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 set-ups of 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-conserving 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 with 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 time scales.

中文翻译：

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将配备朗道闭包的多流体动力学与细胞内粒子方法耦合

细胞内粒子（PIC）方法已成功用于研究磁化等离子体。然而，这需要大量的计算成本，并将模拟限制为较短的物理运行时间，并且通常限制为小于三个空间维度的设置。传统上，这是通过混合 PIC 方法（采用无质量电子）或磁流体动力学 PIC 方法（将背景等离子体建模为单电荷中性磁流体动力流体）来避免的。由于这两种方法都无法对重要的等离子体动力学效应进行建模，因此我们引入了一种新的流体 PIC 代码，该代码通过电流耦合方案将完全显式且电荷守恒的多流体求解器耦合到 PIC 代码 SHARP，并求解全套麦克斯韦方程组方程。这避免了欧姆定律通常采用的简化，使我们能够完全解析电子的时间和空间尺度，同时保留以任意速度分布初始化任意数量的离子、电子或中性物质的多功能性。流体求解器包括模拟朗道阻尼的闭包，以便我们可以解释流体种类中的这一重要动力学过程。我们的流体-PIC 代码在空间和时间上都是二阶精确的。该代码已成功针对多个测试问题进行了验证，包括冲击的稳定性和准确性以及非磁化和磁化等离子体中波的色散关系和阻尼率。与线性理论和 PIC 模拟相比，它还匹配由磁化热背景等离子体中漂移带电粒子驱动的陀螺尺度和中尺度不稳定性的增长率和饱和水平。这种新的流体 SHARP 代码专门用于研究高能宇宙射线在宏观时间尺度上与热等离子体的相互作用。