1. 学术报告：Inflow density influence of magnetic 时  间：2011-11-10（ 星期四）下午15:30 地  点：教学行政楼1514会议室 主  题：Inflow density influence of magnetic reconnection 报告人：吴频博士 单  位：特拉华大学 摘  要：Inflow density influence of magnetic reconnection.Abstract:We perform a systematic study of the effect of inflow density onreconnection diffusion regions using a 2.5-D particle-in-cell (PIC) code.The diffusion region structures are analyzed at times when allsimulations have reconnected the same amount of magnetic flux.We find that reducing the inflow density from 1 to 1/100th of thecurrent sheet density dramatically increases the diffusion regionphysical size and the reconnection rate. The width of the diffusionregion scales with the upstream ion inertial length systematically.Consistent with the presence of counter-streaming inflowing ion beamsnear the x-line, the ion meandering width in the diffusion regionalso scales with the ion inertial length. The aspect ratio of theion diffusion region remains a constant, independent of the inflowdensity. The quadrupole Hall magnetic field is reduced. Theupstream magnetic field deviates from its asymptotic value by$\sim 50\%$ at the lowest simulated inflow density. The downstreamion outflow velocity scales linearly with the upstream Alfv\'enspeed with a multiplication factor $\sim 0.4 <1$. When appliedto magnetic reconnection in the Earth's magnetotail, this factorof 0.4 is a possible explanation as to why bulk flow velocitiesin the magnetotail are typically on the order of 500 km/s, whilethe Alfv\'en speeds of inflowing plasmas can exceed 2000 km/s.In addition, we find the downstream dipolarization front (DF)is a moving ram that pushes and compresses the initial equilibriumplasma sheet in front of it. The DF propagation scales with theupstream Alfv\'en speed, leading to faster, steeper, and morecompressed DFs with stronger $B_{z}$ at low lobe densities.These DFs reflect plasma sheet ions in a streaming manner.The streaming ions create a bipolar magnetic field straddlingthe central plasma sheet and can excite various instabilities. [1] [2] [3] Download images (local images only) as a tar.gz pack: Full Size Small Size

李勤秀 Posted at 2011-11-01 08:01 CST Last modified at 2011-11-11 17:11 CST Link to this poster Top