耦合Landau封闭多流体动力学与粒子网格法
Coupling multi-fluid dynamics equipped with Landau closures to the particle-in-cell method
摘要：
粒子池（PIC）方法被成功地用于研究磁化等离子体。然而，这需要大量的计算成本，并限制模拟短的物理运行时间，往往在小于三个空间维度的设置。传统上，这通过混合PIC方法（采用无质量电子）或通过磁流体动力学PIC方法（将背景等离子体建模为单电荷中性磁流体动力学流体）来规避。由于这两种方法都排除了重要的等离子体动力学效应建模，我们引入了一个新的流体PIC代码，耦合一个完全明确的和电荷守恒的多流体求解器的PIC代码SHARP通过电流耦合方案，并解决了全套麦克斯韦方程组。这避免了简化通常采用的欧姆定律，使我们能够完全解决电子的时间和空间尺度，同时保留了多功能性的初始化任意数量的离子，电子，或中性物质的任意速度分布。流体求解器包括封闭模拟朗道阻尼，使我们可以考虑这个重要的动力学过程中，我们的流体物种。我们的流体PIC代码在空间和时间上具有二阶精度。该程序成功地验证了几个测试问题，包括稳定性和准确性的冲击和色散关系和阻尼率的波在非磁化和磁化等离子体。它还匹配的增长率和饱和度的陀螺仪规模和中等规模的不稳定性驱动的漂移带电粒子在磁化的热背景等离子体相比，线性理论和PIC模拟。这个新的流体SHARP代码是专门设计用于研究高能宇宙射线与热等离子体在宏观时间尺度上的相互作用。
英文摘要：
The particle-in-cell (PIC) method is successfully used to study magnetized plasmas. However, this requires large computational costs and limits simulations to short physical run-times and often to setups in less than three spatial dimensions. Traditionally, this is circumvented either via hybrid-PIC methods (adopting massless electrons) or via magneto-hydrodynamic-PIC methods (modelling the background plasma as a single charge-neutral magneto-hydrodynamical fluid). Because both methods preclude modelling important plasma-kinetic effects, we introduce a new fluid-PIC code that couples a fully explicit and charge-conservative multi-fluid solver to the PIC code SHARP through a current-coupling scheme and solve the full set of Maxwell's equations. This avoids simplifications typically adopted for Ohm's Law and enables us to fully resolve the electron temporal and spatial scales while retaining the versatility of initializing any number of ion, electron, or neutral species with arbitrary velocity distributions. The fluid solver includes closures emulating Landau damping so that we can account for this important kinetic process in our fluid species. Our fluid-PIC code is second-order accurate in space and time. The code is successfully validated against several test problems, including the stability and accuracy of shocks and the dispersion relation and damping rates of waves in unmagnetized and magnetized plasmas. It also matches growth rates and saturation levels of the gyro-scale and intermediate-scale instabilities driven by drifting charged particles in magnetized thermal background plasmas in comparison to linear theory and PIC simulations. This new fluid-SHARP code is specially designed for studying high-energy cosmic rays interacting with thermal plasmas over macroscopic timescales.
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