等离子体扩散流中金属平板上下游的鞘层结构

Upstream and downstream sheath structures near a metal plate in the flow of a diffusive plasma

利用发射探针诊断了处于扩散等离子体流场中平板两侧的鞘层电势分布并给出鞘层厚度及边界电场。结合Child-Langmuir(CL)定律并利用一维流体模型,分析对比了鞘厚及边界电场。结果显示,上下游的鞘层呈现不对称结构,下游比上游厚,边界电场下游比上游弱,并且下游的预鞘还呈现类似虚阳极的结构。上下游CL鞘的厚度满足线性比例关系,比例系数约为1.2,且实验值与理论值非常接近。上下游CL鞘的边界电场与模型Te/(eλD)比较接近,上游Bohm鞘边界电场的实验结果与过渡区模型e/(3D/5i2/5)T e较符合,但下游Bohm鞘的边界电场与现有模型有较大差异。

The potential distributions in the sheath and presheath in the upstream and downstream sides of a metal plate immersed in the flow of diffusive plasma were measured using a fine structured emissive probe, Combining the Child-Langmuir（CL） law and one-dimensional fluid model, the sheath thicknesses and edge electric fields were analyzed. It is shown that the sheath in the downstream side is thicker than that in the upstream side, while the measured edge electric field of the upstream sheath is stronger than that of the downstream sheath. Both experimental and numerical results show that the thicknesses of the CL sheath in the two sides of the plate satisfy a linear relation, with a fitting proportionality of 1.2 between the down- and upstream thickness. The electric field at the CL sheath edge in both up-and downstream sides is consistent with the value given by Te Te（eλD）, while the measured electric field at the Bohm sheath edge in the upstream side is close to Te/（eλd^[3/5]λ1^[2/5]＇）. However, the Bohm sheath edge electric field in the downstream side shows a significant deviation from available models.