基于NEPTUNE3D开展的脉冲功率装置汇流区三维PIC数值模拟

大型脉冲功率装置真空汇流区的电子输运过程对于电流汇聚有重要的影响，在高性能计算集群的帮助下，使用NEPTUNE3D软件开展三维全电磁PIC模拟进行了研究，模拟区域（34 cm×34 cm×18 cm）包括双层柱-孔盘旋（DPHC）结构和部分内、外磁绝缘传输线等关键位置。计算结果清晰地展示了零磁位区分布和电子输运轨迹，电子主要由外磁绝缘传输线阴极表面发射，在洛伦兹力作用下向中心漂移并损失在零磁位区处；对电子能量沉积的统计结果表明，受电子流轰击最严重的位置在DPHC结构下层阳极柱表面，来自大型脉冲功率装置的实验结果证实了上述结论。根据计算结果，最大电流损失率（437 kA，27%）发生在电流传输的早期时刻（～15 ns），而电流峰值时刻损失率则仅有0.48%，此时磁绝缘已完全生效，表明DPHC结构在峰值电流的汇聚与传输上有很高的效率。

3D particle-in-cell simulations of current convolute structure on pulsed power facility using NEPTUNE3D

As electron transportation in vacuum convolute structure plays a quite important role during current converging process on pulsed power facility, fully three-dimensional (3D) particle-in-cell (PIC) simulations are performed using NEPTUNE3D code to explore this process. Simulated region (34 cm×34 cm×18 cm) including the double post-hole convolute (DPHC) structure is modeled and calculated with the help of high-performance computing clusters. The calculated results including the distributions of magnetic field nulls, trajectory of electron transportation, electrons lost on surfaces of anode posts, and time-integrated electron energy deposition damaging around the magnetic null areas between posts and holes, agree with the experimental ones from the large-scale pulsed power facility. According to the calculations, maximum current loss (437 kA, 27%) happens at early time (about 15 ns), while the loss drops dramatically to only 0.48% (34 kA) when current peaks at 53 ns (7.12 MA), at this time the magnetic insulations of transforming lines have been fully established, which also proves that the DPHC structure has especially high efficiency on high-density current converging.