Multiscale Phenomena in Plasmas from Collisional to Collisionless Regimes

该项目旨在建立一个等离子体（带电粒子气体）的数值模型，该模型将结合小尺度等离子体过程的非常详细的描述和大尺度等离子体过程的粗略描述。科学理解是通过精确描述自然现象的数学模型的发展和应用而进步的。最高保真度的模型提供了最准确的描述，但往往难以解决。简化的模型更容易解决，但可能无法捕获指示系统演变的相关交互。该项目旨在开发一种混合模型，将高保真度和低保真度的描述结合在一起。低保真度组件应用于模型在形式上有效的所有领域，高保真度组件仅应用于绝对需要的领域。混合模型将用于研究磁化流动等离子体的演化，类似于太阳等离子体与地球磁层相互作用的情况。了解这些相互作用可以预测空间尺度之间的能量转移，最终影响GPS和通信卫星。本项目旨在探索等离子体中的多尺度现象和研究磁化开尔文-亥姆霍兹不稳定性（KHI）的新方法。等离子体固有地表现出多尺度物理，这源于组成物质的电子和离子质量的巨大差异，以及电磁场和碰撞产生的远距离和短程相互作用。然而，在模拟中捕捉尺度的大分离仍然是一个突出的挑战。碰撞性表达了远距离和短程相互作用的相对重要性，并在确定尺度的扩展和耦合方面发挥重要作用。在高碰撞状态下准确的模型在无碰撞状态下失败，而在无碰撞状态下准确的模型在碰撞状态下计算上是禁止的。利用多流体模型的计算效率和动力学模型的高保真度，将开发一种混合方法，通过区域分解将模型耦合以探索多尺度现象。流体和动力学模型的连续体表示将通过组成等离子体种的概率分布函数的矩促进耦合。磁化后的KHI可以形成宏观等离子体结构，其细节取决于微观物理。混合模型将被应用于磁化KHI的研究，以深入了解最终驱动输运和决定能量分配的多个尺度之间的相互作用。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。

This project seeks to develop a numerical model of a plasma - a gas of electrically charged particles - that will combine a very detailed description of plasma processes on small scales with a coarser description of large scales. Scientific understanding is advanced through the development and application of mathematical models that accurately describe natural phenomena. The highest fidelity models provide the most accurate description but are often too difficult to solve. Simplified models are easier to solve but can fail to capture the relevant interactions that dictate a system’s evolution. This project seeks to develop a hybrid model that stitches together high-fidelity and low-fidelity descriptions. The low-fidelity component is applied to all domains where the model is formally valid, and the high-fidelity component is applied only where it is absolutely required. The hybrid model will be applied to study the evolution of magnetized flowing plasmas, similar to the situation that occurs as plasma flowing from the Sun interacts with Earth's magnetosphere. Understanding these interactions can provide predictions about energy transfer between spatial scales that can ultimately impact GPS and communication satellites.This project aims to develop a new approach to explore multiscale phenomena in plasmas and to investigate the magnetized Kelvin-Helmholtz instability (KHI). Plasmas inherently exhibit multiscale physics that originate from the large differences in electron and ion masses of the constituent species and from the long-range and short-range interactions that are produced by electromagnetic fields and collisions. However, capturing the large separation of scales in simulations remains an outstanding challenge. Collisionality expresses the relative importance of long-range and short-range interactions and can play an important role in determining the spread and coupling of scales. Models that are accurate in the highly collisional regime fail in the collisionless regime, while models that are accurate in the collisionless regime are computationally prohibitive in the collisional regime. Exploiting the computational efficiency of multi-fluid models and the high-fidelity of kinetic models, a hybrid approach will be developed to couple the models through domain decomposition to explore multiscale phenomena. Continuum representations for the fluid and kinetic models will facilitate coupling through moments of the probability distribution functions of the constituent plasma species. The magnetized KHI is known to develop macroscale plasma structures whose details depend on microscale physics. The hybrid model will be applied to study the magnetized KHI to gain insight into the interplay between the multiple scales that ultimately drive transport and dictate the partition of energy.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.