Neutral particles in the plasma edge of fusion devices based on magnetic confinement are described by a transient kinetic equation incorporating ionization, recombination, and charge-exchange collisions. In charge-exchange dominated regimes, the neutral particle velocity distribution approaches the drifting Maxwellian defined by the mean velocity and temperature of the plasma. This enables model order reduction from the kinetic equation to approximate fluid models. We derive transient fluid models consistent with the kinetic equation by exploring a splitting based approach. We split the kinetic equation in sources and sinks on the one hand, and transport combined with charge-exchange on the other hand. Combining transport with charge-exchange collisions allows for deriving Hilbert expansion based fluid models. The retrieved fluid models depend on the assumed importance (scaling) of the different terms in the split equation describing transport and charge-exchange. We explore two scalings: the hydrodynamic scaling and the diffusive scaling. The performance of the fluid models with respect to a discrete velocity model and a Monte Carlo reference solver is assessed in numerical experiments. The code used to perform the numerical experiments is openly available.

翻译：基于磁约束的聚变装置等离子体边缘中性粒子由包含电离、复合及电荷交换碰撞的瞬态动力学方程描述。在电荷交换主导的区域内，中性粒子速度分布趋近于由等离子体平均速度与温度定义的漂移麦克斯韦分布。这实现了从动力学方程到近似流体模型的模型降阶。我们通过探索一种分裂方法，推导出与动力学方程一致的瞬态流体模型。我们将动力学方程分裂为源项与汇项，以及输运与电荷交换耦合项。将输运与电荷交换碰撞相结合，可推导出基于Hilbert展开的流体模型。所获得的流体模型取决于描述输运与电荷交换的分裂方程中各不同项假设的重要性（标度）。我们研究了两种标度：流体动力学标度与扩散标度。通过数值实验，评估了这些流体模型相对于离散速度模型和蒙特卡洛参考求解器的性能。用于开展数值实验的代码已公开提供。