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

布朗1255541湍流发电机过程是从导电流体的湍动流动中产生磁场，例如在地核中发生的情况。了解湍流结构如何产生磁场是发电机研究中的一个中心挑战。然而，由于所需的极端材料特性和规模，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，并且在强烈湍流区域中的流体流动不能被直接模拟。该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，并将实验和低维建模相结合，以了解流体流动结构如何相互作用在发电机中产生磁场。通过设计由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。这样的流体将具有足够高的导电性和磁化率来建造宇宙中最小的湍流发电机(10厘米)。首次同时测量湍流发电机中的流体流动和磁场，以将它们的动力学与设备周围几个位置的温度和磁场探头阵列连接起来。湍流结构可以从这样的测量重建，并用由随机常微分方程组组成的低维模型来模拟。这些实验和建模技术将结合在一起，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，它将通过向更多实验室开放实验研究来改变这一领域--实验规模可以缩小，传统发电机实验中不再需要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，这在传统的发电机实验中是不可能的。在实验发电机中首次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例，用于简单理解和定量预测大型结构在各种湍流中的不同动力学行为。广泛的影响：材料设计将导致开发和表征具有有用的可调特性的流体，包括高导电性和强磁响应；可能的应用包括具有减少散热的磁流变刹车，以及没有移动固体部件的流体动力变压器。天文发电机，如地球和太阳，有着复杂的动力学，还没有被很好地理解。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。地球磁场可以抵御来自太阳的危险辐射。对磁力发电机进行建模可能有助于更好地了解其动力学行为，这可能对航空航天工程产生积极影响。加州大学默塞德分校将为本科生开发一个综合的科学研究教育项目，这是一家为少数族裔服务的研究机构。这包括协调下级和上级实验室课程以及高级论文，重点是科学方法和数据分析。这些教育部分将根据实验室报告、论文和演示文稿的标准进行评估，这些报告、论文和演示文稿符合物理项目的学习目标。

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.