Formation of Field Reversed Configuration Plasma with Toroidal Magnetic Field

提出了利用轴向电流形成具有环向磁场的场反转等离子体的方法。利用NUCTE-3研究了轴向电流和阈值对FRC成功形成和约束的影响。检测了轴向电流的不同频率（<=4.7x10^5rad/s）和幅值（<=6OkA）。在形成阶段，澄清了两种效应；(1)在偏置场中加热嵌入等离子体(2)放大偏置通量。在约束阶段，阐明了旋转失稳的稳定化作用。虽然扭结不稳定性是由两相较大的轴向电流激发的，但证实了交流电可以避免扭结不稳定性。形成相的阈值似乎与FRC形成的极向通量限制以及预热等离子体和偏置场的干扰有关。稳定电流值与理论值基本一致。但频率不足以抑制扭结模式。FRC等离子体通常被认为是一个不含环面场的细长致密环面。但放置在放电管表面的磁探头观察到一个方位波动磁场。信号的傅里叶分析表明，在整个放电过程中，n=1模态保持在一个较小的水平，而n=2模态随着旋转失稳的开始而增加。电流分布在n=1模式下为偶极轴向电流，在n=2模式下为四极轴向电流，两者均与FRC等离子体的轴向中间面对称。从离心力分离电荷的作用和电荷末端缩短的作用两方面解释了四重电流产生的机理。偶极电流似乎是由于等离子体在限定场中的运动而产生的。

The application of an axial current was proposed to form a field reversed configuration (FRC) plasma with a toroidal magnetic field. Effects of the axial current and threshold values of a successful FRC formation and confinement were investigated by NUCTE-3. Various frequencies (<=4.7x10^5rad/s) and amplitudes(<=6OkA) of axial currents were examined. In the formation phase, two effects were clarified ;(1) heating of the embedded plasma in the bias field (2) amplification of bias flux. In the confinement phase, the effect of stabilization of rotational instability were clarified. Though the kink instability was excited by a large axial current in both phases, it was confirmed that the instability can be avoided by using alternating current. Threshold value of the formation phase seemed to have relation with the poloidal flux limitation of a FRC formation and disturbances of preheating plasma and bias field. The stabilizing current value is almost the same as the theoretical value. But the frequency was not so high to suppress the kink mode.A FRC plasma is usually considered as an elongated compact toroid that contains no toroidal field. But an azumuthal fluctuating magnetic field was observed by magnetic probes located on the surface of the discharge tube. The Fourier analysis of the signals showed that the n=1 mode was kept at a small level throughout the discharge but the n=2 mode grew with onset of the rotational in- stability. Current distributions should be a dipole axial current for n=1 mode and a quadrupole axial current for n=2 mode, both of which are symmetrical to the axial mideplane of FRC plasma. The mechanism of the quadruple current generation was explained from the both effects of charge separation by centrifugal force and end shortening of the charge. The dipole current seemed to generate due to a plasma motion in the confining field.