直线装置靶板脱靶鞘层形成研究

Tokamak diverter detachment is a crucial aspect in reducing heat load to the target plate. Understanding its associated sheath structure is vital to improving controllability of diverter detachment through providing a basis to accurately predict and control plasma loss in such regime of operation, and might be related to other confinement behavior like the high density region. Linear devices are excellent platforms for studying sheath formation in detached plasmas as it generates a steady-state detached plasma in simple geometrical configuration. This facilitates accurate and highly spatially resolved plasma diagnosis compared to tokamak diverter plasmas where spatially resolved diagnosis along its sheath structure is almost impossible. Linear devices also enjoy the advantage of being relatively low cost with a more controllable operating schedule compared to tokamak devices, which means more experiments can be performed in a shorter frame of time..In this document a comprehensive study of detachment sheath structure is proposed utilizing the HPPX linear device. Plasma detachment can be achieved in this device at various electron temperature, electron density and plasma-neutral collisionality. Sheath/presheath temperature distribution, density distribution and potential structure in the detached plasma and its associated ion velocity distribution functions will be directed measured through axially movable Langmuir probes, emissive probes and laser induced fluorescence. The study is expected to result in an improved experimental and theoretical understanding of sheath formation in detached plasma, which become a basis of future tokamak diverter design and operation.

实现脱靶是聚变堆降低靶板粒子及热负载的重要的手段之一，了解脱靶状态下的鞘层结构是准确预测及控制等离子体损失方式的重要前提，而且可能与脱靶状态的约束性现象如高密度区有所关联。为实现对脱靶更可靠的控制，需要针对脱靶状态下的鞘层结构开展全面的实验研究。直线装置具有结构简单、诊断可近性好、运转周期短等优点，在相关研究上具有独特的优势。本项目拟在HPPX直线装置中改变等离子体温度及靶板充气速率控制脱靶状态，并利用发射探针、激光诱导荧光等测量方法，实现电势结构以及离子速度分布的直接诊断。进而，评估脱靶状态下等离子体鞘层结构及相关离子速度分布形成的潜在机理。本项目的开展将显著提升我们对脱靶的形成过程与离子输运机理的认知水平，促进对脱靶状态的有效控制，并为未来聚变堆实现稳态脱靶运行的设计目标提供重要的实验基础和理论依据。

本项目的原定目标为依托HPPX直线装置的大功率螺旋波和ECR放电，深入探究脱靶鞘层形成条件的深入研究及脱靶鞘层是否存在相应预鞘及玻姆判据的实验验证。但是由于原依托平台的解体、疫情打击、实验室拆迁等事件影响，实质深入探索这两个目标研究工作的硬件建设受到较大影响。即便如此，项目组仍然围绕实现本项目研究目标，积极开展项目所需的诊断技术及物理研究，并开展了新的脱靶鞘层形成相关理论的实验论证，在这些方面的工作上获得了比较丰富的成果，包括朗缪尔探针自动化分析建设、快扫朗缪尔探针的技术及物理研究、电子鞘层形成及有限腔体面积或过大探针面积对朗缪尔探针数据准确性的影响、激光诱导荧光诊断的激光调制频率极限探索等。此外，我们针对新近形成的反鞘理论进行了实验探索，为另一种潜在脱靶机制的理论率先提供了实验验证。在本项目的大力支持下，项目组已经具备了后续深入进行相关研究的物质及技术基础。此外，本项目成果主要为朗缪尔探针及激光诱导荧光相关的诊断物理研究，而这些诊断在国内电推进及其他低温等离子体物理研究领域中具有广泛的需求和应用，尤其激光诱导荧光在电推进领域正处于需求大、发展高速的阶段，因此本项目成果对这些研究领域也将所助益。在未来的工作中，项目组将进一步加紧开展脱靶鞘层形成的实验研究，从而深化对于碰撞性鞘层及脱靶状态相关物理的认识水平。