EAST低杂波天线端口热斑形成及其对天线损伤机理的研究

Lower hybrid wave (LHW), the most efficient radio frequency (RF) power for current generation, will provide indispensable current to sustain the steady state, high performance and long pulse operation in tokamaks. However the fast electrons driven by the LHW along the magnetic field could produce local hot spots on the first wall and lead to severe erosion of the wall material. In EAST, hot spots produced by the fast electrons driven by the LHW have seriously restricted the injected power of LHW and made it difficult to achieve high performance and long pulse discharges. This project aims to elucidate the physical mechanism of the formation and evolution of the hot spot and its erosion to the guard limiters. To reveal the dependence of sputtering product of guard limiter caused by hot spot on the plasma parameters, the applicant plans to work as follows: upgrading the retarding field analyzer in engineering; analyzing the dependence of the current and heat flux carried by the fast electrons on the plasma density and LHW injecting power in experiment; developing a physical model to study how the current and heat flux carried by the fast electrons influence the sheath potential and wall temperature of the guard limiters respectively. The implementation of this project will shed light on how to solve the restriction of high performance and long pulse operation brought by the hot spots for EAST and future fusion reactor.

低杂波作为射频波中电流驱动效率最高的射频源，在未来聚变堆运行中将提供不可或缺的电流驱动份额以维持稳态高参数长脉冲运行。然而低杂波在刮削层中沿磁力线驱动快电子在壁上形成局域热斑对装置壁造成严重损害。在EAST超导托卡马克上低杂波在天线口驱动快电子产生的热斑刻蚀天线端口造成杂质大量溅射，严重制约着低杂波天线出波功率，并导致高参数长脉冲等离子体放电难以为继。本项目旨在从物理机制上阐明热斑形成和演化及其对天线保护限制器刻蚀的机理。通过在工程上升级减速场能量分析仪，在实验上分析快电子驱动电流和能流随等离子体密度和低杂波加热功率的演化关系，在理论上发展模型研究热斑处快电子驱动电流对靶板鞘层的影响以及快电子驱动能流对靶板温升的影响，揭示热斑造成的器壁物理溅射产额和化学溅射产额与等离子体参量的依赖关系。本项目的开展将为解决EAST和未来聚变堆上热斑限制高参数长脉冲放电提供重要的科学依据。

低杂波作为射频波中电流驱动效率最高的射频源，在未来聚变堆运行中将提供不可或缺的电流驱动份额以维持稳态高参数长脉冲运行。然而低杂波在刮削层中沿磁力线驱动快电子在壁上形成局域热斑对装置壁造成严重损害。在EAST超导托卡马克上低杂波在天线口驱动快电子产生的热斑刻蚀天线端口造成杂质大量溅射，严重制约着低杂波天线出波功率，并导致高参数长脉冲等离子体放电难以为继。本项目从物理机制上解释了热斑形成和演化及其对天线保护限制器刻蚀的物理机理。在项目基金的支持下，在工程上升级了减速场能量分析仪，在实验上研究了等离子体密度和低杂波加热功率与溅射碳杂质浓度的演化关系，在理论上发展了模型研究热斑处快电子驱动电流对靶板鞘层的影响，并结合刻蚀程序计算了碳杂质溅射产额在放电期间的时间演化以及与等离子体参数的依赖关系。揭示了热斑造成的器壁化学溅射产额随着等离子体放电密度（较高密度区）和天线口能流的增加而增加，这可能是引发碳杂质迸发的诱因。本项目的成果将为解决EAST和未来聚变堆上热斑限制高参数长脉冲放电提供重要的科学依据。