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.
