Suprathermal Energization of Particles in the Vicinity of Cusp-like Field Configurations

该项目将利用航天器观测、数值模拟和实验室实验来研究太阳风等离子体——从太阳表面吹出的电子和离子——如何与地球磁层相互作用。空间中充满了由大约等量的带负电荷的电子和带正电荷的离子组成的等离子体。离我们最近的恒星，太阳，向地球喷射出大量快速移动的等离子体，称为太阳风。这种等离子体相对较冷，但当它遇到磁化的行星时，会迅速加热。地球的磁场在一定程度上保护了我们免受太阳风的影响，但这种屏蔽也会通过一种叫做磁重联的机制被破坏。目前还不太清楚为什么地球磁屏蔽内的等离子体，即磁层，与太阳风相比如此热，而这个奖项将使安柏瑞德航空大学和威斯康星大学麦迪逊分校的合作团队能够帮助解决这个问题。该项目还将有助于我们对太空天气的理解，并教育、指导和支持两名博士生和三名来自代表性不足群体的科学家。等离子体中粒子加速、加热和输运的普遍性仍然是等离子体物理学、空间物理学和天体物理学面临的主要挑战。在实验室等离子体中，与空间等离子体的物理过程相比，长度尺度更短，时间尺度更快，这使得测量和确定具体的物理机制成为一项挑战。在空间中，原位测量探测等离子体的自然尺度，但探针的空间分布非常稀疏。最近的多航天器观测和数值模拟揭示了地球日侧磁层大规模磁瓶结构（抗磁腔）的产生机制，在那里数十eV的热粒子可以被加速到大于40 keV的超热能量。然而，粒子加速的详细物理原理仍然难以捉摸。该项目将回答以下科学问题：(1)在抗磁腔（DMC）环境中通过重连接（例如，电子加速器与费米）使电子能量的详细物理原理是什么？(2)高伦德奎斯特数等离子体中dmc形成的时间尺度是什么？(3)在高伦德奎斯特数实验室等离子体中，DMC中的电子等离子体性质如何随着外部电子参数的变化而变化？与偶极子场周围的通量相比，是什么控制了重连接通量的比例？该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This project will use spacecraft observations, numerical simulations and laboratory experiments to study how solar wind plasma -- the electrons and ions blowing off the surface of the Sun -- interact with the magnetosphere of the Earth. Space is filled with plasma consisting of approximately equal amounts of negatively charged electrons and positively charged ions. Our nearest star, the Sun, ejects large quantities of fast-moving plasma, called the solar wind, toward the Earth. This plasma is relatively cold but is rapidly heated when it encounters magnetized planets. The Earth’s magnetic field partly shields us from the solar wind, but this shield can also break via a mechanism called magnetic reconnection. It is not well understood why the plasma inside the Earth’s magnetic shield, the magnetosphere, is so hot when compared to the solar wind, and this award will enable a collaborative team from Embry-Riddle Aeronautical University and the University of Wisconsin - Madison to help address this question. The project will also contribute to our understanding of space weather and educate, mentor, and support two Ph.D students as well as three scientists from under-represented groups. The universality of particle acceleration, heating and transport in plasmas remains a major challenge in plasma physics, space physics, and astrophysics. In laboratory plasmas, the length-scales are shorter and time-scales are faster than for physical processes in space plasmas, making it a challenge to measure and identify the specific physical mechanisms responsible. In space, the in-situ measurements probe plasmas at their natural scales, but the spatial distribution of probes is very sparse. Recent multi-spacecraft observations and numerical simulations have revealed generation mechanisms of large-scale magnetic bottle structures (diamagnetic cavities) at the Earth’s dayside magnetosphere where thermal particles of tens of eV can be accelerated to suprathermal energies of greater than 40 keV. However, the detailed physics of the particle acceleration has remained elusive. This project will answer the following science questions: (1) What is the detailed physics for electron energization by reconnection (e.g., betatron vs. Fermi) in the environment of a diamagnetic cavity (DMC)?; (2) What is the time-scale of formation of the DMCs in high-Lundquist number plasmas?; (3) How do the electron plasma properties change in the DMC with respect to external electron parameters in high-Lundquist number laboratory plasmas and what controls the fraction of reconnected flux compared to flux convected around the dipole field?This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.