This paper presented the particle-in-cell simulations on the expansion process of the plasma with a density about 1014 cm-3 near the cathode surface. The plasma expanding with velocity about 1 cm/μs was observed. The expansion process was analyzed based on the observations of the particle distributions, the particle velocity and the axial electric field at different time. The influences of the plasma temperature and plasma formation rate on the plasma expansion process were discussed. It is shown that the appearance of ions strengthens the electric field on the cathode surface, leading to the increase of electron beam density. The electron field at the plasma front decreases with the increase of beam density, thus the movement of ions towards anode can be realized. The plasma expansion velocity increases while the plasma temperature grows up. However, the relationship of thermal velocity can not apply. Smaller plasma formation rate leads to lower plasma expansion.%模拟了强流电子束源阴极表面附近区域数密度约1014 cm-3的等离子体的膨胀过程,观察到等离子体膨胀速度约为1 cm/μs.通过观察不同时刻阴极附近电子和离子的相空间分布、数密度分布和轴向电场分布,分析了等离子体膨胀过程.结果表明:等离子体的产生使得阴极表面电场增强,进而增大阴极的电流发射密度,电流密度增加使得空间电荷效应增强,并使等离子体前沿处的电场减小,当等离子体前沿处的电场减小到零时等离子体向阳极膨胀.讨论了等离子体温度、离子质量、束流密度和离子产生率对等离子体膨胀速度的影响.结果表明:等离子体的膨胀速度随着等离子体温度升高而增大,随离子质量增大而减小,但膨胀速度不等于离子声速；等离子体产生率越小,等离子体膨胀速度越小.
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