克服等离子体加速的增强帧Particle-In-Cell模拟中的时间步长限制
Overcoming timestep limitations in boosted-frame Particle-In-Cell simulations of plasma-based acceleration
摘要：
显式电磁粒子单元（PIC）代码通常受到Courant-Friedrichs-Lewy（CFL）条件的限制，这意味着乘以光速的时间步长必须小于最小单元尺寸。在基于等离子体的加速的增强帧PIC模拟的情况下，这种限制可能是一个主要的障碍，因为单元通常沿着纵向方向非常细长，并且时间步长因此受到小的横向单元尺寸的限制。这需要许多小时间步长的PIC迭代，并且可以限制提升帧技术的潜在加速。在这里，通过使用CFL-免费的解析谱求解器，并通过减轻额外的数值不稳定性，在大的时间步长，我们表明，它是可以克服传统的时间步长的限制，从而实现在更广泛的参数范围内的提升帧技术的全部潜力。
英文摘要：
Explicit electromagnetic Particle-In-Cell (PIC) codes are typically limited by the Courant- Friedrichs-Lewy (CFL) condition, which implies that the timestep multiplied by the speed of light must be smaller than the smallest cell size. In the case of boosted-frame PIC simulations of plasma-based acceleration, this limitation can be a major hinderance as the cells are often very elongated along the longitudinal direction and the timestep is thus limited by the small, transverse cell size. This entails many small-timestep PIC iterations, and can limit the potential speed-up of the boosted-frame technique. Here, by using a CFL-free analytical spectral solver, and by mitigating additional numerical instabilities that arise at large timestep, we show that it is possible to overcome traditional limitations on the timestep and thereby realize the full potential of the boosted-frame technique over a much wider range of parameters.
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