Dynamic behavior of structure trnsition phenomena in nonequilibrium and nonlinear plasmas in open systems

对球形托卡马克和螺旋等离子体中的弛豫现象进行了非线性MHD模拟，包括三维提示平衡计算。揭示了球形托卡马克中整体弛豫现象的动力学。分析了锯齿波和内部重联事件。对于锯齿形情况，发现了一种新的非线性触发机制，在这种机制中，核心区的n=1活动随后被外围区更高的n个气球模的发展所激发。在压力崩溃过程后，环面返回到接近轴对称初始构型的状态，但具有更宽的压力分布。圆环曲面的整体形状在整个事件过程中不会更改。另一方面，IRE的模拟显示环面有很大的扭曲。这些差异只是由于初始配置文件中的微小差异造成的。3D平衡代码提示不假定磁性表面的存在，在几个方向上进行了修改以扩展函数。开发了一种新的螺旋等离子体全三维MHD模拟程序。在LHD组态中观察到了由压力驱动不稳定性驱动的弛豫现象，这种松弛现象并不是破坏性的，但导致了向新的平衡的转变。等离子体形变的初始阶段是由中n阻性气球不稳定性主导的。在后期，通过自发演化到更宽的压力剖面，恢复了良好的受限状态。虚拟现实显示系统是为理解复杂现象而发展起来的一种先进的可视化手段。

Nonlinear MHD simulations on relaxation phenomena in spherical tokamak and helical plasmas, including 3D HINT equilibrium computations, are executed. The dynamics of global relaxation phenomena in spherical tokamak have been revealed. We analyze the sawtooth and the internal reconnection event (IRE). For the sawtooth case, a new nonlinear trigger mechanism is found, in which the n=1 activity in the core region is subsequently excited by development of higher n ballooning modes in the periphery region. After a process of pressure collapse, the torus returns to a state close to the axisymmetric initial configuration but with a broader pressure profile. The overall shape of the torus surface does not change throughout the event. On the other hand, simulations for IRE show a large distortion of the torus. The differences arise from only slight discrepancies in the initial profiles. The 3D equilibrium code HINT, which does not assume the existence of magnetic surfaces, is modified in a couple of directions to extend the functions. A new MHD simulation code for a full three dimensional geometry of helical plasmas were developed. A relaxation phenomenon driven by pressure driven instabilities in the LHD configuration was observed, which was not destructive but caused transition to a new equilibrium. An initial phase of plasma deformations is dominated by medium-n resistive ballooning instability. In the later stage, a well-confined state is recovered by having spontaneous evolution to a broader pressure profile. Virtual reality display system was developed as an advanced visualization method to understand complex phenomena.