Simulation Study of the Causes of Plasmoid Acceleration and the Changes of Magnetic Reconnection Rate in Resistive MHD Plasmas
| Autor: | Hsiu-Shan Yu, 余秀珊 |
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| Rok vydání: | 2011 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 99 Prominence/filament eruptions and coronal mass ejections (CMEs) usually show an initial acceleration followed by a nearly constant propagation speed. Concerning about solar flares, it is a local feature in comparison with global feature of the initiation of CME. The magnetic reconnection rate deduced from the foot point motions of the solar flares and the magnetic field component normal to the solar surface and the acceleration of filament/CME show a good temporal correlation [Zhang et al., 2001; 2004; Qiu et al., 2004; Jing et al., 2005]. In this thesis, a two-dimensional resistive magnetohydrodynamic (MHD) simulation is carried out to study (1) the time evolution of the magnetic reconnection and its relation to the acceleration of plasma flow, (2) the forces that lead to the acceleration of the plasma and the plasmoid, and (3) the rate of magnetic flux variation effects on the reconnection rate. Our results show that the fast flows are not limited to the direction perpendicular to the local magnetic field. The fast parallel flows are accelerated by the parallel component of the pressure gradient force. The net force perpendicular to the magnetic field can accelerate the plasma and the plasmoid along the current sheet. The acceleration of the plasmoid is also controlled by the mass contained in the plasmoid. We found that the magnetic reconnection in MHD plasma is due to the non-uniform magnetic annihilation rate along the current sheet. The reconnection/reconfiguration site does not necessary stay at the neutral point. It can move with the Y-line next to the bifurcated current sheets. We also found that the fast ejection of the plasmoid can stretch the current sheet and consequently reduce the magnetic reconnection/reconfiguration rate temporally before a new plasmoid is formed. A mutual coupling theory of magnetic reconnection and acceleration of plasmoid is proposed: the magnetic tension force resulting from the magnetic reconnection will lead to the acceleration of plasmoid; however, the acceleration of plasmoid can stretch the current sheet and reduce the magnetic reconnection rate. But the stretched thin current sheet is favorable for the formations of small scale plasmoids. We also found that the speed of the plasmoid increases with decreasing the size of the plasmoid. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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