Turbulent amplification of magnetic fields in laboratory laser-produced shock waves
Turbulent amplification of magnetic fields in laboratory laser-produced shock waves
复制标题
DOI：
10.1038/nphys2978
复制
发表时间：
2014-07-01
期刊：
影响因子：
19.6
通讯作者：
Gregori, G.
中科院分区：
文献类型：
--
作者：
Meinecke, J.;Doyle, H. W.;Gregori, G.
对超新星遗迹仙后座 A 的 X 射线 (1-3) 和射电 (4-6) 观测表明，其磁场比周围星际介质中的磁场强约 100 倍。与外部激波一致的场可能是通过涉及宇宙射线的非线性反馈过程产生的(2,7,8)。遗迹内部大磁场的起源尚不清楚，但可能是由于湍流运动而被拉伸和放大的。超新星喷射物与星周气体之间接触不连续处的流体动力学不稳定性可能会产生湍流(9)。然而，仙后座 A 的光学观测表明，喷射物与超新星爆炸前形成的高度不均匀、致密的星周云库相互作用(10-12)。在此，我们研究了当外部激波超过环境介质中的致密团块时引起湍流放大的可能性(13-15)。我们报告的实验室实验表明，当冲击与塑料网格相互作用时，磁场会被放大。我们表明，我们的实验结果可以解释在遗迹内部观察到的同步加速器发射。该实验还提供了等离子体湍流磁场放大的实验室示例，这是一种被认为发生在许多天体物理现象中的物理过程。
X-ray(1-3) and radio(4-6) observations of the supernova remnant Cassiopeia A reveal the presence of magnetic fields about 100 times stronger than those in the surrounding interstellar medium. Field coincident with the outer shock probably arises through a nonlinear feedback process involving cosmic rays(2,7,8). The origin of the large magnetic field in the interior of the remnant is less clear but it is presumably stretched and amplified by turbulent motions. Turbulence may be generated by hydrodynamic instability at the contact discontinuity between the supernova ejecta and the circumstellar gas(9). However, optical observations of Cassiopeia A indicate that the ejecta are interacting with a highly inhomogeneous, dense circumstellar cloud bank formed before the supernova explosion(10-12). Herewe investigate the possibility that turbulent amplification is induced when the outer shock overtakes dense clumps in the ambient medium(13-15). We report laboratory experiments that indicate the magnetic field is amplified when the shock interacts with a plastic grid. We show that our experimental results can explain the observed synchrotron emission in the interior of the remnant. The experiment also provides a laboratory example of magnetic field amplification by turbulence in plasmas, a physical process thought to occur in many astrophysical phenomena.