A particle-in-cell simulation of symmetric reconnection with zero guide field is carried out to understand the dynamics of ions along the separatrices.Through the investigation of ion velocity distributions at differe...A particle-in-cell simulation of symmetric reconnection with zero guide field is carried out to understand the dynamics of ions along the separatrices.Through the investigation of ion velocity distributions at different moments and locations along the separatrices,a typical distribution is found:two counter-streaming populations in the perpendicular direction,with another two populations accelerated into distinct energy levels in the parallel direction.Backward tracing of ions reveals that the counter-streaming cores are mostly composed of ions initially located at the same side of the separatrix,while the other two accelerated populations in the parallel direction are composed of ions crossing through the neutral sheet.Through analysis of energy conversion of these populations,it is found that the ion energization along the separatrix is attributable primarily to the Hall electric field,while that in the region between the two separatrices is caused primarily by the induced reconnection electric field.For the counter-streaming population,the low-energy ions that cross the separatrix twice are affected by both Hall and reconnection electric fields,while the high-energy ions that directly enter the separatrix from the unperturbed plasma are energized mainly by the Hall electric field.For the two energized populations in the parallel direction,the ions with lower-energy are accelerated mainly by the in-plane electric field and the Hall electric field on the opposite side of the separatrix,whereas the ions with higher-energy not only experience the same energization process but also are constantly accelerated by the reconnection electric field.展开更多
Two-dimensional particle-in-cell (PIC) simulation is used to investigate electron dynamics in colli- sionless magnetic reconnection, and the proton/electron mass ratio is taken to be mi /me = 256. The results show tha...Two-dimensional particle-in-cell (PIC) simulation is used to investigate electron dynamics in colli- sionless magnetic reconnection, and the proton/electron mass ratio is taken to be mi /me = 256. The results show that the presence of a strong initial guide field will change the direction of the electron flow. The electron density cavities and the parallel electric field can be found in the electron inflow re- gion along the separatrix, and the electron inflow and density cavities only appear in the second and fourth quadrants. What is different from the results with a smaller mass ratio is that new structures appear in the diffusion region near the X line: (1) Narrow regions of density enhancement and density cavities can be found synchronously in this region; and (2) corresponding to the electron density changes near the X line, the strong parallel electric fields are found to occur in the first and third quadrants. These electric fields perhaps play a more important role in acceleration and heating electrons than those fields located in the density cavities.展开更多
基金supported by the NSFC grants 41821003 and 41974192,by the B-type Strategic Priority Program of the Chinese Academy of Sciences(Grant No.XDB41000000)by the pre-research projects on Civil Aerospace Technologies No.D020103 funded by China’s National Space Administration(CNSA).
文摘A particle-in-cell simulation of symmetric reconnection with zero guide field is carried out to understand the dynamics of ions along the separatrices.Through the investigation of ion velocity distributions at different moments and locations along the separatrices,a typical distribution is found:two counter-streaming populations in the perpendicular direction,with another two populations accelerated into distinct energy levels in the parallel direction.Backward tracing of ions reveals that the counter-streaming cores are mostly composed of ions initially located at the same side of the separatrix,while the other two accelerated populations in the parallel direction are composed of ions crossing through the neutral sheet.Through analysis of energy conversion of these populations,it is found that the ion energization along the separatrix is attributable primarily to the Hall electric field,while that in the region between the two separatrices is caused primarily by the induced reconnection electric field.For the counter-streaming population,the low-energy ions that cross the separatrix twice are affected by both Hall and reconnection electric fields,while the high-energy ions that directly enter the separatrix from the unperturbed plasma are energized mainly by the Hall electric field.For the two energized populations in the parallel direction,the ions with lower-energy are accelerated mainly by the in-plane electric field and the Hall electric field on the opposite side of the separatrix,whereas the ions with higher-energy not only experience the same energization process but also are constantly accelerated by the reconnection electric field.
基金Supported by National Natural Science Foundation of China (Grant No. 40725013)Open Research Program Foundation of State Key Laboratory for Space Weather, Chinese Academy Sciences
文摘Two-dimensional particle-in-cell (PIC) simulation is used to investigate electron dynamics in colli- sionless magnetic reconnection, and the proton/electron mass ratio is taken to be mi /me = 256. The results show that the presence of a strong initial guide field will change the direction of the electron flow. The electron density cavities and the parallel electric field can be found in the electron inflow re- gion along the separatrix, and the electron inflow and density cavities only appear in the second and fourth quadrants. What is different from the results with a smaller mass ratio is that new structures appear in the diffusion region near the X line: (1) Narrow regions of density enhancement and density cavities can be found synchronously in this region; and (2) corresponding to the electron density changes near the X line, the strong parallel electric fields are found to occur in the first and third quadrants. These electric fields perhaps play a more important role in acceleration and heating electrons than those fields located in the density cavities.
