Complex sheath formation around a spherical electrode in electronegative plasmas: a comparison between a fluid model and a particle simulation
Complex sheath formation around a spherical electrode in electronegative plasmas: a comparison between a fluid model and a particle simulation
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电负性等离子体中球形电极周围复杂鞘层的形成：流体模型与粒子模拟之间的比较
DOI：
10.1088/0022-3727/34/7/310
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发表时间：
2001
期刊：
影响因子：
--
通讯作者：
A. Kono
中科院分区：
文献类型：
--
作者：
A. Kono
使用流体模型以及细胞内粒子蒙特卡罗 (PIC-MC) 模拟对浸没在低压负电等离子体中的负偏压球形电极周围的等离子体壁边界结构进行了数值研究。等离子体参数的范围，例如负离子/电子密度比和电子/离子温度比，其中边界区域同时涉及正空间电荷和负空间电荷，是使用具有暖正离子以及具有和不具有正离子碰撞性的流体模型导出的。与平面放电的最新结果相反（Franklin R N 和 Snell J 2000 J. Phys. D：Appl. Phys. 33 1990），在放宽冷正离子假设的情况下，流体模型确实预测了具有非单调势的复杂鞘结构，即使对于与电子温度一样高的正离子温度（如果负离子温度足够低）。针对流体模型预测潜在振荡的情况，对流体模型和 PIC-MC 仿真进行了比较。在无碰撞极限下，PIC-MC 结果与流体模型结果几乎相同。然而，由于包含弱碰撞性，两种方法的结果存在巨大差异。虽然流体模型预测基本保持不变，但 PIC-MC 模拟显示出暂时振荡的非单调势，该振荡显然周期性地释放势阱中捕获的离子。这表明当流体模型预测空间势振荡时，会在真实物理势中引起不稳定。
The structure of the plasma-wall boundary around a negatively biased spherical electrode immersed in low-pressured electronegative plasma was studied numerically using a fluid model as well as a particle-in-cell Monte Carlo (PIC-MC) simulation. The range of plasma parameters, such as negative-ion/electron density ratio and electron/ion temperature ratios, in which the boundary region involves both positive and negative space charges, is derived using the fluid model with warm positive ions and with and without positive-ion collisionality. Contrary to the recent results for planar discharge (Franklin R N and Snell J 2000 J. Phys. D: Appl. Phys. 33 1990), with the cold-positive-ion assumption relaxed, the fluid model does predict a complex sheath structure with non-monotonic potential, even for positive-ion temperatures as high as the electron temperature if the negative ion temperature is sufficiently low. A comparison between the fluid model and PIC-MC simulation was made for a case where the fluid model predicts potential oscillations. In the collisionless limit, the PIC-MC results were almost identical with the fluid-model results. However, with weak collisionality included, the results from the two approaches differed drastically. While the fluid-model prediction remained essentially unchanged, the PIC-MC simulation showed a temporally oscillating non-monotonic potential, the oscillation apparently periodically releasing the ions trapped in the potential well. This indicates that when the fluid model predicts spatial potential oscillation, instability can be induced in the real physical potential.