Study of ion separation mechanism in the multi-component vacuum arc discharge

Abstract. The separation phenomenon of light and heavy ions was widely observed experimentally in the vacuum arc discharge with multi-component composite cathode. In this work, a two-dimensional axisymmetric multi-fluid model is used to study the separation mechanism in the multi-component composite cathode vacuum arc. The multi-component vacuum arcs are simulated as a whole which includes separate cathode spot jets, the mixing region, and common arc column. The results show that the plasma jets originated from the separate cathode spot mix together to form a common arc column after a certain distance from the cathode. Due to the rapid increase of ion temperature dozens of times in mixing region of cathode spot jet, the effect of pressure gradient becomes far greater than that of the collisions between light and heavy ions. This leads to a shift in the predominant ion motion mechanism from ion–ion collision (single cathode spot jet region) to pressure expansion (the mixing region). Finally, the light ions gain higher velocities under pressure expansion. In addition, the effect of thermal conductivity and viscosity leads to the wider high temperature regions for light ions, thus making a wider distribution of corresponding ion flux. The numerical results are qualitatively consistent with the experimental results. This paper provides an insight into ion separation mechanism in the multi-component vacuum arc.

摘要。在多组分复合阴极的真空电弧放电实验中，广泛观察到轻重离子的分离现象。在这项工作中，使用二维轴对称多流体模型来研究多组分复合阴极真空电弧中的分离机制。对多组分真空电弧进行整体模拟，包括独立的阴极斑点射流、混合区域和公共弧柱。结果表明，源自独立阴极斑点的等离子体射流在距阴极一定距离后混合在一起形成公共弧柱。由于阴极斑点射流混合区域中离子温度迅速升高数十倍，压力梯度的影响变得远大于轻重离子之间的碰撞影响。这导致主要的离子运动机制从离子 - 离子碰撞（单个阴极斑点射流区域）转变为压力膨胀（混合区域）。最后，轻离子在压力膨胀下获得更高的速度。此外，热导率和粘度的影响导致轻离子的高温区域更宽，从而使相应的离子通量分布更宽。数值结果在定性上与实验结果一致。本文深入了解了多组分真空电弧中的离子分离机制。