Turbulence in fluids is a ubiquitous, fascinating, and complex natural phenomenon that is not yet fully understood. Unraveling turbulence in high density, high temperature plasmas is an even bigger challenge because of the importance of electromagnetic forces and the typically violent environments. Fascinating and novel behavior of hot dense matter has so far been only indirectly inferred because of the enormous difficulties of making observations on such matter. Here, we present direct evidence of turbulence in giant magnetic fields created in an overdense, hot plasma by relativistic intensity (1018W/cm2) femtosecond laser pulses. We have obtained magneto-optic polarigrams at femtosecond time intervals, simultaneously with micrometer spatial resolution. The spatial profiles of the magnetic field show randomness and their k spectra exhibit a power law along with certain well defined peaks at scales shorter than skin depth. Detailed two-dimensional particle-in-cell simulations delineate the underlying interaction between forward currents of relativistic energy “hot” electrons created by the laser pulse and “cold” return currents of thermal electrons induced in the target. Our results are not only fundamentally interesting but should also arouse interest on the role of magnetic turbulence induced resistivity in the context of fast ignition of laser fusion, and the possibility of experimentally simulating such structures with respect to the sun and other stellar environments.
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机译:流体中的湍流是一种普遍存在的,令人着迷的,复杂的自然现象,目前尚未完全了解。由于电磁力的重要性和典型的暴力环境,在高密度,高温等离子体中消除湍流是一个更大的挑战。迄今为止,由于对热致密物质进行观测的巨大困难,只能间接地推断出其令人着迷的新颖行为。在这里,我们提供飞秒激光脉冲的相对论强度(10 18 sup> W / cm 2 sup>)在超密度热等离子体中产生的巨大磁场中湍流的直接证据。我们已经获得了飞秒时间间隔的磁光极化图,同时具有微米级的空间分辨率。磁场的空间分布显示出随机性,并且它们的k谱显示出幂律,并且在比趋肤深度更短的尺度上具有某些明确定义的峰值。详细的二维单元中粒子模拟描述了由激光脉冲产生的相对论能量“热”电子的正向电流与靶中感应的热电子的“冷”返回电流之间的潜在相互作用。我们的结果不仅从根本上是有趣的,而且还应该引起人们的兴趣,即在激光聚变的快速点火环境中磁湍流感应电阻率的作用,以及就太阳和其他恒星环境进行实验模拟此类结构的可能性。
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