Kinetic and Multiscale Simulations of Particle Acceleration in Astrophysical Shocks

这个项目将研究粒子如何在天体物理源中被加速到高速，重点是一种被称为费米加速的特殊机制。尽管人们相信，在脉冲星、超新星和其他强源周围流动的物质中，相当大一部分能量可以转化为非常快的粒子，这些粒子可以通过它们发出的辐射模式来识别，但其机制尚不清楚。在这项研究之后，费米机制将得到更好的描述，并可能受到严格的约束。粒子在无碰撞激波中的加速是宇宙中大多数非热现象模型的核心。对同步辐射的观测表明，脉冲星风星云、活动星系核喷流、伽马射线爆发和超新星遗迹中的这种冲击，可以将相当大一部分流动能量转化为具有幂定律光谱的相对论粒子。然而，虽然它通常被引用为原因，但一阶费米机制的运行条件及其效率并没有从第一原理中得到理解。该项目将通过对天体物理无碰撞冲击进行大规模多维粒子模拟和混合模拟来构建冲击加速的自洽理论，并研究等离子体不稳定性、粒子散射和磁场产生的微观物理，这是校准非线性扩散冲击加速理论所必需的。具体问题包括：1)激波加速的存在标准及其效率；2)加速粒子如何影响激波结构和演化；3)在现实激波中产生的质子和电子能谱。在这项工作中开发的工具将能够对激波进行多尺度模拟，并将从第一性原理得出非线性区域的粒子谱。这项研究将为无碰撞激波中的费米加速是高能宇宙射线和非热粒子的起源的假设提供预测能力，并可能对磁化模型和天体物理外流的组成施加严格的约束。由于费米加速是天体物理学中的一个基本过程，因此其结果将对研究高能天体物理和宇宙源的观察者、实验者和理论家有价值，甚至适用于太阳系的冲击。这一发现将指导新一代实验室实验。这项工作将涉及博士后、研究生和本科生，对他们进行数值建模和可视化方面的培训，从而为他们在科学和技术领域的职业生涯做好准备，在科学和技术领域，大规模计算日益发挥着重要作用。将开发一种交互式等离子体物理教程，以使专家和普通公众对这些棘手的主题有直观的了解。

This project will study how particles get accelerated to high speeds in astrophysical sources, focusing on a special mechanism known as Fermi acceleration. Although it is believed that a considerable fraction of the energy in material flowing around pulsars, supernovae, and other strong sources, can be converted into very fast particles, which are identified by the patterns of radiation they give off, the mechanism is not well understood. After this study, the Fermi mechanism will be much better characterized, and may be tightly constrained.Acceleration of particles in collisionless shocks is at the heart of most models of non-thermal phenomena in the Universe. Observations of synchrotron emission suggest that such shocks in pulsar wind nebulae, in jets from active galactic nuclei, in gamma-ray bursts, and in supernova remnants, can convert a significant fraction of the flow energy into relativistic particles with power-law spectra. However, although it is usually invoked as the cause, the conditions for operation of the first-order Fermi mechanism and its efficiency are not understood from first principles. This project will construct a self-consistent theory of shock acceleration by performing large-scale multidimensional particle-in-cell and hybrid simulations of astrophysical collisionless shocks, and study the microphysics of plasma instabilities, particle scattering, and magnetic field generation, necessary to calibrate nonlinear diffusive shock acceleration theory. Specific questions include: 1) the criteria for existence of shock acceleration, and its efficiency; 2) how accelerated particles influence shock structure and evolution; 3) the proton and electron spectra generated in realistic shocks. The tools developed during this work will enable multi-scale modeling of shocks and will derive particle spectra in the nonlinear regime from first principles. This research will provide predictive power to the hypothesis that Fermi acceleration in collisionless shocks is the origin of high-energy cosmic rays and non-thermal particles, and could place tight constraints on the models of magnetization and on the composition of astrophysical outflows.Because Fermi acceleration is a fundamental process in astrophysics, the results will be of value to observers, experimentalists, and theorists studying high-energy astrophysical and cosmological sources, and are even applicable to shocks in the solar system. The findings will guide a new generation of laboratory experiments. The work will involve postdocs, and graduate and undergraduate students, training them in numerical modeling and visualization, and thus preparing them for careers in science and technology fields, where large-scale computing increasingly plays an important role. An interactive plasma physics tutorial will be developed to bring intuitive understanding of these thorny subjects to specialists and the general public alike.