GEM: Energy Conversion Associated with Non-equilibrium Velocity Distribution Functions in Dayside Magnetopause Reconnection

昼侧磁层顶重联控制等离子体和能量从太阳风输入到磁层。它与显著的等离子体加热和粒子加速有关，但这些过程尚未得到很好的理解。一个原因是功、内能和热之间的能量转换传统上被定义为麦克斯韦分布，并且用速度分布函数（VDF）的低阶矩来测量，但是在无碰撞等离子体中，VDF经常出现在非麦克斯韦状态。这样的非平衡分布可能是不稳定的，从而产生不稳定性和等离子体波，这些不稳定性和等离子体波通过自洽的波粒相互作用影响VDF。该项目研究与非平衡VDFs相关的能量转换，这是了解和预测空间天气的一项重要研究。这项工作支持早期职业PI和来自STEM代表性不足的群体的博士后。本科生将通过每年的马里兰州日活动进行辅导和推广。该项目的目的是了解何时，何地，如何和多少，与非平衡VDFs相关的能量转换发生在昼侧磁层顶重联。科学问题：（1）在2.5维（2.5D）非对称磁场重联的不同区域中，与非平衡VDFs相关的能量转换（用动能熵测量）发生在何时何地，它们对能量转换的机制有何启示？(2)在2.5维非对称磁场重联中，在不同的导场强度和反磁漂移速度条件下，能量转换过程有什么不同？(3)2.5D和3D非对称重联之间能量转换过程有什么不同？方法学：使用粒子模拟，该团队将分析（1）波活动的存在，（2）VDFs是否朝向或远离Maxwellianity演化，以及（3）混沌运动的存在。通过比较这些结果，他们将发现高阶矩参与能量转换的位置，并解开波是激发粒子还是非麦克斯韦VDF产生波。利用非麦克斯韦性的时间演化来理解波粒相互作用是一种全新的技术。结果将与磁层多尺度观测结果进行比较。该项目与全球太阳物理学基金会焦点小组“太阳物理学系统观测时代的磁重联”直接相关。该奖项反映了NSF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。

Dayside magnetopause reconnection controls plasma and energy input into the magnetosphere from the solar wind. It is associated with significant plasma heating and particle acceleration, yet these processes are not well-understood. One reason is that energy conversion between work, internal energy, and heat is traditionally defined for Maxwellian distributions and measured with lower order moments of the velocity distribution function (VDF), but in collisionless plasmas, the VDFs frequently appear in a non-Maxwellian state. Such non-equilibrium distributions can be unstable to the generation of instabilities and plasma waves which affect the VDFs via self-consistent wave-particle interactions. This project investigates energy conversion associated with non-equilibrium VDFs, an important study for understanding and predicting space weather. The work supports an early career PI and a post-doc from an under-represented group in STEM. Undergraduate students will be mentored and outreach conducted through the annual Maryland Day event.This project aims to understand when and where, and how and how much, the energy conversion associated with non-equilibrium VDFs occurs during dayside magnetopause reconnection. Scientific questions: (1) When and where does energy conversion associated with non-equilibrium VDFs, as measured by the kinetic entropy, occur in different regions of 2.5-dimensional (2.5D) asymmetric magnetic reconnection, and what do they imply about the mechanisms of energy conversion? (2) What are the differences of energy conversion processes occurring for different conditions of guide field strengths and diamagnetic drift speeds in 2.5D asymmetric magnetic reconnection? (3) What are the differences of energy conversion processes occurring between 2.5D and 3D asymmetric reconnection? Methodology: Using particle-in-cell simulations, the team will analyze (1) the presence of wave activity, (2) whether VDFs evolve towards or away from Maxwellianity, and (3) the presence of chaotic motions. By comparing these results, they will find where higher order moments are participating in energy conversion and disentangle whether the waves are energizing particles or non-Maxwellian VDFs are generating waves. Using the time evolution of non-Maxwellianity to understand wave-particle interactions is a brand-new technique. The results will be compared to Magnetospheric Multiscale (MMS) observations. This project is directly relevant to the GEM Focus Group, “Magnetic Reconnection in the Age of the Heliophysics System Observatory”.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.