Turbulent Heating of Space Plasmas

等离子体是气体被加热到足够高的温度时形成的物质状态，到目前为止是宇宙中普通物质的主要形式。然而，这种等离子体是如何变得如此热的，目前是太空和天体物理学中的主要谜团之一。例如，太阳的日冕，也就是太阳的等离子体大气，比太阳表面热数百倍，但原因尚未确定。理解这种加热对于确定太阳风的起源很重要，太阳风是由于日冕中的高温而从太阳发出的持续快速的等离子体流。此外，太阳风本身被观察到在膨胀到充满太阳系的过程中不断加热。太阳风和日冕以及大多数其他天体物理等离子体都是湍流的，这意味着它们在广泛的尺度上表现出复杂的混乱运动。这些运动可能是观测到的加热的能量来源，但由于之前缺乏高分辨率的现场测量，这种湍流是如何导致加热的确切原因仍有待了解。在接下来的几年里，一系列新的航天器(DSCOVR，太阳探测器Plus，太阳轨道器)将飞越太阳风，以前所未有的高分辨率测量其密度、速度、温度和电磁场等特性。这为研究湍流加热提供了一个独特的机会，因为我们将第一次能够在被认为发生加热的尺度上探测等离子体。在我提出的研究中，我将使用这一新获得的数据来回答一些关键问题，即湍流能量如何导致太阳风和天体物理等离子体的加热。我将通过在测量的太阳风粒子中寻找可能的加热机制的特征信号，确定热量如何相对于湍流产生的结构在等离子体中分布，并测量太阳风中不同类型的粒子如何被不同地加热，从而实现这一点。通过分析来自太阳探测器Plus和太阳轨道器(Solar Orbiter)的数据，在该项目的最后几年，我将调查湍流加热如何在不同的空间环境中运行，以及太阳风如何在接近其起源的地方被加热。这一关于等离子体条件依赖性的信息将允许该结果应用于其他对加热知之甚少的天体物理等离子体，如吸积盘和星系团。这项研究将在伦敦帝国理工学院与欧洲和美国的同事合作进行。尽管这项拟议的研究是基础性的，但其结果可能对几个应用程序具有重要意义，例如空间天气和聚变动力。空间天气是指地球周围空间环境的变化，可能会对整个社会产生重大影响，例如损坏商业卫星、扰乱飞行和干扰地面电力系统。了解由于湍流引起的太阳风的可变性将有助于更准确地预测空间天气。聚变发电使用等离子体来产生可持续的清洁能源，但受到加热等离子体所需的功率以及由于湍流而难以限制的限制。通过研究太空中的湍流并确定等离子体在宇宙中是如何自然加热的，这些知识可以转移到实验室，帮助实现商业聚变动力的目标。

Plasma, the state of matter formed when a gas is heated to sufficiently high temperatures, is by far the dominant form of ordinary matter in the universe. How this plasma gets to be so hot, however, is currently one of the major mysteries in space and astrophysics. For example, the solar corona, the plasma atmosphere of the Sun, is hundreds of times hotter than the Sun's surface, but the reason for this has not yet been established. Understanding this heating is important for determining the origin of the solar wind, the continuous fast stream of plasma emitted from the Sun due to the high temperature in the corona. Furthermore, the solar wind itself is observed to undergo continuous heating as it expands to fill the solar system.The solar wind and solar corona, as well as most other astrophysical plasmas, are turbulent, meaning that they display complex chaotic motions at a broad range of scales. These motions are a possible source of energy for the observed heating, but exactly how this turbulence leads to heating remains to be understood, due to the previous lack of high resolution in situ measurements. In the next few years, a series of new spacecraft (DSCOVR, Solar Probe Plus, Solar Orbiter) will fly through the solar wind, measuring its properties, such as density, velocity, temperature, and electromagnetic fields, in far greater resolution than has ever been achieved before. This offers a unique opportunity to study turbulent heating, since for the first time we will be able to probe the plasma at the scales at which the heating is thought to occur.In my proposed research I will use this newly available data to answer some of the key questions about how turbulent energy leads to the heating of the solar wind and astrophysical plasmas in general. I will do this by looking for the characteristic signatures of the possible heating mechanisms in the measured solar wind particles, determining how the heating is distributed throughout the plasma in relation to the structures generated by the turbulence, and measuring how different types of particle in the solar wind are heated differently. By analysing data from Solar Probe Plus and Solar Orbiter, which will travel far closer to the Sun than ever before, I will investigate, in the later years of the project, how turbulent heating operates in different space environments and how the solar wind is heated close to its origin. This information about the dependence on plasma conditions will allow the results to be applied to other astrophysical plasmas in which heating is poorly understood, such as accretion disks and galaxy clusters. The research will be carried out at Imperial College London, in collaboration with colleagues in Europe and the USA.Although the proposed research is fundamental in nature, the results are potentially important for several applications, for example, space weather and fusion power. Space weather is a term for the changes in the space environment around Earth, which can have a significant impact on society at large, for example, damaging commercial satellites, disrupting flights, and interfering with electrical systems on the ground. Understanding the variability of the solar wind due to turbulence will help contribute to more accurate space weather predictions. Fusion power uses plasmas to generate sustainable clean energy, but is limited by the power needed to heat the plasma, and the difficulty in confining it due to turbulence. By investigating turbulence in space and determining how plasmas are naturally heated in the universe, this knowledge can be transferred to the lab to help achieve the goal of commercial fusion power.