Similarity of magnetized plasma wake channels behind relativistic laser pulses with different wavelengths
Similarity of magnetized plasma wake channels behind relativistic laser pulses with different wavelengths
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不同波长相对论性激光脉冲背后磁化等离子体尾流通道的相似性
DOI：
10.1016/j.cpc.2019.07.004
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发表时间：
2019
影响因子：
6.3
通讯作者：
and A. S. Pirozhkov
中科院分区：
文献类型：
--
作者：
A. Bierwage;T. Zh Esirkepov;J. K. Koga;and A. S. Pirozhkov
通过在存在外部磁场的情况下对相对论性激光等离子体尾迹进行细胞内粒子模拟，我们证明存在一个参数窗口，其中磁化尾迹通道的动态在很大程度上与激光波长 λ las 无关。这种“有限相似性”表现的一个条件是电子密度ne高度亚临界，因此等离子体不会影响激光。自由选择方便的激光波长对于实验和模拟非常有用。在模拟中，放大的波长（因此，更粗的网格和更大的时间步长）减少了计算工作量，而有限的相似性确保了尾流通道的整体结构和演化阶段得以保留。在我们的演示示例中，我们从 CO 2 激光器发出的太瓦·皮秒脉冲开始，λ las= 10 μ m，其场在亚毫米大小的焦斑中心达到相对论振幅。在存在特斯拉级磁场的情况下，激光被射入稀疏的氘气 (ne∼ 1 0 13 cm− 3)。在 4 μ m≤ λ las≤ 40 μ m 的 2D 中证明了有限的相似性，并且预计会扩展到更短的波长。假设这种有限的相似性在 3D 中也成立，将波长增加到 40 μm 使我们能够模拟尾流通道的余辉动力学一直到纳秒范围。
Using particle-in-cell simulations of relativistic laser plasma wakes in the presence of an external magnetic field, we demonstrate that there exists a parameter window where the dynamics of the magnetized wake channel are largely independent of the laser wavelength λ las. One condition for this manifestation of “limited similarity” is that the electron density n e is highly subcritical, so that the plasma does not affect the laser. The freedom to choose a convenient laser wavelength can be useful in experiments and simulations. In simulations, an up-scaled wavelength (and, thus, a coarser mesh and larger time steps) reduces the computational effort, while limited similarity ensures that the overall structure and evolutionary phases of the wake channel are preserved. In our demonstrative example, we begin with a terrawatt⋅ picosecond pulse from a CO 2 laser with λ las= 10 μ m, whose field reaches a relativistic amplitude at the center of a sub-millimeter-sized focal spot. The laser is shot into a sparse deuterium gas (n e∼ 1 0 13 cm− 3) in the presence of a tesla-scale magnetic field. Limited similarity is demonstrated in 2D for 4 μ m≤ λ las≤ 40 μ m and is expected to extend to shorter wavelengths. Assuming that this limited similarity also holds in 3D, increasing the wavelength to 40 μ m enables us to simulate the after-glow dynamics of the wake channel all the way into the nanosecond regime.