Electron Distribution in the Solar Wind from the Sun to the Earth

太阳风是一股热电离气体或等离子体流，从日冕扩散到行星际介质中。自 1959 年发现太阳风以来，太空科学家一直在研究太阳风中质子和电子的行为、它们与遍布星际空间的磁场以及行星磁层的相互作用。大约在同一时间，等离子体物理学家正在考虑容纳比日冕中的等离子体热一百倍的等离子体，以获得受控聚变反应——一种几乎取之不尽的相对清洁和安全的能源。他们想出了所谓的镜子机器，一种类似于瓶子的磁性结构，两端有两个开口。然而，这样的设备并不理想——热等离子体可能会通过瓶颈开口泄漏并从密闭室流出。 该项目将逃离镜子机器的等离子体与从热日冕中膨胀的等离子体进行类比。它将利用等离子体聚变研究中开发的理论框架来解释太阳风中电子的行为，这是空间等离子体物理学的基本问题之一。 该项目研究从热日冕膨胀的太阳风等离子体。它解决了以下问题：给定日冕附近的电子分布函数，在较大的日光层距离处所得的分布函数是什么？该项目与等离子镜机建立了类比。与镜面机扩展器类似，太阳风电子分布函数包含沿磁场线流动的电子束和准各向同性核心，一方面与从光束散射的电子相关，另一方面为流动的电子提供散射。该项目开发了一个新的自洽理论框架来解决这个问题。研究的结果将是电子分布作为径向距离的函数。这将使人们能够特别了解背景等离子体中的径向能量转移和能量沉积、膨胀区域中的等离子体温度分布、电子不稳定性以及由此产生的等离子体湍流。结果将与现有观测结果进行比较，特别是对于帕克太阳探测器数据的解释可能很有价值。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力优点和更广泛的影响审查标准进行评估，被认为值得支持。

The solar wind is a stream of hot ionized gas, or plasma, expanding from the solar corona into the interplanetary medium. Since its discovery in 1959, space scientists have been studying the behavior of protons and electrons in the solar wind, their interaction with the magnetic fields pervading interstellar space, and with magnetospheres of planets. At approximately the same time, plasma physicists were thinking about containing plasma that is a hundred times hotter than that in the solar corona, to obtain controlled fusion reaction – a virtually inexhaustible source of relatively clean and safe energy. They came up with the so-called mirror machine, a magnetic configuration resembling a bottle with two openings at the opposite ends. However, such a device was not ideal – hot plasma could leak through the bottleneck openings and stream away from the confinement chamber. This project establishes the analogy between the plasma escaping the mirror machine and the plasma expanding from the hot solar corona. It will use the theoretical framework developed in plasma fusion studies to explain the behavior of electrons in the solar wind, one of the fundamental problems of space plasma physics. The project studies the solar wind plasma expanding from the hot solar corona. It addresses the following question: given the electron distribution function near the solar corona, what is the resulting distribution function at larger heliospheric distances? The project establishes the analogy with the plasma mirror machines. Similarly to the mirror-machine expander, the solar wind electron distribution function contains a beam of electrons streaming along the magnetic field lines and a quasi-isotropic core that, on one hand, is related to the electrons scattered from the beam and on the other, provides scattering for the streaming electrons. The project develops a new self-consistent theoretical framework for solving this problem. The outcome of the study will be the electron distribution as a function of radial distance. This will allow one to understand, in particular, the radial energy transfer and energy deposition in the background plasma, the plasma temperature profile in the expansion region, the electron instabilities and the resulting plasma turbulence. The results will be compared with available observations, and in particular, may be valuable for the interpretation of the Parker Solar Probe data.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.