Numerical Simulations of Magnetic Reconnection in an Asymmetric Current Sheet

【摘要】 Previous particle-in-cell simulations have shown that electron phase-space holes(electron holes),where the associated parallel electric field has a bipolar structure,exist near the four separatrices in anti-parallel magnetic reconnection.By performing two-dimensional(2-D)particle-in-cell(PIC)simulations,here we investigate magnetic reconnection in an asymmetric current sheet,with emphasis on the parallel electric field near the separatrices.Compared with magnetic reconnection in a symmetric current sheet,it is found that the parallel electric field with a bipolar structure only exists around the separatrices in the upper region with a lower density(upper separatrices).Such a bipolar structure of the parallel electric field is considered to be associated with electron holes resulting from the nonlinear evolution of the electron beam instability excited by the high-speed electron flow formed after their acceleration around the X line.The disappearance of the parallel electric field around the separatrices in the lower region with a higher density(lower separatrices)may be due to the transverse instability,which is unstable in a weak magnetized plasma.更多还原

【Abstract】 Previous particle-in-cell simulations have shown that electron phase-space holes(electron holes),where the associated parallel electric field has a bipolar structure,exist near the four separatrices in anti-parallel magnetic reconnection.By performing two-dimensional(2-D) particle-in-cell(PIC) simulations,here we investigate magnetic reconnection in an asymmetric current sheet,with emphasis on the parallel electric field near the separatrices.Compared with magnetic reconnection in a symmetric current sheet,it is found that the parallel electric field with a bipolar structure only exists around the separatrices in the upper region with a lower density(upper separatrices).Such a bipolar structure of the parallel electric field is considered to be associated with electron holes resulting from the nonlinear evolution of the electron beam instability excited by the high-speed electron How formed after their acceleration around the X line.The disappearance of the parallel electric field around the separatrices in the lower region with a higher density(lower separatrices) may be due to the transverse instability,which is unstable in a weak magnetized plasma.更多还原