GEM: Anti-Parallel and Component Merging Scenarios in Collisionless Reconnection

最近的工作带来了许多令人惊讶的结果，挑战了许多关于磁重联基本物理的传统观点。该项目将利用粒子-细胞等离子体模拟代码重新检查重连接的物理学。模拟的一个重要方面是它们将使用开放边界模型而不是传统的周期边界条件来运行。这种方法的初步结果似乎很有希望，因为完全消除了周期性边界条件固有的人工再循环。等离子体和磁通量可以根据需要进出系统。由此产生的模拟有效地模拟了一个比周期边界条件下可能的大得多的系统。这些模拟使人们对电子扩散区的结构及其对快速重联的影响有了新的认识。该代码的一个创新之处在于，它已适用于基于细胞的计算机，这种计算机很可能是大规模计算的未来，其预期速度将比现有模拟提高40倍。该项目将研究与地球空间环境建模项目焦点小组相关的磁重联相关的几个重要问题。要研究的具体主题包括：(1)反平行重联与组件合并的相对作用，(2)等离子体湍流对重联速率的作用，(3)重联的开始及其随后的非线性发展对等离子体β参数（等离子体压力与磁压力之比）的依赖，以及(4)重联区域不对称电流片的演变。该项目的教育方面包括支持加州大学圣地亚哥分校的几名本科生参与研究。爱荷华大学的两名研究生也将参与其中。

Recent work has led to a number of surprising results that challenge many of the conventional viewpoints regarding the essential physics of magnetic reconnection. This project will re-examine the physics of reconnection utilizing a Particle-In-Cell plasma simulation code. An important aspect of the simulations is that they will be run using an open boundary model rather than the traditional periodic boundary condition. The initial results from this approach appear quite promising since the artificial recirculation that is inherent with periodic boundary conditions is completely eliminated. Plasma and magnetic flux is allowed to enter and exit the system as needed. The resulting simulations effectively mimic a much larger system than is possible with periodic boundary conditions. These simulations have led to a new understanding of the structure of the electron diffusion region and its effect on fast reconnection. An innovative aspect of the code is that it has been adapted for cell-based computers which are likely to be the future of large-scale computations with expected speed gains of a factor of 40 over existing simulations. The project will examine several important questions related to magnetic reconnection that are relevant to the Geospace Environment Modeling program's focus groups. The specific topics to be investigated include: (1) the relative roles of anti-parallel reconnection versus component merging, (2) the role of plasma turbulence on the rate of reconnection, (3) the dependence of the onset of reconnection and its subsequent nonlinear development on the plasma beta parameter (the ratio of the plasma pressure to the magnetic pressure), and (4) the evolution of asymmetric current sheets in the reconnection region.The educational aspects of the project includes support for several undergraduate students at UCSD to participate in the research. Two graduate students at the University of Iowa will also be involved.