The Influence Of Guide Fields On The Asymmetry Of Reconnection Structure During Fast Reconnection

Magnetic reconnection is widely exists in space plasma and laboratory plasma, which is an important plasma physical mechanism. It starts at diffusion region in micro-scale, and then changes the topological structure of magnetic field lines in macro-scale, along with the fast energy release and transport. Space plasma is collisionless, which means that mean free path of plasma is much larger than characteristic length. As is well known, most of magnetic reconnections in solar-terrestrial space are fast Hall reconnections, which have fast energy releasing speed. A remarkable features of fast Hall reconnection is quadrupolar magnetic field and electric field around diffusion area, and it is widely used to qualify diffusion area in satellite observation.In the study of magnetic reconnection, the out-of-plane magnetic field component is usually set zero in the model, which means guide field is zero. And the guide field is considered purely linear superposition with Hall magnetic field in the presence of guide field. According to recent studies,the out-of-plane quadrupolar magnetic field in fast magnetic reconnection is not purely linear superposition with guide field, but is distorted in the presence of guide field. It is asymmetric with respect to the current sheet. In this paper, we analyze the spatial and amplitude asymmetry of Hall magnetic field By and Hall electric field Ez in reconnection with different guide fields by a series 2.5-D particle-in-cell simulations. We find that By field is distorted by guide field, becoming non-axisymmetric. And the ratio between |min(By)| and |max(By)| increases as the growth of guide field and then becomes stable. And the ratio between |max(Ez)| and |min(Ez)| at the point near X-point increases as the growth of guide field and then becomes stable, but it stay stable from the beginning to end at the point far away from the X-point. In addition, we find that Ez becomes tripolar because of a new negative pole appearing, and its absolute value of minimum of new negative pole increases as the growth of guide field and then tend to stable. At last, by analyzing the different terms in the generalized ohm’s law, we find that electric field Ez is mainly balanced by the Hall term, and the amplitude asymmetry is mainly caused by the Hall effect. At the place near X-point, appearing of new negative pole is mainly caused by convective term; while at the place far away from X-point, it is caused by Hall term and convective together.