We present the results of a direct simulation of the expansion of a two-component ultracold plasma for various numbers of particles, densities, and electron temperatures. A description of the expansion process common to all plasma parameters is given. After the escape of fast electrons from the plasma cloud, the excess positive charge is localized at the outer boundary, in a narrow layer. This layer has a characteristic front shape with a sharp drop in the charge concentration. The charged layer retains the remaining electrons during the entire expansion process. As the plasma expands, the speed of movement of the charged layer becomes constant and significantly exceeds the sonic speed of ions. In addition, the dependence of the radial velocity of ions on the radius acquires a self-similar character long before the final stage of expansion. Based on the calculation results, equations and self-similar solutions are obtained. General dependencies on plasma parameters are determined, which are compared with experimental data.

中文翻译：

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超冷等离子体膨胀过程中的离子波形成

我们展示了对不同数量的粒子、密度和电子温度的双组分超冷等离子体膨胀的直接模拟结果。给出了对所有等离子体参数通用的膨胀过程的描述。等离子云中的快速电子逸出后，多余的正电荷位于外边界的狭窄层中。该层具有特征性的前沿形状，电荷浓度急剧下降。在整个膨胀过程中，带电层保留了剩余的电子。随着等离子体的膨胀，带电层的运动速度变得恒定并且明显超过离子的声速。此外，离子径向速度对半径的依赖性在膨胀的最后阶段很久之前就获得了自相似特性。根据计算结果，得到方程和自相似解。确定对等离子体参数的一般依赖性，并将其与实验数据进行比较。