杂质超声分子束注入过程中的输运物理研究

Impurity is one of the key issues in tokamak plasma research, as it is closely related to plasma confinement. Studying impurity transport and finding methods to control it will be very crucial for the construction and operation of future device ITER. At present, a newly developed fueling method named supersonic molecular beam injection (SMBI) has been widely applied to study impurity transport. By far, just a few theoretical studies have been done to research the transport of impurities introduced by SMBI, and even fewer 3D simulations works have been carried out for this study. This project aims to create a new self-consistent 3D transport model, including interactions between impurities and plasma, ionizations and radiations, to study the transport of impurities injected by SMBI. With the large collision database of ADAS, this model will be used to study collision reaction rates of different impurities. Then, based on this model and the existing transport module ‘trans-neut’ in BOUT++ boundary plasma turbulence code, a new module will be developed to study impurity transport in real tokamak geometry in entire space-time. With this module, the project will study the effects of different impurities on plasma profiles and transport coefficients in both L-mode and H-mode, through changing the condition of impurity injection (i.e. flux and position). At last, this project will study the properties of impurity transport, through comparing experiments of HL-2A tokamak and numerical works. The achievements of this project will provide important theoretical and experimental bases for many crucial studies, such as the edge impurity transport and the transport of high Z impurity in core.

杂质是影响托克马克等离子体约束性能的关键因素，研究杂质输运对将来ITER建设和运行有着重要的意义。目前，实验上运用了一种新型的超声分子束注入（SMBI）杂质的方法来研究杂质输运。可是关于SMBI注入杂质的输运理论研究非常少，进行三维数值模拟的研究更是匮乏。本项目拟建立一个SMBI注入杂质的自洽输运模型，包含杂质与等离子体自洽的相互作用、辐射等效应，且与ADAS数据库结合，计算各种杂质与等离子体碰撞反应率。接着，基于模拟程序BOUT++的输运模块‘trans-neut’，开发支持3D模拟研究SMBI注入杂质相关输运问题的新模块。项目将用该模块模拟低模与高模条件下杂质注入后的输运过程，并通过改变注入通量、位置等条件研究杂质对于等离子体剖面的影响。结合HL-2A开展的实验，综合对比不同杂质在超声分子束注入过程中的输运特性。研究成果将对研究杂质输运机制、偏虑器脱靶等关键问题提供重要理论和实验依据。

根据本项目研究目标升级了BOUT++程序中的SD1D模块与Atomic++模块，建立了包括主等离子体、中性粒子与杂质（如碳杂质和氖杂质）输运过程的模型。基于此模型，我们利用ADAS、Amjuel、Hydhel以及Yacora等数据库研究了两种主要的触发脱靶的方式：等离子体密度激增触发脱靶与杂质注入触发脱靶。发现（a）由器壁与等离子体碰撞反应产生的碳杂质能促进偏滤器靶板的脱靶过程；（b）偏滤器中再循环过程产生更高比例原子，能促进偏滤器的脱靶过程；（c）脱靶后偏滤器中H_alpha光子辐射强度的激增主要是由于分子反应导致的（如dissociative recombination， dissociative ionisation以及mutual neutralisation）；（d）在偏滤器中，氖杂质离子的在平行方向上的输运过程主要是由电子效应决定的（平行电场与电子热作用力electron thermal force）。为了进一步理解托克马克等离子体不稳定性与湍流导致的高能粒子溢出的机制以及对于器壁和靶板的影响，我们使用BOUT++的elm-pb了Kink-ballooning模与peeling-ballooning模对ELMs的影响，并且使用OMFIT 平台的集成模拟研究了NBI加热H模下的ETG与ITG不稳定性。发现（a）Kink-ballooning模在peeling-stable区域也能驱动边界莫不稳定性ELMs；（b）NBI功率沉积能抑制ETG不稳定性，将输运水平降至新经典水平，从而改善H模约束。