NSF-BSF: Collaborative Research: Rankine-Hugoniot Conditions Relating the Gyrotropic Regions of Collisionless Shocks in Non-Thermal Plasma

该项目将在空间和实验室环境中开发一种新的、更精确的稀薄等离子体冲击波模型。所谓的无碰撞激波属于发生在热等离子体和稀薄等离子体中的最基本现象。天体物理波加速粒子，耗散能量，并通过将等离子体流的动态压力转化为热能，强烈扰乱它们传播的环境。现代等离子体物理学的核心理论问题之一是对冲击波（下游）后等离子体状态的定量预测，其前面是给定参数（上游）。大多数直接观测到的无碰撞冲击发生在日球层；然而，它们也可以在实验室中创造出来。这个项目的巨大挑战是发展一种新的理论方法，一方面，解释单个粒子如何在无碰撞等离子体中与激波相互作用的细节，但另一方面，确定上游和下游条件之间易于使用的关系，类似于空气动力学中广泛用于激波的关系。该项目将培养计算科学和等离子体物理学方面的学生和博士后，并通过与美国-以色列两国科学基金会支持的本古里安大学合作，使他们接触国际科学合作。无碰撞冲击（CSs）在许多空间物理学、天体物理学和实验室环境中是普遍存在的。尽管经过了60多年的CS研究，但与早期的进展相比，该问题的现状基本没有变化。标准的Rankine-Hugoniot条件在CSs中的应用要么是无效的，要么是非常不准确的。本研究的目的是将激波前沿的基本离子动力学纳入统计描述，这将使其成为可能，一方面，避免进入离子运动的细节，另一方面，放弃与状态方程相关的临时假设。局部混合和全动力学PIC模拟将用于验证和改进概率、测试粒子方法。本研究将通过提供一种可以与实际观测进行定量比较的理论，确保CS物理学向前迈出实质性的一步。概率方法预计对等离子体物理的其他问题是有效的，在这些问题中，目前不可能有完全的动力学方法，而基于流体近似的假设是无效的。它的相对简单性和覆盖范围广泛的冲击参数的能力使得创建方便的分析公式和/或查找表成为可能，供广泛的等离子体物理学家使用。这也将有助于发展涉及无碰撞冲击的全球磁流体动力学模型，特别是能够更准确地预测空间天气。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 will develop a new and more accurate model of shock waves in rarefied plasmas in space and laboratory environments. So-called collisionless shock waves belong to the most fundamental phenomena occurring in hot and rarified plasmas. Astrophysical waves accelerate particles, dissipate energy, and strongly perturb the environment they propagate through by converting dynamic pressure of a plasma flow into thermal energy. One of the central theoretical issues in modern plasma physics is a quantitative prediction of the plasma state behind a shock wave (downstream) for given parameters in front of it (upstream). The majority of directly observed collisionless shocks are in the heliosphere; however, they can also be created in a laboratory. The grand challenge of this project is to develop a new theoretical approach that would, on the one hand, account for the details of how individual particles interact with shock waves in collisionless plasma, but on the other hand, identify easy-to-use relationships between upstream and downstream conditions, similar to those widely used for shock waves in aerodynamics. The project will train students and postdocs in computational science and plasma physics, as well as expose them to international science cooperation via collaboration with Ben Gurion University supported by the U.S. - Israel Binational Science Foundation.Collisionless shocks (CSs) are ubiquitous in many space physics, astrophysics, and laboratory settings. Despite more than six decades of CS research, the present status of the problem remains essentially unchanged in comparison to the early advances. Application of standard Rankine–Hugoniot conditions to CSs is either invalid or highly inaccurate. The objective of this research is to incorporate the essential ion dynamics at shock fronts into a statistical description which would make it possible, on the one hand, to avoid going into details of ion motion and, on the other hand, abandon ad hoc assumptions related to the equations of state. Local hybrid and fully-kinetic PIC simulations will be used to validate and improve on the probabilistic, test-particle approach. This research will ensure a substantial step forward in the CS physics by providing a theory which can be compared quantitatively with real observations. The probabilistic approach is expected to be efficient for other problems of plasma physics, where the full kinetic approach is currently impossible, while the assumptions based on the fluid approximation are not valid. Its relative simplicity and ability to cover a wide range of shock parameters makes it possible to create convenient analytic formulae and/or lookup tables to be used by a wide range of plasma physicists. These will also be useful for the development of global magnetohydrodynamic models involving collisionless shocks enabling, in particular, more accurate forecasting of space weather.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.