HIGH SPEED PARALLEL COMPUTATION OF THREE-DIMENSIONAL EQUILIBRIUM AND STABILITY FOR NONAXISYMMETRIC TORUS PLASMAS

1.用我们开发的三维平衡程序HINT研究了几种典型的螺旋等离子体结构，即Heliotron/Torsatron、Helias和Heliac的平衡特性。我们发现：（1）在某些构型中，压力驱动的岛可以发生“自愈合”;（2）即使在不稳定的等离子体构型中，压力驱动的岛也会发生“自愈合”;（3）因此，等离子体电流的全局效应被证明是岛形成的重要物理机制;（4）在某些情况下，非共振型不稳定性的激发会显著改变螺旋平衡的结构.为了研究压力驱动不稳定性引起的等离子体自组织现象是否会发生，开发了一个新的非轴对称环形等离子体非线性模拟程序。所开发的程序的主要特点是在全三维几何中求解全MHD方程的时间发展。这样的非线性模拟很少尝试到目前为止。我们已经执行了模拟，并发现，虽然在发展的初始阶段的不稳定性的行为与线性分析的预测一致，强模式耦合最终被激发为不稳定性的非线性发展，这导致过渡到一个强烈的湍流状态。有趣的是，在后期，等离子体压力分布变宽，等离子体自发地变得安静。在并行计算机上开发的代码的效率进行了研究。保持通过介质作用的物理原理的形式的算法被发现是有效的。找到了几种使大规模仿真代码有效利用CPU的实用方法。

1. Equilibrium ptoperties of several typical configurations of helical plasmas, namely, heliotron/torsatron, Helias, and Heliac, were studied by using the 3D equilibrium code HINT,which we have developed. We found (1) in some configurations, a self-healing' of pressure driven islands can occur, (2) it occurs even in an unstable plasma configuration, (3) therefore global effects of plasma currents are proved to be important as a physical mechanism of island formation, and (4) in some cases, excitation of nonresonant type instability modifies structure of helical equilibria significantly.2. A new nonlinrear simulation code for nonaxisymmetric torus plasmas were successfully developed with a motivation to clarify whether or not self-organization of a plasma which is induced by pressure-driven instabilities can occur. The main characteristics of the developed code are that time development of the full MHD equations are solved in a full three dimensional geometry. Such a nonlinear simulation has seldom been attempted so far. We have executed simulations and found that while behavior of instabilities in an initial phase of the development agrees well with predictions of linear analyzes, strong mode coupling is eventually excited as the nonlinear development of instabilities, which results in a transition to a strongly turbulent state. It's interesting to note that in a later stage, the plasma pressure profile is broadened and the plasma spontaneously becomes quiet.3. Efficiency of the developed codes on a parallel computer was investigated. Algorithm that keeps the form of the physics principle of action through medium was found to be effective. Several practical methods which enable large scale simulation codes to use CPUs efficiently were found.