. The heliotron plasma is focused because the interchange mode is the most dangerous instability. Particularly, in the LHD experiments, good confinement is observed in the region linearly unstable for the interchange mode, and therefore, the stabilizing mechanism is pursued.In order to carry out the analysis, a nonlinear numerical code, NORM, is developed based on the reduced MHD equations. At first, the nonlinear evolution of a low beta plasma which is slightly unstable for the linear ideal interchange mode is examined In this case, the mode is saturated mildly without any disruptive phenomenon. The pressure profile has local flat regions around the resonant surfaces. This structure change reduces the driving force and leads to the mild saturation. Next, the nonlinear evolution of the plasma with the same pressure profile and high beta value is examined. In this case, a disruptive phenomenon is obtained. This is because the enhancement of the driving force causes an overlap of the vortices. However, since the pressure profile has to change continuously in the actual experiments, the plasma with the saturated pressure profile at the lower beta value and the high beta value is examined. In this case, the plasma is saturated without the disruptive phenomenon. These results indicate that the LHD plasma is self-organized so that the stable pressure profile can be achieved in the increase of the beta value.When the local flat region is generated in the pressure profile, the magnetic islands are generated simultaneously. The generation is attributed to the driven reconnection which is induced by the vortices of the interchange mode. The number of the islands is twice of the poloidal mode number of the driving mode.

从压力驱动模的非线性演化引起的压力和磁位形的结构变化的角度对环形等离子体的MHD稳定性有了全面的认识。由于交换模是最危险的不稳定性，因此对日光管等离子体进行了重点研究。特别地，在LHD实验中，在交换模线性不稳定的区域观察到了良好的约束，因此，为了进行分析，我们开发了一个基于简化MHD方程的非线性数值程序NORM。本文首先研究了低β等离子体的非线性演化，它对于线性理想交换模是轻微不稳定的，在这种情况下，模是温和饱和的，没有任何破坏现象。压力分布在谐振表面周围具有局部平坦区域。这种结构变化降低了驱动力，导致了温和的饱和。接下来，研究了具有相同压力分布和高β值的等离子体的非线性演化。在这种情况下，获得了破坏性现象。这是因为驱动力的增强导致涡旋的重叠。然而，由于压力分布在实际实验中必须连续变化，因此检查了在低β值和高β值处具有饱和压力分布的等离子体。在这种情况下，等离子体饱和，没有破坏现象。这些结果表明，LHD等离子体是自组织的，随着β值的增加，可以获得稳定的压力分布，当压力分布中产生局部平坦区域时，同时产生磁岛。这一现象的产生是由于交换模中的涡旋引起的驱动重联。岛的数量是驱动模式的极向模式数量的两倍。