标题： 回旋动力学与流体刮除层模拟的直接比较 显示英文标题

标题： Direct Comparison of Gyrokinetic and Fluid Scrape-Off Layer Simulations

摘要： 通常，流体模拟被用于托卡马克偏滤器设计。然而，流体模型仅在边缘等离子体（SOL）高度碰撞的情况下有效，这一假设在许多当前实验中成立，但在燃烧等离子体和聚变试点工厂的高功率场景下则值得怀疑。本文报告了针对类似于能源生产球形托卡马克（STEP）聚变试点工厂参数和几何形状的刮擦层（SOL）的流体与动能模拟之间的比较。SOLPS-ITER（流体）和Gkeyll（ gyrokinetic）代码以二维轴对称模式运行，该模式用经验扩散率代替了湍流。在动能模拟中，我们观察到上游SOL中的离子经历显著的镜像捕获。这大大提高了上游温度，并对杂质动力学具有重要意义。我们展示了在SOLPS流体方程形式中排除的镜像力增强了SOL中沿磁场线的静电势降。我们还显示了在常用流体代码中假设的主要离子和杂质温度相等是无效的。这些效应的结合导致动能模拟中杂质向偏滤器区域的优越限制，与我们早期的预测一致。这种影响可能是戏剧性的，将等离子体中部的杂质密度降低几个数量级。这些结果表明，在反应堆类似的工作条件下，下游杂质密度可容忍的程度可能高于流体模拟所预测的，允许更高的辐射功率，同时避免不可接受的核心污染。我们的结果强调了动能模拟对于聚变试点工厂偏滤器设计和优化的重要性。 显示英文摘要

摘要： Typically, fluid simulations are used for tokamak divertor design. However, fluid models are only valid if the SOL is highly collisional, an assumption that is valid in many present day experiments but is questionable in the high-power scenarios envisioned for burning plasmas and fusion pilot plants. This paper reports on comparisons between fluid and kinetic simulations of the scrape off layer (SOL) for parameters and geometry representative of the Spherical Tokamak for Energy Production (STEP) fusion pilot plant. The SOLPS-ITER (fluid) and Gkeyll (gyrokinetic) codes are operated in a two-dimensional (2D) axisymmetric mode, which replaces turbulence with ad-hoc diffusivities. In kinetic simulations, we observe that the ions in the upstream SOL experience significant mirror trapping. This substantially increases the upstream temperature and has important implications for impurity dynamics. We show that the mirror force, which is excluded in SOLPS's form of fluid equations, enhances the electrostatic potential drop along the field line in the SOL. We also show that the assumption of equal main ion and impurity temperatures, which is made in commonly used fluid codes, is invalid. The combination of these effects results in superior confinement of impurities to the divertor region in kinetic simulations, consistent with our earlier predictions. This effect can be dramatic, reducing the midplane impurity density by orders of magnitude. These results indicate that in reactor-like regimes the tolerable downstream impurity densities may be higher than would be predicted by fluid simulations, allowing for higher radiated power while avoiding unacceptable core contamination. Our results highlight the importance of kinetic simulations for divertor design and optimization for fusion pilot plants.