Particle Acceleration in Astrophysical Collisionless Shocks

AST-0807381 Spitkovsky无碰撞激波中粒子的加速是宇宙中大多数非热现象模型的核心，包括脉冲星风星云、活动星系核、伽马射线暴和超新星遗迹。 流动能量转化为相对论粒子通常归因于一阶费米机制，但这还没有得到很好的理解。 该项目将通过对天体物理学无碰撞冲击进行首次大规模三维粒子模拟，建立一个冲击加速的自洽理论。 PIC方法是等离子体动力学最基本的从头算方法，能够直接解决等离子体不稳定性，粒子散射和冲击附近磁场产生的复杂微观物理。 需要解决的具体问题包括：1）无碰撞冲击是否会产生能够在下游很远的地方存在的显著磁场？ 2)注入费米机制的冲击粒子的比例是多少？ 3)高能粒子对冲击流体力学和磁场放大有什么影响？ 4)什么机制导致冲击中粒子种类之间的平衡？ 这项研究将是一个决定性的测试流行的假设，即费米加速在碰撞冲击是起源的高能宇宙线和非热粒子在各种天体物理源。结果将具有广泛的意义，观察员，实验学家和理论家参与实验研究高能天体物理和宇宙学的来源。 该研究通过涉及研究生和本科生，博士后，多尺度系统的数值建模和可视化培训来整合研究和教育。 一个分支将是对无碰撞冲击物理学的全面网络介绍。 此外，将在网站上公开发布和支持新版本的并行PIC代码TRISTAN-MP及其分析工具。

AST-0807381SpitkovskyAcceleration of particles in collisionless shocks is at the heart of most models of nonthermal phenomena in the Universe, including pulsar wind nebulae, active galactic nuclei, gamma-ray bursts, and supernova remnants. The conversion of flow energy into relativistic particles is usually attributed to the first-order Fermi mechanism, but this is not well understood. This project will construct a self-consistent theory of shock acceleration by performing the first large-scale three-dimensional particle-in-cell (PIC) simulations of astrophysical collisionless shocks. The PIC method is the most fundamental ab initio approach to plasma dynamics that is able to resolve directly the complex microphysics of plasma instabilities, particle scattering, and magnetic field generation near shocks. Specific questions to be addressed include: 1) Do collisionless shocks generate significant magnetic fields that can survive far downstream? 2) What fraction of shocked particles is injected into the Fermi mechanism? 3) What is the effect of high-energy particles on shock hydrodynamics and magnetic field amplification? 4) What mechanisms cause equilibration between particle species in shocks? This study will be a definitive test of the prevailing hypothesis that Fermi acceleration in collisionless shocks is the origin of high energy cosmic rays and nonthermal particles in a variety of astrophysical sources.The results will be of broad significance to observers, experimentalists, and theorists involved with experiments to study high-energy astrophysical and cosmological sources. The research integrates research and education by involving graduate and undergraduate students, and postdocs, training in numerical modeling and visualization of multiscale systems. An offshoot will be a comprehensive web-based introduction to the physics of collisionless shocks. In addition, a new version of the massively-parallel PIC code TRISTAN-MP and its analysis tools will be publicly released and supported on the web site.