Analysis and Control of Spontaneous Currents in Rippled Tokamak Plasmas and Helical Plasmas

在具有高等离子体压力的磁约束环面等离子体中，自发电流（称为自举电流）的流动与新古典输运理论的预测一致，它对等离子体约束有重要影响。本文从理论上探讨了自举电流对等离子体约束的影响，并探讨了控制自举电流的方法。为了精确计算非轴对称等离子体的MHD平衡，开发了三维MHD平衡程序HINT2。我们还分析了等离子体边界形状的凹凸分量对MHD稳定性的影响。在L=1的heliotron J实验中，证明了自举电流的方向可以在改变磁组态时发生反转。对L=1氦离子等离子体和脉动托卡马克等离子体的自举电流进行了理论分析，阐明了磁组态和环面场脉动对自举电流的依赖关系。采用一致的MHD平衡计算方法，对等离子体驱动电流和自举电流进行了综合模拟。为此，对分析自引导电流和束流驱动电流的数值程序进行了模块化，开发了模拟非轴对称环形等离子体中等离子体电流分布时间演变的模块。阐明了LHD等离子体实验中等离子体电流谱的瞬态响应机制。

In magnetically confined toroidal plasmas with high plasma pressure, a spontaneous current, which called the bootstrap current, flows as is predicted by the neoclassical transport theory, and it gives an significant influence on the plasma confinement. The following studies have been done in order to investigate the effects of the bootstrap current on the plasma confinement theoretically, and to consider the methods to control the bootstrap current.1. Three dimensional MHD equilibrium code, HINT2, has been developed to calculate the MHD equilibrium of non-axisymmetric plasmas accurately. We also analyze the effect of the bumpy component of the plasma boundary shape on the MHD stability.2. In the experiments of an L=1 heliotron device, Heliotron J, it is demonstrated that the direction of the bootstrap current can be reversed when the magnetic configuration is varied. We did the theoretical analysis of the bootstrap current in L=1 heliotron plasmas and in rippled tokamak plasmas, and clarified the dependence of the magnetic configuration and the toroidal field ripple on the bootstrap current.3. The integrated simulations of the plasma current profile including the beam driven current and the bootstrap current have been done with the consistent MHD equilibrium calculation. For this purpose, numerical program which analyze the bootstrap current and beam driven current has been modularized, and the module which simulate the time evolution of the plasma current profile in non-axisymmetric toroidal plasmas has been developed. We clarified the mechanism of the transient response of the plasma current profile in LHD plasma experiments.