Time-resolved turbulent dynamo in a laser plasma
Time-resolved turbulent dynamo in a laser plasma
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DOI：
10.1073/pnas.2015729118
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发表时间：
2021-03-16
影响因子：
11.1
通讯作者：
Gregori, Gianluca
中科院分区：
文献类型：
--
作者：
Bott, Archie F. A.;Tzeferacos, Petros;Gregori, Gianluca
理解湍流等离子体中磁场的产生和放大对于解释宇宙中磁场的观测至关重要。最近，在低磁普朗特数等离子体（Pm < 1）中的激光装置上进行的实验验证了将这些场的起源和维持归因于所谓的涨落发电机的理论框架。然而，同样的框架提出，波动发电机应不同的操作时，PM & 1，制度相关的许多天体物理环境，如星系团的星系团内介质。本文报道了一个实验室Pm & 1等离子体发电机的研制.我们提供了一个时间分辨的等离子体的演变，测量温度，密度，流速和磁场，这使我们能够探索的各个阶段的波动发电机的操作种子磁场所产生的行动的比尔曼电池机制在初始驱动激光靶相互作用。结构的特征尺度接近随机运动的驱动尺度的磁能被发现增加了近三个数量级，动态饱和。结果表明，这些领域的初始增长发生在一个更大的速度比周转率的驱动规模的随机运动。我们的研究结果指出，强剪切产生的等离子体湍流可以产生更有效地在驱动规模比预期的理想化磁流体动力学（MHD）模拟的非螺旋波动发电机的领域的可能性，这一发现可以帮助解释推断从天体物理系统的观测大规模的领域。
Understanding magnetic-field generation and amplification in turbulent plasma is essential to account for observations of magnetic fields in the universe. A theoretical framework attributing the origin and sustainment of these fields to the so-called fluctuation dynamo was recently validated by experiments on laser facilities in low-magnetic-Prandtl-number plasmas (Pm < 1). However, the same framework proposes that the fluctuation dynamo should operate differently when Pm & 1, the regime relevant to many astrophysical environments such as the intracluster medium of galaxy clusters. This paper reports an experiment that creates a laboratory Pm & 1 plasma dynamo. We provide a time-resolved characterization of the plasma's evolution, measuring temperatures, densities, flow velocities, and magnetic fields, which allows us to explore various stages of the fluctuation dynamo's operation on seed magnetic fields generated by the action of the Biermann-battery mechanism during the initial drive-laser target interaction. The magnetic energy in structures with characteristic scales close to the driving scale of the stochastic motions is found to increase by almost three orders of magnitude and saturate dynamically. It is shown that the initial growth of these fields occurs at a much greater rate than the turnover rate of the driving-scale stochastic motions. Our results point to the possibility that plasma turbulence produced by strong shear can generate fields more efficiently at the driving scale than anticipated by idealized magnetohydrodynamics (MHD) simulations of the nonhelical fluctuation dynamo; this finding could help explain the large-scale fields inferred from observations of astrophysical systems.