Fundamental Wave-Plasma Processes

地球的磁场形状与简单的条形磁铁产生的磁场非常相似。磁力线从行星的一个磁极出现，并从大气层延伸出数千公里进入太空，然后返回到另一个半球的磁极。而不是真空，这些场线通过的空间区域充满了等离子体/由带电粒子组成的导电气体。这些粒子大多起源于地球大气，由紫外线阳光产生，使高海拔大气中的气体电离，这一区域被称为电离层。太阳也有很强的磁场。当核过程在太阳内部产生能量时，太阳大气的外层通过太阳系向外扩展，形成太阳风。当太阳风到达地球时，它会与行星的磁场相撞，并绕着行星转。地球磁场从太阳风中挖出的空穴被称为磁层。在磁层内部，等离子体和磁场通常主要来自地球。在磁层之外，它们起源于太阳。这些区域并不总是严格分开的，这导致了我们的行星与其最近的恒星之间的电磁相互作用。电离层对通过它的无线电波有重大影响，而一些源自太阳风的高能粒子被困在地球周围的辐射带中，距离在20,000-60,000公里之间，这是许多地球轨道卫星占据的空间的一部分。在高纬度，带电粒子可以从辐射带逃逸到高层大气中，在那里它们激发大气气体形成北极光(即“北极光”)。显然，这种日地连接不仅会带来美丽的自然现象，还会对我们所依赖的人造技术产生影响。据估计，宇宙中约99%的物质是等离子体。在这方面，太阳风、磁层和电离层并不稀奇。然而，等离子体并不自然地存在于地球表面。因此，如果我们想要充分了解等离子体(以及宇宙的大部分)是如何运行的，我们就需要开发环绕着我们星球的天然等离子体实验室。一些最大的谜团围绕着等离子体和电磁波的相互作用。例如，波-等离子体相互作用(WPI)被认为是导致冷等离子体被激发的许多过程的责任。这些包括地球辐射带的形成或等离子体的加速，这些等离子体导致极光并可能损坏卫星。然而，人们对这些机制知之甚少。在地面环境中，波-粒子相互作用经常被用作粒子加速器中的一种能量机制。由WPI加热的人工产生和限制的等离子体是实验聚变反应堆的核心，它为未来的清洁能源带来了希望。显然，更好地理解波-等离子体相互作用是至关重要的。概述了一个五年的研究计划。它的主要目标是解决这一普遍相关的物理过程。通过检查更接近地球的地区的WPI，那里的数据丰富，我们可以将结果外推到更广泛的太阳系和整个宇宙。该方案的组成部分通过以下方式处理与WPI有关的物理过程：(A)通过人为刺激WPI过程进行详细的积极实验，(B)在一定空间尺度上测量和分析自然WPI特征，(C)WPI过程的理论模型，以及(D)探索不同地球物理区域的WPI过程。

The Earth possesses a magnetic field very similar in shape to the magnetic field produced by a simple bar magnet. Magnetic field lines emerge from the planet at one magnetic pole and extend out of the atmosphere, thousands of kilometres into space, before returning to the magnetic pole in the opposite hemisphere. Rather than being a vacuum, the region of space that these field lines pass through is filled with plasma / an electrically conducting gas made up charged particles. Most of these particles originate in the Earth's atmosphere having been produced by ultraviolet sunlight which ionises gases in the high altitude atmosphere / a region known as the ionosphere. The Sun also possesses a strong magnetic field. As nuclear processes generate energy in the solar interior, the outer layer of the solar atmosphere expands outwards through the solar system forming the solar wind. When the solar wind arrives at the Earth it collides with the planet's magnetic field and is diverted around the planet. The cavity carved out of the solar wind by the Earth's magnetic field is called the magnetosphere. Inside the magnetosphere the plasma and magnetic field generally originate mainly from the Earth. Outside of the magnetosphere, they originate from the Sun. These regions are not always strictly separated and this leads to electromagnetic interactions between our planet and its nearest star. The ionosphere has a major influence on radio waves passing through it while some of the high energy particles that originate from the solar wind become trapped in radiation belts surrounding our planet at distances between 20,000-60,000 km / the part of space occupied by many Earth-orbiting satellites. At high latitudes, charged particles can escape from the radiation belts into precipitate into the upper atmosphere where they excite atmospheric gases to form the aurora borealis (i.e. the 'northern lights'). Clearly, this sun-earth connectivity not only leads to beautiful natural phenomena but also impacts upon the man-made technologies on which we depend. Approximately 99% of universe is estimated to be plasma. In this respect, the solar wind, the magnetosphere and the ionosphere are not exotic. However, plasma does not exist naturally on the surface of the Earth. Therefore, if we are to fully understand how plasma (and therefore most of the universe) behaves we need to exploit the natural plasma laboratory the surrounds our planet. Some of the biggest mysteries surround the interaction of plasmas and electromagnetic waves. For example, wave-plasma interactions (WPI) are thought to be responsible for many of the processes that cause cold plasma to be energised. These include the formation of the Earth's radiation belts or the acceleration of plasmas that cause the aurora and can damage satellites. However, the mechanisms are poorly understood. In a terrestrial setting, wave-particle interactions are frequently used as an energisation mechanism within particle accelerators. Artificially-created and confined plasmas heated by WPI lie at the heart of experimental fusion reactors that offer the hope of clean energy in the future. Clearly, an improved understanding of wave-plasma interactions is vitally important. A five-year programme of research is outlined. It's primary aim is to address this universally relevant physical process. By examining WPI in more accessible regions close to the Earth, where data are abundant, we can extrapolate results to the wider solar system and the universe as a whole. The components of the programme address the physical processes connected with WPI by means of: (a) detailed active experimentation by stimulating WPI processes artificially, (b) measurement and analysis of naturally WPI signatures at a range of spatial scales, (c) theoretical modelling of WPI processes, and (d) exploring WPI processes in different geophysical regions.