A magnetic nozzle, which is a convergent-divergent magnetic field to control a plasma flow, has been investigated for application to plasma propulsion systems in spaceships. In the magnetic nozzle, plasma thermal energy is converted to one-directional kinetic energy by Lorentz force to generate thrust. Although magnetic field structure and strength are optimized for improvement of the thrust performance, it is essential to understand physical processes of plasma ejection from the nozzle, because the plasma may flow back along lines of magnetic field if the directed plasma continues being strongly magnetized. It is assumed, for one of the scenarios to explain a plasma detachment, that a plasma detaches from magnetic field when a cyclotron radius exceeds a scale length of magnetic field in size. Hence, we investigate a plasma detachment condition by analyzing parameters of the plasma for unmagnetization. We assumed individual particle motion of a fully ionized plasma in the magnetic nozzle and conducted a full particle-in-cell simulation in a two-dimensional coordinate system. We calculated a ratio of cyclotron radius to a scale length of the magnetic field. The ratio increased in a downstream due to variation of magnetic field induced from a diamagnetic cavity, suggesting unmagnetization.

已经研究了用于控制等离子流的会聚-发散磁场的磁性喷嘴，该磁性喷嘴可应用于飞船中的等离子体推进系统。在磁性喷嘴中，等离子体的热能通过洛伦兹力转换为单向动能以产生推力。尽管为改善推力性能而优化了磁场结构和强度，但必须了解从喷嘴喷射等离子体的物理过程，因为如果定向等离子体继续被强磁化，等离子体可能会沿着磁场线回流。对于解释等离子体分离的一种情况，假定当回旋加速器半径超过磁场的标度长度时，等离子体从磁场分离。因此，我们通过分析等离子体的未磁化参数来研究等离子体的脱离条件。我们假设了磁喷嘴中完全电离的等离子体的单个粒子运动，并在二维坐标系中进行了完整的单元内粒子模拟。我们计算了回旋加速器半径与磁场标度长度的比率。由于从反磁性腔中感应出的磁场的变化，该比率在下游增加，表明未磁化。