EAST高约束模辐射偏滤器运行下的边界杂质输运行为研究

EAST and future ITER will operate in the long-pulse, high-confinement mode, and the divertor target will therefore be subject to excessive particle flow and heat flux from the high temperature core plasma. The radiative divertor is used to reduce the sputtering and thermal deposition power of the target surface by radiation and charge exchange in the boundary plasma region by appropriately introducing impurity gases. However, the radiative divertor operation will inevitably bring about the problem of impurity transport, which affects the confinement performance of the core plasma. Based on the mega science project EAST and by means of the combination of radiative divertor experiments and SOLPS and DIVIMP simulations, The effect of different types of edge localized modes (ELMs) on the transport mechanism of impurities such as argon, neon and tungsten will be investigated during the operation of EAST high-confinement mode and radiative divertor. On the other hand, the sputtering effect of impurities and background plasma on tungsten target surface and the effect of impurity transport on plasma confinement performance during different ELMs bursts will be studied. In addition, physics methods will be explored for inhibiting the transport of impurities to the core plasma and reducing the sputtering of impurities on the tungsten target surface to ensure the EAST safely under high-power, long-pulse operation. These works are expected to provide valuable reference for future ITER and CFETR operation.

EAST以及未来的ITER都将运行在长脉冲高约束模式，偏滤器靶板将会因此承受来自芯部高温等离子体的过量的粒子流和热流。辐射偏滤器通过适当引入杂质气体，在边界等离子体区域通过辐射和电荷交换降低靶板表面的溅射和热沉积功率。但辐射偏滤器运行不可避免的带来了杂质输运问题，影响到芯部等离子体的约束性能。本项目将依托EAST大科学工程，结合辐射偏滤器实验和SOLPS、DIVIMP等程序模拟，研究EAST高约束模辐射偏滤器运行时不同类型的边界局域模（ELMs）对氩、氖、钨等杂质输运机制的影响，分析在不同ELMs爆发期间，杂质与背景等离子体对钨靶板材料的溅射效应以及杂质输运对等离子体约束性能的影响，探讨抑制杂质向芯部输运并减少杂质对钨靶板材料表面溅射的物理方法，保障EAST装置在高功率长脉冲下稳定运行，为将来的ITER和CFETR的运行提供参考。

EAST以及未来的ITER都将运行在长脉冲高约束模式，偏滤器靶板将会因此承受来自芯部高 温等离子体的过量的粒子流和热流。辐射偏滤器通过适当引入杂质气体，在边界等离子体区域 通过辐射和电荷交换降低靶板表面的溅射和热沉积功率。但辐射偏滤器运行不可避免的带来了杂质输运问题，影响到芯部等离子体的约束性能。在本项目的支持下，完成了EAST辐射偏滤器硬件系统的升级改造。在此基础上开展了Ar和Ne不同杂质注入下的高约束模辐射偏滤器物理实验，进行了不同类型ELMs和Ar、Ne、W等杂质相互作用的实验和模拟研究，同时开展了“上游充D2+下游充Ar”下的辐射偏滤器脱靶与芯部兼容性研究，并通过SOLPS-ITER对EAST辐射偏滤器条件下的等离子体脱靶物理过程进行了分析。通过以上研究实现了EAST高约束模放电时ELMs控制和辐射偏滤器脱靶的兼容，杂质气体注入缓解了大ELM，降低了靶板稳态和瞬态热负荷，从而使靶板得到了有效保护，同时芯部约束性能没有明显下降。通过理论分析发现Ne注入放电中ELM被抑制的主要原因可能是Zeff的大幅增加降低了台基自举电流，增强了台基碰撞，并随着杂质稀释降低了主离子密度的压力梯度，从而使PBMs稳定，大的ELM被抑制。在EAST上发展的“上游充D2+下游充Ar”的辐射偏滤器运行模式能够在实现靶板稳定脱靶的同时抑制W、Ar等高Z杂质进入芯部，维持较好的芯部约束。以上研究结果保障了EAST 装置在高功率长脉冲下稳定运行，为将来的ITER和CFETR的运行提供了参考。