Fully kinetic particle-in-cell simulations are carried out to study ion acceleration in a geometrically expanding plasma beam. The ion acceleration is demonstrated to be essentially self-similar. An analytical model is developed for ion acceleration evaluation. The plasma plume is found to be fully expanded after about 20 times of the beam radius (R ₀) downstream of the beam exit, where the ion velocity reaches the maximum. The maximum ion velocity increase is about twice of the initial ion acoustic speed. Hence, to minimize the facility effects on plasma plume experiments in a vacuum chamber, the chamber needs to provide a plume expansion region of at least 20R ₀ along the beam direction so the expansion process is not terminated prematurely.

进行完全动力学的细胞内粒子模拟以研究几何扩展等离子束中的离子加速。离子加速被证明基本上是自相似的。开发了用于离子加速评估的分析模型。发现等离子体羽流在射束出口下游约 20 倍射束半径 ( R ₀ )后完全膨胀，此时离子速度达到最大值。最大离子速度增加大约是初始离子声速的两倍。因此，为了尽量减少对真空室中等离子体羽流实验的设施影响，该室需要沿束流方向提供至少 20 R ₀的羽流扩展区域，以便扩展过程不会过早终止。