Laboratory Simulation of Magnetized Plasma Turbulence in the Intergalactic Medium

我们提出了一个实验计划来探索现代天体物理学中最大的谜题之一：宇宙中无处不在的磁场的产生和放大。目的是通过紊流发电机证明磁场的放大——这是现代实验等离子体物理学的一个巨大挑战。我们还将研究湍流能量在速度、磁场和密度波动之间的分布，为湍流等离子体中的能量级联提供一个全面的实验表征。磁场在宇宙中无处不在。它们的能量密度与平均等离子体流的能量密度相当，因此磁场在发光物质的动力学中是必不可少的参与者。总磁能代表了宇宙能量预算中相当大的一部分。这些场的起源是什么？它们无处不在、随机且动态强大的事实表明，一种普遍的物理机制在起作用。关于宇宙磁发生的最流行的设想是，磁场通过某种形式的湍流发电机增长——通过嵌入其中的湍流运动快速（指数）放大随机场，从最初的小种子开始。理解磁发生是理解宇宙湍流的更广泛挑战的一部分，以及不同形式的能量（热、湍流、磁）在不同尺度上的划分方式。随着高功率激光器的出现，一个新的研究领域已经打开，使用简单的缩放关系，可以在实验室中重现天体物理环境。这种相似性足以使这种实验引起人们的高度兴趣。在这里，我们建议建立一个实验平台，利用激光产生的等离子体，磁场产生和湍流放大。在动荡的等离子体中，小磁场最初是由密度和温度梯度不一致的电流产生的，这就是所谓的比尔曼电池效应。通过描述这些等离子体和嵌入磁场的特性，我们打算表明这些微小的磁场可以被放大到更大的值，并且可以与湍流运动的动能均分。我们将利用这些实验来测量湍流等离子体中的磁能、密度和速度谱，从而解决能量级联的细节。因此，我们的工作将首次在实验上建立理论期望的合理性，即在宇宙学上短的时间内，原星系结构（~10^-21 G）产生的微小种子可以被放大到观测到动态显著值（~10^-6 G）。

We propose an experimental programme to probe one of the greatest puzzles of modern astrophysics: the generation and amplification of magnetic fields ubiquitously found in the Universe. The aim is to demonstrate amplification of magnetic fields by turbulent dynamo - a great challenge of modern experimental plasma physics. We will also study the distribution of turbulent energy between velocity, magnetic and density fluctuations, providing a comprehensive experimental characterisation of the energy cascade in a turbulent plasma. Magnetic fields are ubiquitously observed in the Universe. Their energy density is comparable to the energy density of the mean plasma flows, so the magnetic fields are essential players in the dynamics of the luminous matter. The total magnetic energy represents a sizable fraction of the cosmic energy budget. What is the origin of these fields? The fact that they are ubiquitous, stochastic and dynamically strong suggests that a universal physical mechanism is at play. The most popular scenario of the cosmic magnetogenesis is that the field grows via some form of turbulent dynamo - fast (exponential) amplification of stochastic field by turbulent motions into which it is embedded, starting from an initial small seed. Understanding magnetogenesis is part of the broader challenge of understanding cosmic turbulence, and the way different form of energies (thermal, turbulent, magnetic) are partitioned on various scales.With the advent of high-power lasers, a new field of research has opened where, using simple scaling relations, astrophysical environments can be reproduced in the laboratory. The similarity is sufficiently close to make such experiments of high interest. Here we propose to establish an experimental platform using laser-produced plasmas where magnetic fields are produced and amplified by turbulence. In the turbulent plasma, small magnetic fields are initially generated by electrical currents resulting from mis-aligned density and temperature gradients - the so-called Biermann battery effect. By then characterizing the properties of such plasmas and the embedded magnetic fields, we intend to show that those tiny fields can be amplified to much larger values, and up to equipartition with the kinetic energy of the turbulent motions. We will use these experiments to measure the magnetic-energy, density and velocity spectra in the turbulent plasma, thus addressing the details of the energy cascade. Thus, our work would establish, for the first time experimentally, the soundness of the theoretical expectation that tiny seeds produced at protogalactic structures (~10^-21 G) can be amplified to observed dynamically significant values (~10^-6 G) in cosmologically short times.