非结构运动网格上的半隐式各向异性cosmic ray输运
Semi-implicit anisotropic cosmic ray transport on an unstructured moving mesh
摘要：
在星系的星际介质和星系团的团内气体中，构成宇宙射线的带电粒子几乎完全沿着（但不是穿过）磁场线运动。由此产生的宇宙射线以扩散或流动形式的各向异性传输不仅影响气体动力学，而且还会重新排列磁场本身。因此，磁场和宇宙射线的耦合动力学可以以关键的方式影响星系的形成和演化以及星系团的热演化。数值研究这些影响需要求解器的各向异性扩散是准确的，有效的，和强大的，要求已被证明难以满足在实践中。在这里，我们提出了一个非结构化的移动网格上的各向异性扩散求解器是保守的，不违反熵条件，允许半隐式的时间积分与个人的时间步长，只需要解决一个单一的线性方程组，每个时间步长。我们将我们的新方案应用于大量的测试问题，并表明它的工作以及或优于以前的实现。最后，我们证明了一个孤立的盘星系的形成，我们的本地时间步进方案再现了全球时间步进的计算成本的一小部分所获得的结果的数值模拟要求。
英文摘要：
In the interstellar medium of galaxies and the intracluster gas of galaxy clusters, the charged particles making up cosmic rays are moving almost exclusively along (but not across) magnetic field lines. The resulting anisotropic transport of cosmic rays in the form of diffusion or streaming not only affects the gas dynamics but also rearranges the magnetic fields themselves. The coupled dynamics of magnetic fields and cosmic rays can thus impact the formation and evolution of galaxies and the thermal evolution of galaxy clusters in critical ways. Numerically studying these effects requires solvers for anisotropic diffusion that are accurate, efficient, and robust, requirements that have proven difficult to satisfy in practice. Here, we present an anisotropic diffusion solver on an unstructured moving mesh that is conservative, does not violate the entropy condition, allows for semi-implicit time integration with individual timesteps, and only requires solving a single linear system of equations per timestep. We apply our new scheme to a large number of test problems and show that it works as well or better than previous implementations. Finally, we demonstrate for a numerically demanding simulation of the formation of an isolated disk galaxy that our local time-stepping scheme reproduces the results obtained with global time-stepping at a fraction of the computational cost.
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