Accurately simulating nine-dimensional phase space of relativistic particles in strong fields
Accurately simulating nine-dimensional phase space of relativistic particles in strong fields
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DOI：
10.1016/j.jcp.2021.110367
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发表时间：
2020-07
期刊：
影响因子：
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通讯作者：
Fei Li;V. Decyk;Kyle G. Miller;A. Tableman;F. Tsung;M. Vranic;R. Fonseca;W. Mori
中科院分区：
文献类型：
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作者：
Fei Li;V. Decyk;Kyle G. Miller;A. Tableman;F. Tsung;M. Vranic;R. Fonseca;W. Mori
下一代高功率激光系统，可以集中到超高强度超过10 - 23 W/cm 2，使新的物理制度和应用。这些激光如何与物质相互作用的物理学是高度非线性的，相对论的，并且可能涉及最低阶量子效应。目前用于模拟这些相互作用的工具是粒子细胞（PIC）方法。在强电磁场作用下，带电粒子的运动和自旋受到辐射反应的影响（半经典或量子极限）。标准（PIC）程序通常使用Boris或类似的算子分裂方法来推进标准相空间中的粒子。这些方法已被证明需要非常小的时间步长在强场制度，以获得准确的结果。此外，一些问题需要跟踪粒子的自旋，这会创建一个九维（9D）粒子相空间，即（x，u，s）。因此，需要能够在强场区域（其中自旋和动量演化都受到辐射反应的影响）中对9D相空间进行高保真建模的数值算法。我们提出了一种新的粒子推进器，工作在9D和6D相空间（即，有和没有自旋）的基础上分析，而不是跳跃式解决方案的动量和自旋推进洛伦兹力，连同半经典形式的辐射反应的Landau-Lifshitz方程和自旋演化的Bargmann-Michel-Telegdi方程。位置提前的解析解也得到了，但这些是不服从交错的空间和时间在标准PIC代码。这些解析解是通过假设一个局部均匀和恒定的电磁场在一个时间步长。该解决方案提供了9D相空间的粒子的适当的时间方面的进步，和映射被用来确定适当的时间步长持续时间为每个粒子作为实验室帧的时间步长的函数。由于粒子轨道和自旋轨道的解析积分，可以大大减少在超高场中求解轨道所需的时间步长的限制。PIC代码中用于精确推进字段所需的时间步长可以提供附加约束。我们提出了单粒子模拟表明，建议的粒子推进器可以大大提高粒子轨迹的精度在6D或9D相空间给定的激光场。我们已经实现了新的推杆到PIC代码奥西里斯。示例仿真表明，所提出的推杆提供了一个给定的时间步长的改进。还讨论了所提出的推杆的数值效率。
Next-generation high-power laser systems that can be focused to ultra-high intensities exceeding 10 23 W/cm 2 are enabling new physics regimes and applications. The physics of how these lasers interact with matter is highly nonlinear, relativistic, and can involve lowest-order quantum effects. The current tool of choice for modeling these interactions is the particle-in-cell (PIC) method. In the presence of strong electromagnetic fields, the motion of charged particles and their spin is affected by radiation reaction (either the semi-classical or the quantum limit). Standard (PIC) codes usually use Boris or similar operator-splitting methods to advance the particles in standard phase space. These methods have been shown to require very small time steps in the strong-field regime in order to obtain accurate results. In addition, some problems require tracking the spin of particles, which creates a nine-dimensional (9D) particle phase space, ie,(x, u, s). Therefore, numerical algorithms that enable high-fidelity modeling of the 9D phase space in the strong-field regime (where both the spin and momentum evolution are affected by radiation reaction) are desired. We present a new particle pusher that works in 9D and 6D phase space (ie, with and without spin) based on analytical rather than leapfrog solutions to the momentum and spin advance from the Lorentz force, together with the semi-classical form of radiation reaction in the Landau-Lifshitz equation and spin evolution given by the Bargmann-Michel-Telegdi equation. Analytical solutions for the position advance are also obtained, but these are not amenable to the staggering of space and time in standard PIC codes. These analytical solutions are obtained by assuming a locally uniform and constant electromagnetic field during a time step. The solutions provide the 9D phase space advance in terms of a particle's proper time, and a mapping is used to determine the proper time step duration for each particle as a function of the lab frame time step. Due to the analytical integration of particle trajectory and spin orbit, the constraint on the time step needed to resolve trajectories in ultra-high fields can be greatly reduced. The time step required in a PIC code for accurately advancing the fields may provide additional constraints. We present single-particle simulations to show that the proposed particle pusher can greatly improve the accuracy of particle trajectories in 6D or 9D phase space for given laser fields. We have implemented the new pusher into the PIC code Osiris. Example simulations show that the proposed pusher provides improvement for a given time step. A discussion on the numerical efficiency of the proposed pusher is also provided.