Production of Magnetic Turbulence by Cosmic Rays Drifting Upstream of Supernova Remnant Shocks
Production of Magnetic Turbulence by Cosmic Rays Drifting Upstream of Supernova Remnant Shocks
复制标题
漂移到超新星遗迹激波上游的宇宙射线产生磁湍流
DOI：
10.1086/590054
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发表时间：
2008
期刊：
影响因子：
--
通讯作者：
K. Nishikawa
中科院分区：
文献类型：
--
作者：
J. Niemiec;M. Pohl;T. Stroman;K. Nishikawa
我们提出了由向超新星遗迹激波上游漂移的各向同性宇宙射线离子产生的磁湍流的二维和三维细胞内粒子模拟的结果。这些研究旨在测试最近对短波长磁场强烈放大的预测，并研究磁湍流的后续演化及其对宇宙线轨迹的反作用。对于我们的参数，倾斜丝状模式比在极限 ω ≪ Ωi 下分析发现的非共振平行模式增长得更快，并且增长速率比平行平面波模式的估计慢。当结构已经是各向同性时，MHD 模拟中还观察到演化的倾斜丝状模式在非线性相中占主导地位。因此，我们证实了由于上游等离子体中宇宙线离子的漂移而产生了湍流磁场，但我们的主要结果发现，湍流的幅度在δB/B∼1左右饱和。磁湍流对粒子的反反应导致宇宙线和背景介质的总体流速对齐，这解释了在中等磁场幅度下不稳定性的饱和。先前发表的MHD模拟假设宇宙线电流恒定，宇宙线中没有能量或动量通量，这排除了产生的磁场对宇宙线的反反应，从而人为地抑制了场振幅的饱和。这可以解释 MHD 模拟中磁场的持续增长。强磁场放大到振幅 δB ≫ B0 尚未得到证实。
We present results of two- and three-dimensional particle-in-cell simulations of magnetic turbulence production by isotropic cosmic-ray ions drifting upstream of supernova remnant shocks. The studies aim at testing recent predictions of a strong amplification of short-wavelength magnetic field and at studying the subsequent evolution of the magnetic turbulence and its back-reaction on cosmic-ray trajectories. For our parameters an oblique filamentary mode grows more rapidly than nonresonant parallel modes analytically found in the limit ω ≪ Ωi, and the growth rate is slower than is estimated for the parallel plane wave mode. The evolved oblique filamentary mode was also observed in MHD simulations to dominate in the nonlinear phase, when the structures are already isotropic. We thus confirm the generation of the turbulent magnetic field due to the drift of cosmic-ray ions in the upstream plasma, but as our main result find that the amplitude of the turbulence saturates at about δB/B ∼ 1. The back-reaction of the magnetic turbulence on the particles leads to an alignment of the bulk flow velocities of the cosmic rays and the background medium, which accounts for the saturation of the instability at moderate amplitudes of the magnetic field. Previously published MHD simulations have assumed a constant cosmic-ray current and no energy or momentum flux in the cosmic rays, which excludes a back-reaction of the generated magnetic field on cosmic rays, and thus the saturation of the field amplitude is artificially suppressed. This may explain the continued growth of the magnetic field in the MHD simulations. A strong magnetic field amplification to amplitudes δB ≫ B0 has not been demonstrated yet.