Coupled Kinetic Physics of Protons and Electrons in the Solar Wind

太阳风模拟问题具有重要的历史意义。相关研究仍在进行中，大多数模型依赖于太阳风的宏观（流体）模型。然而，当考虑波粒相互作用等动力学效应时，这种方法通常是不自洽的，因为某些类型的波浪湍流是预先假定的，并且波浪谱是建模的。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态和自一致的。这将极大地促进日球层物理学领域的知识。作为该项目的一部分，该模型将根据一系列参数预测太阳风等离子体存在的特定状态，允许观测到的数量与历史航天器数据以及帕克太阳探测器将获得的近太阳环境的计划测量进行测试。虽然目前的项目是一个理论项目，而不是一个涉及数据分析的项目，但由此产生的预测可能有助于实验学家更好地解释过去和未来的航天器数据。这有可能推动一个相关但不同的专业领域的知识，即实验太阳物理学。这个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太阳风膨胀中的大尺度动力学。要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使它们的温度接近各向同性——这是一种观测到的现象，但在理论上还没有得到令人满意的解释。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化的主要机制，但其不稳定性对于限制温度各向异性的上下限也很重要。本项目旨在通过放宽双麦克斯韦模型在不稳定性分析和碰撞输运计算中的假设来扩展前期工作。粒子和波的完整动力学方程，以及色散关系，将采用基于网格的数值格式求解。碰撞输运方程也将通过放宽双麦克斯韦模型的假设来求解。最后，通过求解宏观微观动力学方程，对非均匀性的影响进行了严格的研究。研究太阳风的理论模型对于理解和描述发生在日球层和整个宇宙的基本过程具有更广泛的意义。发现和了解近地环境和更广阔宇宙的基本物理过程，对人类未来的宇宙探索至关重要，也具有空间环境影响，因为现代文明越来越依赖于外层空间的电磁条件。建立太阳风的精确模型有助于实现这一更广泛的目标。从教育和培训的角度来看，本提案涉及一名年轻的博士后研究助理，这在更广泛的影响方面是一个主要优势。源源不断的年轻科学家接受STEM学科的教育和培训，对我们国家乃至整个人类社会健康的科学未来至关重要。PI过去一直致力于向美国和世界各地的年轻一代科学家教育和广泛传播他在职业生涯中获得的科学知识。因此，本建议将对年轻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。该奖项反映了美国国家科学基金会的法定使命，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.