Acceleration of Electrons in a Reconnecting Magnetotail

近地空间环境的动态是由太阳风和地球磁场之间的相互作用驱动的。地球黑暗面的一个特征是磁场中能量的循环储存和爆炸性释放。在这个过程中，磁能如何转化为加热和等离子体的大规模传输，我们仍然没有详细的了解。一个悬而未决的问题与电子加速到非常高的能量有关。观测表明，这种现象发生的规模比所涉及的小规模物理过程容易解释的范围要大得多。最近的研究证实，在这些事件期间，夜侧区域的大尺度动力学是能量的主要来源。为了全面、定量地描述高能电子的产生和演化，在广泛的尺度上纠缠复杂的混合过程是磁层物理学目前面临的一个重要挑战。该项目将利用先进的计算机代码的组合来模拟所涉及的小规模和大规模过程对颗粒的影响。航天器观察到的三个真实事件的模拟结果将被分析和比较，以确定电子在这些事件期间在哪里加速以及如何加速。该小组将采用新的多尺度方法，承诺对各种过程的相对作用提供第一次量化评估。它还将为跨尺度耦合的重要性提供至关重要的新见解。磁能转换过程是本研究的主题，是一种在广泛的空间和实验室等离子体中运行的通用等离子体物理过程。地球磁层是研究这种过程的天然实验室，在那里既可以进行模拟，也可以进行直接观测。因此，该项目的成果将影响广泛的研究领域。当能量很大的电子被推回地球时，它们可以影响近地空间环境。其中一些被困在那里更强的磁场中，对地球辐射带的构成做出了贡献。其他的则沉淀到高层大气中，在那里撞击有助于产生强烈的极光显示等。地球附近空间环境中的干扰效应令人关切，因为地球表面上的卫星和其他技术系统可能会受到影响。这为研究性研究增加了广泛的社会相关性和重要性。该项目将通过培养一名研究生来整合研究和教育。这位研究生将与团队成员一起工作，以补充他在多尺度过程中的论文工作。此外，一些本科生实习生将在暑期参与该项目。最后，PI是国际空间模拟学校(ISSS)计划委员会的创始人和成员。这所学校的重点是学生学习模拟技术。作为这一项目的一部分，国际和平协会将继续积极参与这项活动。这是一个以磁尾为中心的数值模拟项目。它的目标是确定电子在磁层亚暴期间在哪里以及如何加速。其目的是了解加速过程的多尺度性质，包括在中性线附近发生的动力学过程的影响，同时考虑到磁尾形状的全球变化。特别是，这项研究将量化重新连接和双极化锋面在亚暴事件期间为电子提供能量的相对作用。以前对与偶极化锋相关的电子的加速的研究是使用局部的格子粒子(PIC)模拟或基于从全球磁流体动力学(MHD)模拟获得的随时间变化的电场和磁场中跟踪大量电子的大规模动力学计算来进行的。在这里，将采用一种多尺度方法，纳入动力学过程的影响，包括在中性线附近发生的波粒相互作用，同时考虑到磁尾形状的全球变化。通过将边界处的磁场和粒子流设置为MHD结果给出的值，全局MHD模拟的结果将被用于确定三维粒子在单元中模拟的初始条件和边界条件。模拟系统将包括从重联地点发出的快速流出区域，该区域驱动双极化锋面的形成。在隐式粒子单元代码(IPIC3d)中看到的加速度将被表征，以解决重新连接位置附近的电子能量问题。最后，使用MHD模拟的电场和磁场进行的大规模动力学模拟将提供有关偶极前沿向地球移动时的能量和降水损失的信息。电子的绝热和非绝热加热的影响将在几个模拟中进行比较和对比，以确定不同亚暴的主要加速和加热机制是否不同，以及造成这种差异的原因。

The dynamics of the space environment near Earth is driven by the interaction between the solar wind and the Earth's magnetic field. A characteristic feature on the nightside of Earth is a cyclic storage and explosive release of energy in the magnetic field. The detailed understanding of how magnetic energy is converted into heating and large-scale transport of the plasma in this process still eludes us. One outstanding question concerns the acceleration of electrons to very high energies. Observations show that this happens on a much larger scale than can easily be explained by the small-scale physical processes involved. Recent studies have confirmed the large-scale dynamics of the nightside region during these events as the dominant source for the energization. Entangling the complex mix of processes over a wide range of scales for a comprehensive, quantitative description of the generation and evolution of the energetic electrons is an important current challenge in magnetospheric physics. This project will utilize a combination of advanced computer codes to simulate the effects on the particles of both the small- and large-scale processes involved. Simulation results from three real-life events observed by spacecraft will be analyzed and compared to determine where and how electrons are accelerated during these events. The novel multi-scale approach the team will employ promises to provide the first quantitative assessment of the relative roles of the various processes. It will also provide crucial new insights into the importance of cross-scale coupling. The magnetic energy conversion process that is the subject of this study is a generic plasma physics process that operates in a wide range of space and laboratory plasmas. The Earth's magnetosphere is a natural laboratory for studying such processes, where both simulations and direct observations are possible. Results from this project therefore will impact a broad variety of research areas. When the electrons with great energy are propelled back toward Earth, they can impact the near-Earth space environment. Some are trapped in the stronger magnetic field there and contribute to the make-up of the Earth radiation belts. Others precipitate into the upper atmosphere where the impact contributes to the creation, amongst others, of strong auroral displays. The disturbance effects in the space environment near Earth are of concern for satellites and other technological systems on the Earth surface that might be affected. This adds broad societal relevance and importance to the research study. The project will integrate research and education through the training of a graduate student. The graduate student will work with members of the team to complement his thesis work on multi-scale processes. In addition, a number of undergraduate interns will participate in the project during the summers. Finally, the PI is a founder and member of the program committee for the International School for Space Simulations (ISSS). This school focuses on student learning of simulation techniques. The PI will continue her active involvement with this activity as part of this project. This is a numerical modeling project focused on the magnetotail. Its goal is to determine where and how electrons are accelerated during magnetospheric substorms. The aim is to understand the multi-scale nature of the acceleration process by including the effects of kinetic processes that occur near the neutral line while taking into account the global changes in the configuration of the magnetotail. In particular, the study will quantify the relative role of reconnection and dipolarization fronts in energizing electrons during substorm events. Previous investigations of the acceleration of electrons associated with dipolarization fronts have been carried out using either local particle-in-cell (PIC) simulations or large-scale kinetic calculations based on following large numbers of electrons in the time dependent electric and magnetic fields obtained from global Magneto-Hydro-Dynamic (MHD) simulations. Here, a multi-scale approach will be adopted that incorporates the effects of kinetic processes, including wave-particle interactions that occur near the neutral line, while taking into account the global changes in the configuration of the magnetotail. The results of global MHD simulations will be used to determine the initial and boundary conditions of a three-dimensional particle in cell simulation by setting the magnetic fields and particle flows at the boundaries to the values given by the MHD results. The simulation system will include the region of fast outflow emanating from the reconnection site that drives the formation of dipolarization fronts. The acceleration seen in the implicit-particle-in-cell code (iPIC3d) will be characterized in order to address the questions of electron energization near the reconnection site. Finally, large-scale kinetic simulations using the electric and magnetic fields from the MHD simulation will provide information on energization and precipitation loss as the dipolarization front moves earthward. The effects of adiabatic and non-adiabatic heating of the electrons will be compared and contrasted between several simulations to determine whether the predominant acceleration and heating mechanisms are different for various substorms and what causes that variation.