Research on modeling of peripheral plasma in a field-reversed configuration

1)研究了等离子体离子绕场反转结构分离矩阵旋转的运动。数值研究表明，当粒子通过场零点附近时，粒子的作用积分会发生突变。这种现象可以理解为俯仰角的无碰撞随机散射。对于具有正正则角动量Pe的粒子，散射前后作用积分的相关系数在某些情况下是随机的。在本研究中，分离矩阵内的磁通量函数定义为正。对于负PQ的粒子，随着作用积分的增加，它的运动趋向绝热。如果粒子的负PQ接近于零，则观察到随机运动。2)采用一维分析方法，研究了磁场对导流板的扩展作用下稳定鞘层的形成。等离子体鞘层边界对离子流速的要求比均匀磁场对离子流速的要求更严格，应大于离子声速。然而，两种情况之间的差异是德拜长度与等离子体半径的一个数量级，这个数量级可以忽略不计。考虑等离子体源的影响，得到了准中性等离子体内部离子流动速度的要求。在准中性等离子体中，如果没有等离子体源，则注入点的离子流速度应远大于离子声速。准中性等离子体内部的离子源，如电子冲击电离，大大减轻了这一要求。

1) The motion of a plasma ion gyrating around separatrix of a field-reversed configuration (FRC) is studied. Numerical studies showed that the action integral of a particle changes abruptly when a particle passes through the vicinity of a field null Xpoint. This phenomena is understood as collisionless stochastic scattering of the pitch angle. In the case of a particle with positive canonical angular momentum Pe, the resultant correlation coefficients of the action integral between before and after the scattering appear to be stochastic in some cases. In this studies the magnetic flux function inside the separatrix is defined positive. As the action integral increases foe a particle with negative PQ, its motion tends to be adiabatic. If the negative PQ of a particle approaches zero, a stochastic motion is observed. 2) The stable sheath formation in an expanding magnetic field to a divertor plate was studied by a one dimensional analysis. The requirement for flow velocity of ions at a plasma-sheath boundary is more restricted than that of the uniform magnetic field, which should be greater than the ion sound speed. The difference, however, between both cases is an order of the Debye length to plasma radius, which is negligibly small. The requirement for ion flow velocity inside a quasi-neutral plasma was obtained by taking into account the effects of the plasma source. Without plasma source in the quasi-neutral plasma, the ion flow velocity at an injection point should be much greater than the ion sound speed. The ion source inside the quasi-neutral plasma, such as electron impact ionization, considerably mitigates this requirement.