Self organized formation and sustainment of helicity-driven spherical high beta torus plasmas

在螺旋度注入球环装置中，通过对球环等离子体内部磁场的测量，揭示了同轴螺旋度注入（CHI）维持的球环（ST）等离子体内部磁场和电流密度结构。由CHI形成的ST等离子体的内部磁位形与数值平衡拟合计算的结果符合得很好。ST的闭合极向磁通的产生已被验证通过改变在同一设备中的外部环向场强度。为了理解螺旋驱动系统中的自组织，我们研究了低纵横比环形等离子体的动力学，通过减小外部环形场并在时间上反转其符号。因此，我们已经发现，螺旋驱动的环形等离子体弛豫向翻转状态。令人惊讶的是，它已被观察到，不仅环向通量，而且极向通量反转符号自发在松弛过程中。日 ...更多信息 磁场的自反转归因于中心开磁通的n1扭结不稳定性的非线性增长。采用三维磁流体动力学（MHD）数值模拟方法研究了螺旋驱动球马克等离子体的动力学行为。结果表明，环形电流是由连续的等离子体团注入驱动的，并伴随着中心开磁通柱的n=1振荡。从同轴螺旋度注入（CHI）电流驱动的观点来看，由闭合通量面组成的翻转ST（F-ST）等离子体可以与正常ST相媲美，我们还研究了F-ST等离子体的维持机制。螺旋度驱动的弛豫理论表明，在保流器中存在ST和F-ST的混合态。螺旋度通过ST与枪电极耦合转移到F-ST。结果表明，环向磁场之间的磁重联对F-ST的维持起着重要作用，外边缘区域的磁场呈现出规则的振荡，振荡的n=1模振幅较大。F-ST的核心区域似乎相对稳定。少

In the Helicity Injected Spherical Torus device, internal magnetic field and current density structures of spherical torus (ST) plasmas sustained by coaxial helicity injection (CHI) have been revealed via intensive internal magnetic measurements. The internal magnetic configuration of the ST plasma formed by CHI is in good agreement with the results of numerical equilibrium fitting calculations. The generation of closed poloidal flux of ST has been verified by varying the external toroidal field strength in the same device. In order to understand self-organization in helicity-driven systems, we have investigated the dynamics of low-aspect-ratio toroidal plasmas by decreasing the external toroidal field and reversing its sign in time. Consequently, we have discovered that the helicity-driven toroidal plasma relaxes towards the flipped state. Surprisingly, it has been observed that not only toroidal flux but also poloidal flux reverses sign spontaneously during the relaxation process. Th … More e self-reversal of the magnetic fields is attributed to the nonlinear growth of the n 1 kink instability of the central open flux. The dynamics of helicity-driven spheromak plasmas has been investigated using three-dimensional magnetohydrodynamic (MHD) numerical simulations. It is found that the toroidal current is driven by continuous plasmoid injection accompanied by the n=1 oscillation of central open flux column. Also, we propose that the pulse injection of the helicity is effective for suppressing the n=1 fluctuation.From the viewpoint of coaxial helicity injection (CHI) current drive, it is conceivable that the flipped ST (F-ST), which consists of only closed flux surfaces, compares favorably with the normal ST. We have investigated the sustainment mechanism of the F-ST plasma. The helicity-driven relaxed theory shows that there exist the mixed states of ST and F-ST in the flux conserver. Helicity is transferred to F-ST through the ST with coupling with gun electrodes. It has been found that magnetic reconnection between the toroidal magnetic field plays important role in the sustainment of the F-ST. The magnetic field in the outer edge region shows regular oscillations which have a large amplitude of the n=1 mode. The core region of the F-ST seems to be relatively stable. Less