Coupled Kinetic Physics of Protons and Electrons in the Solar Wind

太阳风的模拟问题一直具有重要的历史意义。 相关的研究正在进行中，大多数模型依赖于太阳风的宏观（流体）模型。 然而，当考虑动力学效应（如波粒相互作用）时，该方法通常不自洽，因为假定了某些类型的波湍流，并对波谱进行了建模。 相比之下，作为这个为期三年的项目的一部分，将开发的理论模型将是完全动力学和自洽的。 这将大大推进日光层物理学领域的知识。 作为该项目的一部分而开发的模型将预测太阳风等离子体存在的特定状态，并给出一套参数，从而可以对照历史航天器数据以及计划由帕克太阳探测器获得的近太阳环境测量数据来检验观测到的数量。 尽管目前的项目是一个理论项目，而不是涉及数据分析的项目，但由此产生的预测可能会帮助实验者更好地解释过去和未来的航天器数据。 这项为期三年的研究项目将从理论上研究电子和离子（质子）通过碰撞和不稳定过程的动力学耦合如何影响膨胀的太阳风中的大尺度动力学。 有待研究的具体问题涉及到动态耦合的太阳风电子和质子如何促成其温度的近各向同性-这是一种尚未得到令人满意的理论解释的观察到的现象。 PI基于双麦克斯韦粒子分布假设的初步工作表明，碰撞过程可能是温度各向同性的主要机制，但不稳定性对于限制温度各向异性的上/下限也很重要。本计画的目的是在不稳定性分析与碰撞输运计算中，放宽双麦克斯韦模型的假设，以扩充前期的工作。 粒子和波的完整动力学方程以及色散关系将通过基于网格的数值方案求解。 碰撞输运方程也将通过放松双麦克斯韦模型的假设来求解。 最后，将通过求解宏观-微观动力学方程来严格研究不均匀性的影响。从更广泛的角度来理解和描述日光层和整个宇宙中发生的基本过程，对太阳风理论建模的研究是重要的。 发现和了解近地环境和更广阔宇宙中的基本物理过程，对于人类今后探索宇宙至关重要，而且也会对空间环境产生影响，因为现代文明越来越依赖外层空间的电磁条件。 开发一个精确的太阳风模型有助于实现这样一个更广泛的目标。从教育和培训的角度来看，目前的建议涉及一名年轻的博士后研究助理，这是更广泛影响方面的一个主要优势。 对于我们国家和整个人类社会的健康科学未来来说，重要的是要有源源不断的年轻科学家接受STEM学科的教育和培训。 PI在过去一直致力于教育和广泛传播他的职业生涯中获得的科学知识，以年轻一代的科学家都来自美国和世界各地。 因此，本提案将对青年科学家的教育和培训产生更广泛的影响。 该项目的研究和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。

The problem of solar wind modeling has been of historical significance. The related research is ongoing, and most models rely on macroscopic (fluid) models of the solar wind. When kinetic effects, such as wave-particle interaction, are considered, however, the approach is usually not self-consistent in that certain types of wave turbulence is presupposed, and the wave spectra are modeled. In contrast, the theoretical model to be developed as part of this three-year project will be fully kinetic and self-consistent. This will significantly advance the knowledge in the field of heliospheric physics. The model to be developed as part of this project will predict a particular state in which the solar wind plasma exists given a set of parameters, allowing the observed quantities to be tested against historic spacecraft data as well the planned measurements of the near-Sun environment that will be obtained by the Parker Solar Probe. Although the present project is a theoretical one, rather than one involving data analysis, the resulting prediction may help experimentalists better interpret the past and future spacecraft data. This has the potential to advance knowledge in a related, but different field of expertise, namely experimental heliophysics.This three-year research project will investigate theoretically how the kinetic coupling of electrons and ions (protons) via collisional and instability processes affect the large-scale dynamics in the expanding solar wind. The specific problem to be investigated relates to how the dynamically coupled solar wind electrons and protons contribute to the near isotropization of their temperatures -- an observed phenomena which has not yet been satisfactorily explained theoretically. The PI's preliminary work based upon the assumption of bi-Maxwellian particle distribution shows that collisional process may be the dominant mechanism for the isotropization of temperatures, but the instabilities are important too for limiting the upper/lower bounds of temperature anisotropies. This project aims to extend the preliminary work by relaxing the assumption of bi-Maxwellian model in both instability analysis and collisional transport calculation. The full kinetic equations for particles and waves, as well as the dispersion relation, will be solved by grid-based numerical scheme. The collisional transport equation will also be solved by relaxing the assumption of bi-Maxwellian models. Finally, the effects of inhomogeneities will be rigorously investigated by solving the macro-microscopic kinetic equation.The research on the theoretical modeling of the solar wind is important from the broader perspective of understanding and characterizing fundamental processes that take place within the heliosphere and throughout the universe. Discovering and understanding the basic physical processes in the immediate near-Earth environment and in the wider universe is essential for future human explorations of the universe, and it also has a space environmental impact, as the modern civilization is increasingly dependent on electromagnetic conditions in outer space. Developing an accurate model of the solar wind contributes to such a wider goal. From the perspective of education and training, the present proposal involves a young post-doctoral research associate, which is a major strength in terms of Broader Impacts. It is important for the healthy scientific future of our nation -- and the entire human society -- that a steady stream of young scientists are educated and trained in STEM disciplines. The PI has in the past always strived to educate and widely disseminate the scientific knowledge acquired during his career to younger generation of scientists both from the U.S. and worldwide. The present proposal will thus have a broader impact on the education and training of a young scientist. The research and EPO agenda of this 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.