CAREER: Large-Scale Structures in Turbulent Dynamo Experiments with Liquid-Metal Suspensions

紊流发电机过程是由导电流体的紊流产生磁场；比如地核。了解湍流结构如何产生磁场是发电机研究中的一个核心挑战。然而，由于极端的材料特性和所需的规模，只有一个实验能够产生湍流发电机；即使在这种情况下，产生磁场的流体流动还没有被测量到，而且在强湍流状态下，流体流动也不能直接模拟。本研究计划的目标是利用材料设计开发一种革命性的磁流体动力学实验方法，并将实验与低维建模相结合，以了解流体流动结构如何相互作用以产生发电机中的磁场。通过设计悬浮在液态金属中的磁性颗粒组成的材料，即悬浮在液态镓及其合金中的微米级铁颗粒，可以达到在实验室中产生湍流发电机所需的极端参数范围。这种流体将具有足够高的导电性和磁化率，可以建造宇宙中最小的湍流发电机（10厘米）。将首次同时测量紊流发电机中的流体流动和磁场，并将其动力学与设备周围几个位置的温度和磁场探头阵列联系起来。湍流结构可以从这些测量中重建，并用由随机常微分方程组成的低维模型建模。这些实验和建模技术将结合起来，以了解湍流结构如何相互作用产生磁场。智力优势：这种材料设计是发电机的一种新方法，它将通过向更多的实验室开放实验研究来改变该领域——实验可以按比例缩小，并且在传统的发电机实验中无需大型设施来处理液态钠。悬架的可调材料特性将允许在相同参数范围内与模拟进行直接比较，这是传统发电机实验无法实现的。首次在实验发电机中同时测量湍流结构和磁场将允许开发和测试湍流结构如何产生磁场的模型。低维建模技术有可能成为一种新的范式，用于简单理解和定量预测各种湍流中大型结构的不同动力学行为。更广泛的影响：材料设计将导致具有有用可调特性的流体的开发和表征，包括高导电性和强磁响应；可能的应用包括减少散热的磁流变制动器，以及没有移动固体部件的流体动力变压器。像地球和太阳这样的天文发电机具有复杂的动力学，目前还没有得到很好的理解。太阳耀斑会干扰长波无线电通信，并对航天器产生辐射危害。地球的磁场可以防止来自太阳的危险辐射。磁发电机的建模可以更好地理解其动力学行为，这可能对航空航天工程产生积极的影响。加州大学默塞德分校是一个为少数民族服务的研究机构，将为本科生开发一个综合科研教育项目。这包括协调低年级和高年级的实验课程和高级论文，重点是科学方法和数据分析。这些教育组成部分将根据实验室报告、论文和符合物理课程学习目标的演示文稿的标准进行评估。

Brown1255541The turbulent dynamo process is the generation of a magnetic field from the turbulent flow of a conducting fluid; which occurs for example in the Earth's core. An understanding of how turbulent flow structures generate the magnetic field is a central challenge in dynamo research. However, only one experiment has been able to produce a turbulent dynamo because of the extreme material properties and scale required; even in that case the fluid flows that generate the magnetic field have not yet been measured, and the fluid flows cannot be directly simulated in the strongly turbulent regime. The goals of this research plan are to use materials design to develop a revolutionary approach to magnetohydrodynamic experiments, and combine experiments and low-dimensional modeling to understand how fluid flow structures interact to generate magnetic fields in dynamos. The extreme parameter regime required for generating a turbulent dynamo in the laboratory will be reached by designing materials consisting of magnetic particles suspended in a liquid metal, i.e. micron-sized iron particles suspended in liquid gallium and its alloys. Such a fluid will have a high enough conductivity and magnetic susceptibility to build the universe's smallest turbulent dynamo (10 cm). The first simultaneous measurements of fluid flow and magnetic field in a turbulent dynamo will be made to connect their dynamics with an array of temperature and magnetic field probes at several locations around the apparatus. Turbulent flow structures can be reconstructed from such measurements, and modeled with low-dimensional models consisting of stochastic ordinary differential equations. These experimental and modeling techniques will be combined to understand how turbulent flow structures interact to produce magnetic fields. Intellectual merit: This materials design is a novel approach to dynamos that would transform the field by opening up experimental research to more laboratories -- experiments could be scaled down and the need for large facilities to handle liquid sodium in traditional dynamo experiments would be eliminated. The tunable material properties of suspensions will allow for a direct comparison with simulations in the same parameter regime which has not been possible with traditional dynamo experiments. The first simultaneous measurements of turbulent flow structures and magnetic fields in an experimental dynamo will allow development and testing of models for how turbulent flow structures generate a magnetic field. The low-dimensional modeling techniques have the potential to become a new paradigm for simple understanding and quantitative predictions of different dynamical behaviors of large-scale structures in a wide variety of turbulent flows.Broader impacts: Materials design will result in the development and characterization of fluids with useful tunable properties including high conductivity and a strong magnetic response; possible applications include magnetorheological brakes with reduced heat dissipation, and fluid power transformers with no moving solid parts. Astronomical dynamos such as the Earth and Sun have complicated dynamics that are not well-understood. Solar flares can interfere with long-wave radio communications and produce radiation hazards to spacecraft. Earth's magnetic field protects against dangerous radiation from the Sun. Modeling of magnetic dynamos may lead to better understanding of their dynamical behavior, which could have a positive impact on aerospace engineering. An integrated scientific research education program for undergraduates will be developed at UC Merced, a minority-serving research institution. This includes coordination of the lower division and upper division laboratory courses, and senior theses, with a focus on the scientific method and data analysis. These educational components will be evaluated according to a rubric for laboratory reports, theses, and presentations in line the physics program's learning objectives.