Dissipation and particle acceleration in collisionless shock waves

地球磁场对太阳风形成障碍，在地球周围产生一个动态空洞，称为磁层。当太阳风在磁层上方流动的速度快于局部波速时，激波就会在磁层前面形成，其方式类似于子弹或超音速喷气式飞机形成的音爆。太空中的冲击波也可以在超新星、日冕物质抛射和恒星周围观察到。在太空中，冲击波不能通过粒子碰撞来耗散能量，因为密度太低了。相反，必须对粒子尺度的电磁等离子体过程负责。然而，导致激波加热和加速的不同现象之间的平衡还没有完全被了解。最近的航天器观测和模拟表明，在一些激波的过渡层内可以发生湍流和磁重联。然而，我们还不知道这些过程对更广泛系统中的等离子体加热有多重要，也不知道它们是否有助于高能宇宙射线的产生。在这个项目中，学生将使用来自NASA的磁层多尺度和帕克太阳探测器等航天器的现场卫星数据，以及高性能的并行等离子体模拟。通过比较观测和计算方法获得的数据，他们将识别不寻常的等离子体结构，并描述嵌入激波内部的湍流过渡区。学生将有机会定期与国际团队接触，并为我们理解冲击波如何在太空中重新分配能量做出重大贡献。

Earth's magnetic field forms an obstacle to the solar wind, generating a dynamic cavity around Earth known as the magnetosphere. As the solar wind flows over the magnetosphere faster than the local wave speed, a shock wave forms ahead of the magnetosphere in similar fashion to the sonic boom formed by a bullet or supersonic jet. Shock waves in space are also observed around supernovae, coronal mass ejections, and stars. In space, shock waves cannot dissipate energy with particle collisions, because the density is much too low. Instead, particle-scale electromagnetic plasma processes must be responsible. However, the balance of different phenomena that can contribute to heating and acceleration by shock waves is not yet fully understood.Recent spacecraft observations and simulations have shown that turbulence and magnetic reconnection can occur within the transition layer of some shock waves. However, we do not yet know how significant these processes are to plasma heating in the broader system, or if they can contribute to the generation of high energy cosmic rays.During this project, the student will use both in situ satellite data from spacecraft such as NASA's Magnetospheric Multiscale and Parker Solar Probe, and high-performance, parallelised plasma simulations. Using comparisons of data obtained by observational and computational methods, they will identify unusual plasma structures and characterise the turbulent transition region embedded inside shock waves. The student will have the opportunity to regularly engage with international teams and make significant contributions to our understanding of how shock waves repartition energy in space.