Particle Acceleration in Astrophysical Collisionless Shocks

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。流能向相对论性粒子的转换通常归因于一阶费米机制，但这并没有得到很好的理解。该项目将通过对天体物理无碰撞冲击进行首次大规模三维粒子池（PIC）模拟，构建一个自一致的冲击加速度理论。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、粒子散射和近冲击磁场产生等复杂的微物理问题。需要解决的具体问题包括：1)无碰撞冲击是否会产生可以在很远的下游存活的显著磁场？2)多少激波粒子被注入费米机制？3)高能粒子对激波流体力学和磁场放大的影响是什么？4)冲击中粒子间的平衡机制是什么？这项研究将是对普遍假设的决定性测试，即无碰撞冲击中的费米加速度是高能宇宙射线和各种天体物理源中的非热粒子的起源。这些结果将对参与高能天体物理和宇宙学源实验研究的观测者、实验学家和理论学家具有广泛意义。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，将研究和教育结合起来。一个分支将是一个全面的基于网络的介绍无碰撞冲击的物理。此外，新版本的大规模并行PIC代码TRISTAN-MP及其分析工具将在网站上公开发布和支持。

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.