Electrons neutralizing the ion beam from a gridded ion source are typically provided by an external cathode. This cathode emits a continuous current that ensures quasi-neutrality of the plume, and current balance of the ion source. A new type of neutralization scheme has recently been identified in the context of radio-frequency (RF) biased ion sources, where instead of a continuous electron current, the plume is neutralized by electron pulses emitted from the same plasma source as the ion beam itself. In contrast to conventional gridded ion sources, experiments have shown that pulsed neutralization produces hot electrons with a strongly anisotropic energy distribution in the plume. By making use of a two-dimensional particle-in-cell (PIC) simulation, we analyze the pulsed neutralization and plasma expansion to understand the fundamental plume physics in these systems, and perform a direct comparison with the expansion observed in typical DC systems. Electron trapping in the near-field plume region is found to be critical for ensuring quasi-neutrality, and the plume potential is observed to be higher than the downstream acceleration grid potential to prevent excessive electron backstreaming into the plasma source. This potential difference results in the formation of high-energy electron beams that generate collective plume oscillations with frequencies above the applied RF frequency. A detailed parametric study is performed to investigate the influence of the pulse frequency, emission current, and capacitance between the source and outer surrounding boundaries. In particular, the pulse frequency and emission current have a significant effect on the resulting plume potential, and the effectiveness of the resulting ion beam neutralization.

中和来自网格离子源的离子束的电子通常由外部阴极提供。该阴极发出连续电流，确保羽流的准中性和离子源的电流平衡。最近在射频 (RF) 偏置离子源的背景下确定了一种新型的中和方案，其中，羽流被从与离子束本身相同的等离子体源发射的电子脉冲中和，而不是连续的电子流. 与传统的网格离子源相比，实验表明脉冲中和产生的热电子在羽流中具有强烈的各向异性能量分布。通过使用二维细胞内粒子 (PIC) 模拟，我们分析脉冲中和和等离子体膨胀以了解这些系统中的基本羽流物理，并与典型直流系统中观察到的膨胀进行直接比较。发现近场羽流区域中的电子俘获对于确保准中性至关重要，并且观察到羽流电位高于下游加速栅极电位，以防止过多的电子回流到等离子体源中。这种电位差导致高能电子束的形成，这些电子束产生频率高于应用射频频率的集体羽流振荡。执行详细的参数研究以研究脉冲频率、发射电流和源与外部周围边界之间的电容的影响。特别是，