用电子注入中和离子束第1部分：冷电子的积累
Neutralization of ion beam by electron injection, Part 1: Accumulation of cold electrons
摘要：
电子注入离子束电荷中和是一个复杂的动力学过程。最近的实验表明，在被等离子体中和之后，所产生的束的自电势可能远低于等离子体电子的温度[Physics of Plasmas 23，043113（2016）]，这表明动力学效应是重要的，并且可能影响离子束的中和。我们进行了一个数值研究的电荷中和过程的离子束利用二维静电粒子在细胞的代码。结果表明，电子注入电荷中和过程由两个阶段组成。在第一阶段，束的自电势高于注入电子的温度（Te/e）。因此，离子束的中和几乎不受Te的影响，并且所有注入的电子都被离子束捕获。在第二阶段，随着束流电势的下降（），热电子从离子束中逃逸，而冷电子则慢慢积累。因此，可以远低于Te/e。在模拟中发现，在冷电子的积累过程中，尺度为。此外，计算结果还表明，电子源的横向位置对离子束中和有很大的影响。电子源的微小位移会使注入电子的势能增大，从而导致束流电势的大幅度增加。
英文摘要：
Ion beam charge neutralization by electron injection is a complex kinetic process. Recent experiments show that resulting self-potential of the beam after neutralization by plasma could be much lower than the temperature of plasma electrons [Physics of Plasmas 23, 043113 (2016)], indicating that kinetic effects are important and may affect the neutralization of ion beam. We performed a numerical study of the charge neutralization process of an ion beam making use of a two-dimensional electrostatic particle-in-cell code. The results show that the process of charge neutralization by electron injection is comprised of two stages. During the first stage, the self-potential of the beam is higher than the temperature of injected electrons (Te/e). Therefore, the neutralization of the ion beam is almost unaffected by Te, and all injected electrons are captured by the ion beam. At the second stage, with the decline of the beam potential (), hot electrons escape from the ion beam, while cold electrons are slowly accumulated. As a result, can be much lower than Te/e. It is found in the simulations that during the accumulation of cold electrons, scales as . In addition, the results show that the transverse position of electron source has a great impact on ion beam neutralization. Slight shift of electron source leads to large increase of the beam potential because of increase in potential energy of injected electrons.
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