Collisionless Magnetic Reconnection

这个项目将集中于了解弱碰撞系统中重联的开始，以及湍流和反常电阻率对磁重联的影响。在弱碰撞系统中，对于给定的等离子体碰撞性，存在两个重联解，一个是慢的Sweet-Parker解，一个是快的霍尔重联解。在临界电阻率以下，Sweet-Parker溶液消失，重联率突然增加许多数量级，达到快霍尔率。到目前为止，对这一灾难性转变的模拟仅限于反平行重新连接的情况。这个项目将通过包括引导磁场来扩展过渡的建模。此外，还将采用以物理学为基础的、半解析的过渡模式。将解析模型与数值模拟结果进行比较。专门的实验室重联实验和地球磁层中的卫星观测有大量证据表明，在无碰撞磁重联期间，在x线附近和沿磁分离驱动的强电流区域是动荡的。湍流的存在或不存在与局部电子β参数(等离子体压力除以磁压之比)有关。如果电子β较低，则携带大部分重联驱动电流的电子的流动速度将超过局部电子的热速度。在这些条件下，将出现流动不稳定性，产生异常的电阻率，从而打破流动冻结条件。该项目将检查具有不同电子β值的2-D模拟，并将测试电子分布对流动不稳定性的稳定性。一个关键的问题是，局部电子加热是否足够强，足以抑制这种不稳定性。在已经建立了不稳定性的区域，将完成对这种湍流发展的三维模拟，以确定由此产生的湍流和异常电阻率的β相关性。

This project will focus on understanding the onset of reconnection in weakly collisional systems and the impact of turbulence and anomalous resistivity on magnetic reconnection. In weakly collisional systems, two reconnection solutions exist for a given plasma collisionality, a slow Sweet-Parker solution and a fast Hall reconnection solution. Below a critical resistivity the Sweet-Parker solution disappears and the reconnection rate abruptly increases by many orders of magnitude to the fast Hall rate. Up to this point the modeling of this catastrophic transition has been limited to the case of anti-parallel reconnection. This project will extend the modeling of the transition by including a guide magnetic field. In addition, a physics-based, semi-analytic model of the transition will be pursued. The analytic model will be compared with the results of numerical simulations. There is substantial evidence from dedicated laboratory reconnection experiments and satellite observations in the Earth's magnetosphere that the regions of intense current that are driven near the x-line and along the magnetic separatrices during collisionless magnetic reconnection are turbulent. The presence or absence of turbulence is linked to the local electron beta parameter (the ratio of the plasma pressure divided by the magnetic pressure). If the electron beta is low, the streaming velocity of electrons, which carry most of the reconnection driven current, will exceed the local electron thermal velocity. Under these conditions, streaming instabilities will arise, producing anomalous resistivity that breaks the frozen-in-flux condition. The project will examine 2-D simulations with differing values of the electron beta and the electron distributions will be tested for stability to streaming instabilities. A critical question is whether local electron heating is strong enough to inhibit such instabilities. In regions where instability has been established 3-D simulations of the development of this turbulence will be completed to determine the beta dependence of the resulting turbulence and anomalous resistivity.