In negative ion sources, a cusped magnetic field is generated by magnets placed around each aperture of the extraction grid in order to limit the co-extracted electron current. In spite of this suppression magnetic field, the co-extracted electron current is large, on the same order as the negative ion current extracted from the plasma. In this paper, we study the mechanisms of electron extraction from the plasma through a cusped aperture in a simplified situation, in the absence of negative ions, with the help of a three-dimensional Particle-In-Cell Monte Carlo Collisions model. The calculation results show that the electron current extracted from the plasma is small for an infinite slit aperture with a suppressed (cusped) magnetic field and significantly increases in the case of finite slit or circular grid apertures. We find that the E × B electron drift plays an important role in the extraction of electrons through a finite slit grid aperture and that current driven micro instabilities are present in the aperture region. This work is relevant to negative ion sources and micro-ECR neutralizers designed for space propulsion.

中文翻译：

---

E × B 电子漂移电流穿过离子源孔径，被会切磁场轮廓包围

在负离子源中，通过放置在引出栅每个孔周围的磁铁产生会切磁场，以限制共同引出的电子电流。尽管有这种抑制磁场，但共提取的电子电流很大，与从等离子体中提取的负离子电流处于同一数量级。在本文中，我们借助三维细胞内粒子蒙特卡罗碰撞模型，在没有负离子的情况下，研究了在简化情况下通过尖孔从等离子体中提取电子的机制。计算结果表明，从等离子体中提取的电子电流对于具有抑制（尖峰）磁场的无限狭缝孔径很小，而在有限狭缝或圆形网格孔径的情况下显着增加。我们发现 E × B 电子漂移在通过有限狭缝栅格孔径提取电子方面起着重要作用，并且孔径区域存在电流驱动的微不稳定性。这项工作与为空间推进而设计的负离子源和微型 ECR 中和器有关。