束-等离子体系统中电子鞘特性的实验研究

Plasma electron sheaths exist widely in the vicinity of positively biased electrodes. Because of the extremely narrow spatial extent (usually about one order of magnitude smaller than that of ion sheaths near negatively biased electrodes), the diagnostics of the sheath profiles is difficult, and thus the experimental investigations on the electron sheaths thus far were rather few. Beam-plasma systems exist universally in space environments (e.g., in the surroundings of spacecrafts and geospace environment), laboratory plasmas, and low-temperature plasma technologies. The existence of particle beams will significantly affect the sheath structures. In such systems, however, only ion sheaths were studied by a few researchers, the electron sheaths have not been studied yet. The preliminary experiment in our group showed that a virtual cathode appeared inside the electron sheath when there was an incident beam, but the mechanism of the appearance and the characteristics of the virtual cathode structure are not clear. Aimed at these problems, the proposed project will experimentally investigate the characteristics of the electron sheaths in the beam-plasma-system in a double plasma device, and study the general properties of the sheath profiles and the influence of the beam on the virtual cathode. This study will deepen the understanding of the diversity and complexity of the sheath structures, and will have potential applications in the above mentioned areas.

等离子体中的电子鞘广泛存在于正偏压的电极附近，由于空间尺度很小(通常比负偏压电极附近的离子鞘小约一个数量级)，不容易诊断鞘层结构，至今有关电子鞘的实验研究极少。束-等离子体系统普遍存在于空间环境(如航天飞行器周围和近地空间)、实验室等离子体、以及低温等离子体工艺等领域，粒子束的存在对鞘层结构产生重要影响，但在该系统中只有离子鞘被少数实验室研究过，尚无有关电子鞘的研究。本课题组的预研实验表明有束入射时电子鞘中会出现虚阴极结构，但出现虚阴极的机制及其结构特性尚不清楚。针对这些问题，本项目拟在双等离子体装置中开展束-等离子体系统中电子鞘特性的实验研究，探究此系统中电子鞘结构的一般特性，以及束的存在对虚阴极结构的影响。该项研究对深入理解鞘层结构的多样性和复杂性具有重要学术意义，且在上述一些领域可能有潜在应用。

等离子体鞘层是等离子体物理中一个典型的基础研究课题，对此研究不仅有一定学术价值，而且在低温等离子体技术、聚变等离子体、航天等领域也有现实意义。本项目针对束等离子体系统这一特定情况下的鞘层结构进行实验研究，取得如下结果：.1.在DPD等离子体装置中，通过实验区和源区的电位控制，在实验区成功引入了低能量的电子束和离子束。.2.在离子束-等离子体中测量了精细的电子鞘结构，发现鞘层结构中电子鞘通过离子鞘连接到主等离子体区。.3.在引入电子束的情况下，测量了电子鞘的电势分布，发现鞘层的厚度与束能量有关。.4.测量了会切场中鞘层结构，并在离子束等离子体中栅网鞘层中研究了双迸发离子模。.鞘层结构的实验研究有助于对聚变等离子体中壁边界问题和低温等离子体中等离子体材料相互作用更深入的理解。