Magnetic Reconnection as a Universal Plasma Process: Investigating Onset, Energy Release and Particle Acceleration

磁重联是一个普遍的和基本的等离子体过程，在磁场和等离子体本身之间传递能量和动量。它发生在各种各样的情况下-在行星磁层中，它是磁暴的原因，在太阳和恒星大气中，它会引起耀斑，并且它被认为在一些天体物理现象中很重要，例如活动星系核，太阳黑子，伽马射线爆发和磁星。理解磁场重联也具有实际重要性，因为它是空间天气核心的关键物理过程之一[伊斯特伍德，菲尔。横河Soc. A，in press，2008]。因此，这个建议有助于回答STFC的科学问题“太阳如何影响地球？”到达地球的高能粒子的来源和性质是什么？关键目标：问题1：何时以及如何触发重新连接？为了最终预测爆炸性的重连事件，如太阳和恒星耀斑，亚暴和其他天体物理现象，有必要了解重连是如何触发的。我将使用在地球的磁尾重联发病的原位航天器观测回答的关键问题，它是否主要是由本地不稳定性或外部驱动控制。问题2：是什么控制着重连的结构和动力学？行星磁层和恒星日冕中的磁场重联通常是突发性的，而太阳风中的重联可以在大尺度上持续很长时间。我将比较新的和存档的观测磁尾的遥远的X线（中间重联制度），以确定何时以及为什么重联是突发或准稳定。我还将使用多点观测来测试非对称重联的新理论。问题三：慢激波在磁场重联中的作用附着在中心扩散区的慢激波是快速重联的关键部分。最近，在太阳风中发现了重联，其条件非常适合于慢激波的形成;我们的初步研究证实了慢激波的存在。我将在所有可用的航天器观测中识别和检查太阳风重连事件，并进行统计研究，以首次全面评估其发生率和详细的实验性质。问题4：重联如何产生高能粒子？通过重联产生高能粒子，特别是电子，是等离子体物理中一个尚未解决的主要问题。有几种不同的理论可以解释这种情况是如何发生的。通过研究磁尾中的重联，在磁亚暴期间产生高能粒子，我将使用磁尾观测来确定统计粒子加速发生在重联期间，并建立不同的机制往往占主导地位。研究将在哪里以及如何进行：这项研究将在帝国理工学院进行，因为它在观察空间等离子体方面具有优势，而且该项目的成功取决于与跨学科的广泛研究人员合作的机会。我将通过分析各种航天器在不同空间区域进行的实地观测来解决这些问题。我将与马里兰州大学和特拉华州大学的等离子体模拟小组合作，他们分别从事重新连接的研究。模拟结果将用于为数据分析提供信息，数据将用于发展理论。这项研究还将涉及与特定使命小组的合作，特别是与集群、立体声和THEMIS的合作。

Principal subject of the research: Magnetic reconnection is a universal and fundamental plasma process that transfers energy and momentum between the magnetic field and the plasma itself. It occurs in a wide variety of circumstances - in planetary magnetospheres it is responsible for magnetic storms, in solar and stellar atmospheres it causes flares, and it is thought to be important in several astrophysical phenomena such as active galactic nuclei, pulsars, gamma ray bursts and magnetars. Understanding magnetic reconnection is also of practical importance since it is one of the key physical processes at the heart of space weather [Eastwood, Phil. Trans. R. Soc. A, in press, 2008]. As such, this proposal helps answer the STFC science questions 'How does the Sun affect the Earth?' and 'What are the origins and properties of the energetic particles reaching the Earth?' Key aims: Question 1: When and how is reconnection triggered? To ultimately predict explosive reconnection events such as solar and stellar flares, substorms and other astrophysical phenomena, it is necessary to understand how reconnection is triggered. I will use in-situ spacecraft observations of reconnection onset in the Earth's magnetotail to answer the key question of whether it is controlled mainly by local instabilities or external driving. Question 2: What controls the structure and dynamics of reconnection? Magnetic reconnection in planetary magnetospheres and stellar coronae is typically bursty whereas reconnection in the solar wind can persist over large scales for long times. I will compare new and archived observations of the magnetotail's distant X-line (an intermediate reconnection regime) to determine when and why reconnection is either bursty or quasi-steady. I will also use multi-point observations to test new theories of asymmetric reconnection. Question 3: The role of slow shocks in magnetic reconnection Slow shocks attached to the central diffusion region are a crucial part of fast reconnection. Recently, reconnection has been discovered in the solar wind, under conditions that are ideal for slow shock formation; our preliminary study has confirmed the existence of slow shocks. I will identify and examine the solar wind reconnection events in all available spacecraft observations and perform a statistical study to fully evaluate their occurrence rate and detailed experimental properties for the first time. Question 4: How does reconnection produce energetic particles? The generation of energetic particles by reconnection, especially electrons, is a major unsolved problem in plasma physics. Several different theories have been developed to explain how this occurs. By examining reconnection in the magnetotail, where energetic particles are generated during magnetic substorms, I will use magnetotail observations to determine statistically where particle acceleration occurs during reconnection and establish when different mechanisms tend to dominate. Where and how the research would be undertaken: The research will be undertaken at Imperial College because of its strength in observing space plasmas and because the success of the project depends on the opportunity to work with a wide range of researchers across disciplines. I will address these questions by analysing observations made in situ by a variety of spacecraft in different regions of space. Who else would be involved I will work in collaboration with plasma simulation groups at the University of Maryland and the University of Delaware who are engaged in separately funded studies of reconnection. Results from simulations will be used to inform the analysis of the data, and data will be used to develop theory. This research will also involve collaboration with mission specific teams, in particular Cluster, STEREO and THEMIS.