Ion Heating by Turbulence in the Solar Wind

太阳风是太阳喷射出的超音速等离子体。它充满了太阳系，并推动地球的磁层，造成地磁风暴。太阳风是非常多变的，它的速度从275公里/秒变化到更惊人的800公里/秒。在等离子体流中沿着的是太阳磁场。在大尺度上（数千个地球半径），等离子体和磁场一起移动，作为磁流体。这种磁流体是湍流的，速度和磁场的变化驱动着能量从这些大尺度到更小尺度的连续级联。湍流是一种混沌的随机过程，它改变了等离子体波动的特性。正是这些波动让宇宙射线和太阳耀斑粒子得以传播，并改变了其他太阳喷发物的方向和速度。太阳风是一个“天体物理实验室”;宇宙的绝大多数都充满了湍流等离子体，用航天器观测太阳风可以让我们深入了解整个宇宙的过程。湍流级联将能量从大尺度传输到较小尺度，并最终传输到如此小的尺度，使得等离子体不再表现得像流体。相反，我们必须考虑集体粒子动力学，它解释了等离子体的运动。在这一点上，磁场可以与粒子分布相互作用，并通过共振相互作用或随机“跳跃”直接加热它。现在有非常长和非常高质量的数据集，可用于研究等离子体湍流和新的任务即将启动，将提供无与伦比的观测来测试理论和发展关于太阳风动力学的新想法。这些数据可以用来研究大量与太阳风湍流有关的悬而未决的问题。在这个项目中，学生将使用来自Wind，ACE和Cluster任务的磁场和等离子体数据来研究湍流级联如何在小尺度上消散为热量。将使用小波技术测量与质子和阿尔法粒子相互作用的尺度上的磁螺旋度、相干性和波动的随机性，以便通过与质子和阿尔法粒子分布数据的相关性来确定太阳风中最普遍和最有效的加热机制（这些机制可能不相同）。同样的数据可以用来研究为什么太阳风中的α粒子比质子热？这项工作的最后结论将是一个量化的声明，什么是更重要的能量耗散在太阳风等离子体湍流：非线性随机加热或共振波粒子相互作用？

The solar wind is supersonic plasma ejected by the Sun. It fills the solar system and pushes against the Earth's magnetosphere causing geomagnetic storms. The solar wind is very variable, its speed changes from 275 km/s up to an even more staggering 800 km/s. Carried along in the plasma flow is the solar magnetic field. On large scales (many thousands of Earth radii) the plasma and magnetic field move together, acting as a magnetofluid. This magnetofluid is turbulent and the changes in velocity and magnetic field drive a continual cascade of energy from these large scales to smaller scales. The turbulence is a chaotic, stochastic process that alters the characteristics of the plasma fluctuations. It is these fluctuations through which cosmic rays and solar flare particles travel and that modify the direction and speed of other solar ejecta. The solar wind is an 'astrophysical laboratory'; the vast majority of the Universe is full of turbulent plasma and observing the solar wind with spacecraft can give us insight into the processes going on throughout the Universe. The turbulent cascade transports energy from the large scales to smaller scales and eventually to such small scales that the plasma no longer behaves like a fluid. Instead we must consider the collective particle dynamics that characterise kinetic motions of plasma. At this point the magnetic field can interact with the particle distribution and heat it directly, either through resonant interactions or through stochastic 'jumps'.There are now very long and very high quality data sets that can be used to study plasma turbulence and new missions launching soon that will provide unparalleled observations to test theories and develop new ideas about the dynamics of the solar wind. These data can be used to examine a large number of open questions relating to solar wind turbulence. In this project the student will use magnetic field and plasma data from the Wind, ACE and Cluster missions to investigate how the turbulent cascade dissipates into heat at small scales. Wavelet techniques will be used to measure the magnetic helicity, coherency and stochasticity of fluctuations that are at scales that interact with protons and alpha particles to determine through correlation with proton and alpha particle distribution data the most prevalent, and most effective heating mechanisms in the solar wind (these may not be the same). The same data can be used to investigate why alpha particles are hotter than protons in the solar wind? The final conclusion of the work will be a quantified statement about what is more important for energy dissipation in solar wind plasma turbulence: non-linear stochastic heating or resonant wave-particle interactions?