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Abstract: Magnetic reconnection is a physical process in plasmas that converts magnetic energy into plasma kinetic energy and thermal energy. It plays an important role in the generation of the solar flare, interactions between the solar wind and Earth's magnetosphere, and magnetic confinement fusion devices. This thesis focuses on applications in space plasmas using numerical simulations.

The classical Sweet-Parker solution has an elongated current sheet that is too slow to explain solar flares, while the Petschek solution has a shorter current sheet and a faster reconnection rate. It is proposed that the resistivity gradient around the diffusion region is essential for the Petschek model to exist, and a spatially-localized resistivity has been implemented in magnetohydrodynamics (MHD) simulations to achieve Petschek reconnection. We found that a simple resistivity gradient along the outflow direction can also generate Petschek-type reconnection in MHD simulations. This finding has possible applications in solar spicules formation or plasma thrusters. 

Another important application of magnetic reconnection is in Earth’s magnetotail, which is critical to the energy release during geomagnetic substorms. Because of the finite extension of Earth’s magnetosphere, magnetic reconnection in the magnetotail is intrinsically three-dimensional. In this thesis, we also study magnetic X-line spreading in the current direction using three-dimensional PIC simulations. We found that X-line spreading is affected by drift-kink instability. This finding is important for modeling energy transport into Earth's magnetosphere via reconnection in Earth's magnetotail.

Graduate Advisor: Professor Yi-Hsin Liu

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