AGS-PRF: A Continuum Kinetic Study of Heliospheric Collisionless Shocks

在太空和天体物理等离子体中，无碰撞激波无处不在，日光层也不例外。2013年国家研究委员会太阳和空间物理十年调查确定，无碰撞冲击是一种普遍的过程，有助于从超音速到亚音速流动的转变，加热等离子体，并加速高能粒子。行星弓激波提供了一种途径，将超音速和超阿尔文太阳风动能转化为其他形式的能量：等离子体热、粒子加速和电磁能量。尤其是地球的弓形激波一直是关于无碰撞激波给等离子体提供能量的方法的数据宝库，近年来由于磁层多尺度(MMS)任务而增加了研究热潮。在这个为期两年的博士后研究奖学金(PRF)项目中，PI将利用来自MMS的弓形激波交叉的现场数据来研究无碰撞激波。最近开发的诊断方法，例如场-粒子关联，当应用于来自MMS的分布函数数据时，将允许PI直接确认在磁鞘湍流中存在共振激励过程。他将在受到最近MMS弓激波交叉启发的模拟中部署场-粒子关联。PI将利用他开发的连续统Vlasov-Maxwell解算器来确定这些无碰撞激波中存在的能量过程，与传统的基于粒子的方法相比，该解算器提供了更高的分布函数保真度表示。研究工作将包括连续动力学模拟，这将提供前所未有的粒子分布函数的分辨率，从而能够仔细诊断无碰撞激波中存在的动力学过程。利用模拟的结果作为“Rosetta Stone”，PI将把场-粒子关联应用于相应的MMS数据，并完全表征这些弓激波交叉中的等离子体的能量。在项目期间，除了研究调查，PI将继续担任科学管家，利用他以前的外联和领导经验。他将为爱荷华大学的太空和科学鹰眼项目做志愿者，并参加该项目组织的公共外联活动。同样，他将与美国物理学会等离子体物理分部(APS DPP)的其他初级科学家合作，发展和开发针对学生和早期职业科学家的新项目，如学生日和论文演讲。尽管像MMS这样的太空任务提供了大量数据，并进行了补充的动力学模拟，但我们对无碰撞激波作为马赫数和激波几何形状(即激波法线和上游磁场之间的夹角)的演化的理解仍然不完整。激波上游由反射粒子发射的运动不稳定性和垂直激波平面内的波粒相互作用使能量传递显著复杂化。这个为期两年的PRF项目的主要目标是利用尖端技术对动力学方程进行数值积分，以及新的诊断方法，以阐明无碰撞冲击的能量转换机制。该项目解决了对日地研究计划至关重要的问题，例如“能量由太阳产生，传输到地球，并最终储存在陆地环境中的过程”。该PRF项目的研究和EPO议程支持AGS部门在发现、学习、多样性和跨学科研究方面的战略目标。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Collisionless shocks are ubiquitous in space and astrophysical plasmas, and the heliosphere is no exception. The 2013 National Research Council Decadal Survey for Solar and Space Physics identifies collisionless shocks as a universal process that facilitates the transition from supersonic to subsonic flow, heats the plasma, and accelerates energetic particles. Planetary bow shocks provide a route to converting the supersonic and super-Alfvenic solar wind bulk kinetic energy into other forms of energy: plasma heat, particle acceleration, and electromagnetic energy. The Earth’s bow shock in particular has been a treasure trove of data on the means by which collisionless shocks energize the plasma, with an increased flurry of study in recent years due to the Magnetospheric Multiscale (MMS) Mission. During this 2-year Postdoctoral Research Fellowship (PRF) project, the PI will utilize in-situ data of bow shock crossings from the MMS to study collisionless shocks. Recently developed diagnostics, such as the field-particle correlation, when applied to the distribution function data from MMS, will allow the PI to confirm directly the presence of resonant energization processes in magnetosheath turbulence. He will deploy the field-particle correlation on simulations inspired by recent MMS bow-shock crossings. The PI will determine the energization processes present in these collisionless shocks by utilizing the continuum Vlasov-Maxwell solver developed by him, which provides a much higher fidelity representation of the distribution function compared to traditional particle-based methods. The research work will comprise continuum kinetic simulations, which would provide unprecedented resolution of the particle distribution function, thus allowing careful diagnosis of the kinetic processes present in the collisionless shocks. Using the results of the simulations as a “Rosetta Stone,” the PI will apply the field-particle correlation to the corresponding MMS data, and completely characterize the energetics of the plasma in these bow-shock crossings. During the project, alongside the research investigations, the PI will continue to serve as a steward of science, using his previous outreach and leadership experience. He will volunteer for the Hawkeyes in Space and Science programs at the University of Iowa and participate in the public outreach events organized by the programs. Likewise, he will work with fellow junior scientists in the American Physical Society’s Division of Plasma Physics (APS DPP) to grow and develop new programs aimed at students and early career scientists, such as the Student Day and Dissertation Talks. Despite the large volume of data coming out of space missions like the MMS, and complementary kinetic simulations, our understanding of the evolution of a collisionless shock as a function of Mach number and shock geometry, i.e., the angle between the shock normal and upstream magnetic field, remains incomplete. Kinetic instabilities upstream of the shock launched by reflected particles and wave-particle interactions in the plane perpendicular to the shock significantly complicate the energy transfer. The primary aim of this 2-year PRF project is to leverage cutting edge techniques for numerically integrating the kinetic equation, as well as novel diagnostics, to illuminate the energy conversion mechanisms of a collisionless shock. The project addresses questions of fundamental importance to the Solar-Terrestrial Research program, such as “processes by which energy is generated by the Sun, transported to the Earth, and ultimately deposited in the terrestrial environment.” The research and EPO agenda of this PRF project supports the Strategic Goals of the AGS Division in discovery, learning, diversity, and interdisciplinary research.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.