The recycling of tritium from plasma facing wall is an important neutral fuel source (in atomic and molecular form) for plasma confinement and particle control. In this study, the recycling process at tungsten wall based on current CFETR design was modeled. Monte Carlo code SRIM was used to model the implantation of energetic tritium ions into pure tungsten and to get back-scattering fraction of ions and the distribution of implanted tritium ions. The diffusion process of atoms in materials, with recombination at surface as boundary condition, was simulated using numerical approach for both stead and transient state. The total recycling ratio was contributed by fast process (implantation and back scattering) and slow process (diffusion and recombination) and its value nearly equals to 1 for stead state. Temporal dependence of total recycling ratio mainly depended on the slow process and was limited by diffusion coefficient in the bulk near surface and existence of traps in material. For tungsten material with good surface condition, the time of 90% recycling was characterized as 1 ms and affected by temperature, recombination coefficient and concentration of traps while the thickness of material had less affection. Isotope effect that recycling ratio of tritium was larger than that of deuterium at the same situation was also found in the simulation and this effect may affect particle balance and fueling in D-T plasma operation. A collection of theoretical models to estimate the recycling ratio and its time dependence were also summarized and validated by the simulation results.

中文翻译：

---

现有CFETR设计中钨壁氚回收率的数值计算

从面向等离子体的壁中回收氚是用于等离子体约束和粒子控制的重要中性燃料源（以原子和分子形式）。在本研究中，对基于当前 CFETR 设计的钨壁回收过程进行了建模。Monte Carlo 代码 SRIM 用于模拟高能氚离子注入纯钨并获得离子的背向散射分数和注入的氚离子分布。原子在材料中的扩散过程，以表面复合为边界条件，采用稳态和瞬态的数值方法进行模拟。总回收率由快速过程（注入和背向散射）和缓慢过程（扩散和复合）贡献，其值几乎等于 1 稳态。总回收率的时间依赖性主要取决于缓慢过程，并受到近表面体中扩散系数和材料中存在陷阱的限制。对于表面状态良好的钨材料，其90%回收时间为1 ms，受温度、复合系数和陷阱浓度的影响，材料厚度的影响较小。模拟中还发现了在相同情况下氚的回收率大于氘的同位素效应，这种效应可能影响DT等离子体操作中的粒子平衡和燃料。模拟结果还总结并验证了一组用于估计回收率及其时间依赖性的理论模型。