托卡马克刮削层和偏滤器等离子体粒子模拟研究

Tokamak Scrape-Off Layer/Divertor (SOL/DIV) plasma is one of the most crucial subjects in the magnetic confined fusion research areas. It is related directly with the choice and lifetime of plasma-facing materials, and the steady-state operation of the fusion devices. High-confinement mode (H-mode) in company with edge localized modes (ELMs) is an extremely important operation regime for a steady-state operation machine, since it can maintain the capability of tokamak confinement through periodically expelling impurities and energy from core plasma. However, ELMs lead to a fast loss of energy and particles from the plasma edge, and these transient bursts of energy and particles into the SOL produce high peak heat loads on the divertor plates which bring a great threat to the target lifetime. Divertor detachment is the best solution to decrease the heat load to divertor plates. The aim of this project is to study the kinetic characteristics of the SOL/DIV plasma with the development of a parallelization code based on the self-consistent particle-in-cell (PIC) simulation model. The project contains:1.SOL/DIV plasma simulation during the occurrence of ELMs. In this work, the energy and particle fluxes to the divertor plates will be studied to establish a qualitative understanding of the influence of several key parameters (i.e. characteristic plasma ELM energy loss) under different types of ELMs, and the resulting erosion of tungsten divertor. The effect of collisionalty and radiative cooling during ELMs on the heating and particle fluxes to the divertor will also be clarified. 2. Simulation of the dynamic processes of plasma during divertor detachment. The PIC-DSMC (direct simulation Monte Carlo) model is applied to simulate the effects of different collision processes and neutralization-recycling of charged particles at the surface during the detachment. The influence of the amount and the type of the injected gas on the detachment will also be investigated.

托卡马克中刮削层和偏滤器（SOL/DIV）等离子体是核聚变研究领域的一个重要课题，直接关系到器壁材料的选择以及装置能否长久稳态运行。ELMs可以排除聚变反应产生的氦灰和能量，未来聚变装置必须采用伴有ELMs 的H模运行方式，但这会对偏滤器靶板的能流负载造成很大压力，实现偏滤器脱靶是降低能流负荷的最有效方法。针对SOL/DIV中等离子体动力学行为，本项目自主开发并行化SOL/DIV 粒子模拟程序，包括两方面研究内容：1. ELMs 时SOL/DIV 等离子体模拟。主要研究不同类型ELMs 时入射到偏滤器靶板的能流和粒子流以及器壁的侵蚀状况，同时对等离子体中的碰撞和辐射效应开展研究。2.偏滤器脱靶动力学模拟研究。采用PIC-DSMC 耦合的方法研究不同碰撞和壁表面带电粒子的中性化- - 再循环过程在脱靶中起到的作用，以及辐射偏滤器中喷入的气体量和气体种类对实现脱靶的影响。

核聚变能是彻底解决能源问题的最有效方案，而最有望实现聚变的装置极为托卡马克。偏滤器是托卡马克放电过程中控制杂质和燃料再循环以及排灰的有效部件，在高功率加热情况下偏滤器靶板的承热存在巨大的挑战，使用物理方法减小入射到靶板的能流和粒子流就变得极其重要。刮削层和偏滤器等离子体是当今磁约束核聚变研究领域的一个重要课题，直接关系到器壁材料的选择和寿命以及聚变装置能否长久稳态运行。针对托卡马克刮削层和偏滤器等离子体进行数值模拟研究。主要针对三点开展了研究：1. 不同等离子体条件下（包括ELMs）入射到偏滤器靶板的能流和粒子流，以及导致的钨偏滤器靶板的侵蚀。分别开展了一维和二维研究，研究区域包含偏滤器靶板以及靶板缝隙等离子体，同时考虑了不同杂质粒子对钨侵蚀的影响。2. 偏滤器脱靶模拟研究，主要研究脱靶的形成过程，不同原子分子反应对脱靶的影响，以及杂质（包括充入杂质气体）对实现脱靶的影响。研究中分析了氢离子同分子之间的碰撞、中性粒子之间的碰撞对脱靶的影响，同时分析了注入氩气和锂等杂质对实现脱靶的影响。通过本项目研究不同条件下入射到偏滤器靶板的能流、粒子流情况得到钨靶板的侵蚀，理解脱靶的实现过程，对托卡马克实验的优化改进提供参考依据和合理建议。3.研究了ELMy H-mode期间燃料在钨材料中的滞留行为。研究表明当发生ELMs时由于存在离子诱导缺陷，滞留量显著增加。同时开展了气泡在钨材料中的生长行为模拟，研究表明气泡的级联碰撞和气泡内部的高气压是导致气泡生长的主要原因。