| Magnetic reconnection, the process by which magnetic energy in sheared magnetic field configurations is converted into heat and flow energy, is believed to be a very important process in space physics, providing the energy for phenomena such as substorms and solar flares. In the magnetosphere and some other physical systems where reconnection is believed to occur, however, the plasma is collisionless, making the traditional resistive models inadequate. In a collisionless plasma, the frozen-in constraint can be broken when the length scale of variation of the magnetic field becomes comparable to the orbit size of the particles which constitute the plasma. Due to the disparate masses of the ions and the electrons, the region where the frozen-in constraint is broken develops a two-scale structure: a larger scale associated with the ions, and an inner scale associated with the electrons. For much of this region, whistler physics, where the electrons are frozen-in while the ions are not, can be used to describe the dynamics. The nature of whistler physics and its effect on a quasi-steady reconnection. process is the topic of this thesis. First, the inner electron dominated region where the ion velocities are negligible is examined using a full particle electron code where the ions are treated as an unmoving, charge-neutralizing background. Because the whistler velocity increases for smaller scale size, it is found that the process breaking the frozen-in constraint does not constrain the reconnection rate. The reconnection process for large system sizes is also studied using a hybrid code, where the electrons are treated as a fluid with mass, and the ions are treated as individual particles. It is found that the reconnection rate is independent of system size, very different from resistive MHD reconnection. The whistler physics is once again the key. The rapid whistler motion of the frozen-in electrons generates large electric fields which accelerate the outflowing ions to their Alfven speed in a finite distance. The reconnection rate is found to be a universal constant on the order of 0.1 cA. |
