2012-03-27
| Prof. Quanming Lu |
| Department of Geophysics and Planetary Science, University of Science and Technology of China, Hefei, China |
| Time: 2:00 pm, March 27, 2012 |
| Place: lecture room 616, physics building |
| Abstract: An extended current sheet may be unstable to secondary magnetic islands in the vicinity of the X line, and these islands can dramatically influence the reconnection rate. We first perform two-dimensional particle-in-cell simulations to investigate the evolution of the electron current sheet (ECS) in guide field reconnection. The ECS is formed by the electrons accelerated by the inductive electric field in the vicinity of the X line. The ECS is then extended along the direction due to of the imbalance between the electric field force and the Ampere force. The tearing instability is unstable when the ECS becomes sufficiently long, and several seed islands are formed. These tiny islands may coalesce and form a larger secondary island in the center of the ion diffusion region. We also observational evidence of such a secondary island near the center of an ion diffusion region, which is consistent with the action of the secondary island instability occurring in the vicinity of the X line. In the island, the electron density peaks in the outer region while the dip is in the core region with a strong core magnetic field. The electron density dip in the core region is formed due to the existing strong core field which expels electrons out of the core region. The electron flat-top distributions are detected in the ion diffusion region except the core region of the island, and the shoulder energy range of the flat-top distributions is from 100eV to 4keV. An enhancement of the energetic electron flux up to 200keV is found in the ion diffusion region, and a further increase of energetic electron fluxes is observed inside the island. |
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