Simulations of Laser Experiments to Study the Origin of Cosmic Magnetic Fields

模拟激光实验研究宇宙磁场的起源

基本信息

批准号：
1619573
负责人：
Petros Tzeferacos
金额：
$ 1.5万
依托单位：
University of Chicago
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2016
资助国家：
美国
起止时间：
2016-08-15 至 2019-07-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1619573&HistoricalAwards=false
关键词：
Simulations Laser Experiments Study Origin

项目摘要

Magnetic fields are ubiquitous in the universe. However, their origin is not fully understood. While cosmologists and astrophysicists have proposed a variety of ways in which small seed magnetic fields could be created, the significantly larger values of cosmic magnetic fields we observe are believed to be the result of the amplification of these seed fields by a turbulent flow of plasma, the so-called turbulent dynamo mechanism. This mechanism has not yet been demonstrated in a controlled laboratory environment. Experiments to demonstrate and study turbulent dynamo in the laboratory are now being planned using the high-intensity lasers at the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory and the Laser Megajoule (LMJ) facility in France - the two largest laser facilities in the world. The effort supported by this award consists of designing and modeling these highly demanding experiments through simulation campaigns using a highly capable code to run large-scale 3D simulations. The simulations are vital to ensuring the experiments achieve the conditions required for the turbulent dynamo mechanism to operate and are crucial to interpreting the results of the experiments. This work will further the transformation of the academic community's ability to design and analyze High Energy Density Physics experiments at large laser facilities and will train junior scientists to design and interpret such experiments using validated simulations - a critical national need.The experiments to be modeled build on pathfinder experiments that have been conducted on the Vulcan laser at the Rutherford-Appleton Laboratory in the UK and the Omega laser at Laboratory for Laser Energetics at the University of Rochester. They also build on the experience that has been gained designing and interpreting these experiments using validated simulations done with the FLASH code, a highly capable radiation-MHD code developed by the group. The configurations to be used for the NIF and LMJ experiments are based on the platform deployed for the Omega laser, adapted for the large laser facilities using FLASH simulations. The NIF experiment will probe dynamo in the regime of large magnetic Prandtl numbers, the ratio of magnetic-to-fluid Reynolds numbers (Pm = Rm / Re 1), while the LMJ experiment will focus on magnetic field amplification for Pm 1. The dynamo mechanism is expected to operate differently in each regime and FLASH simulations will ensure the experiments reach the required plasma states. These experiments promise to characterize the distribution of turbulent energy among the velocity, magnetic field, and density fluctuations, providing a comprehensive picture of the energy cascade in a magnetized, turbulent plasma. Since the number of laser shots per shot day is only two at NIF and three at LMJ, there is no room for error: numerical modeling to design and analyze the experiments is imperative to accomplish the scientific goals of demonstrating and characterizing the turbulent dynamo mechanism.

磁场在宇宙中无处不在。然而，它们的起源尚不完全清楚。虽然宇宙学家和天体物理学家提出了多种创建小种子磁场的方法，但我们观察到的宇宙磁场的显着较大值被认为是等离子体湍流放大这些种子场的结果，所谓的湍流发电机机制。该机制尚未在受控实验室环境中得到证实。目前正在计划使用劳伦斯利弗莫尔国家实验室国家点火装置 (NIF) 和法国百万焦耳激光 (LMJ) 设施（法国最大的两个激光设施）的高强度激光器，在实验室中演示和研究湍流发电机。世界。该奖项支持的工作包括通过使用功能强大的代码运行大规模 3D 模拟的模拟活动来设计和建模这些高要求的实验。模拟对于确保实验达到湍流发电机机构运行所需的条件至关重要，并且对于解释实验结果也至关重要。这项工作将进一步提高学术界在大型激光设施中设计和分析高能量密度物理实验的能力，并将培训初级科学家使用经过验证的模拟来设计和解释此类实验——这是国家的一项关键需求。英国卢瑟福-阿普尔顿实验室的 Vulcan 激光器和罗彻斯特大学激光能量学实验室的 Omega 激光器进行了探路者实验。他们还利用通过 FLASH 代码（该小组开发的一种高性能辐射 MHD 代码）完成的经过验证的模拟来设计和解释这些实验所获得的经验。用于 NIF 和 LMJ 实验的配置基于为 Omega 激光器部署的平台，适用于使用 FLASH 模拟的大型激光设施。 NIF 实验将在大磁普朗特数、磁流体雷诺数之比 (Pm = Rm / Re 1) 范围内探测发电机，而 LMJ 实验将重点关注 Pm 1 的磁场放大。预计机制在每种状态下的运行方式不同，FLASH 模拟将确保实验达到所需的等离子体状态。这些实验有望表征湍流能量在速度、磁场和密度波动之间的分布，提供磁化湍流等离子体中能量级联的全面图像。由于 NIF 每天的激光发射次数仅为 2 次，LMJ 每天的激光发射次数仅为 3 次，因此不存在任何误差的余地：设计和分析实验的数值模型对于实现演示和表征湍流发电机机制的科学目标至关重要。