Formation and Stability of Oblate Field-Reversed Configuration Plasmas

通过控制负偏置θ箍缩（FRTP）约束场的镜比和磁场指数，形成了扁圆场反转位形（FRC）。当镜比（1.8）和场折射率（0.3）增大时，FRC等离子体的伸长减小到小于2.5。场折射率可以调节径向内爆强度和轴向收缩.利用FRTP的反射镜和尖形偏置场，研究了FRC等离子体的n=1模运动.在前一种偏置配置中，n=1的运动达到等离子体半径的20-40%，尽管在后一种配置中它是低水平的。实验证实了多极场可以控制n=1的剧烈运动。理论上推导了一个将等离子体推回到平衡位置所需的临界强度，并与实验结果进行了比较。两个值在实验重现性范围内一致。其临界场强要求约为约束场的15%。发现n=2的转动不稳定性也可以用同样的阶数稳定化，对n=1的运动、等离子体形状和等离子体内部结构的诊断也是一个新的发展。光学诊断是为n=1的运动。改进了一种利用抗磁测量诊断等离子体形状的方法。结果表明，等离子体形状可以通过迭代求解Grad-Shafranov方程来确定。边界条件是测量的磁通量和磁场强度。初始值是抗磁方法的等离子体形状。采用快速选通像增强器的CCD摄像机可以观察等离子体截面

An oblate field-reversed configuration (FRC) is formed by a control of a mirror ratio and a magnetic field index of the confinement field of a negative biased theta-pinch (FRTP). An elongation of FRC plasmas decreases less than about 2.5 by the increase of the mirror ratio (1.8) and the field index (0.3). The field index is possible to contribute to the adjustment of a radial implosion strength and an axial contraction.An n=1 mode motion of FRC plasmas is investigated by using a mirror and a cusp configuration of the bias field of the FRTP. The n=1 motion reaches 20-40% of the plasma radius in the former bias configuration, although it is a low level in the latter configuration. It is experimentally confirmed that the violent n=1 motion can be controlled by a multipole field. A critical strength needed to push back the plasma to the equilibrium position is theoretically derived by using a simple model including a conductor effect of the wall and is compared with the experimental results. Both values agree within the experimental reproducibility. The critical field strength of which is required to be about 15% of the confinement field. It is found that the n=2 rotational instability can also be stabilized by the same order.Several diagnostics for the n=1 motion, a plasma shape and an internal plasma structure are a newly developed. Optical diagnostics is developed for the n=1 motion. A plasma shape diagnostic by a diamagnetic measurement is improved. It is found that the plasma shape can be determined by solving a Grad-Shafranov equation iteratively. The boundary condition is the measured magnetic flux and magnetic field strength. The initial value is the plasma shape of the diamagnetic method. A plasma cross-sectional view can be observed by a CCD camera with fast-gated image intensifier