Studies Of Magnetic Reconnection By Using PIC Simulation

Magnetic reconnection is a mechanism that converts the free energy stored in the magnetic field into plasma thermal energy and kinetic energy.It is widely used in space physics and laboratory physics.Due to the complicated process of magnetic reconnection,its occurrence conditions and physical mechanisms need to be further explored.In this paper,the collisionless magnetic reconnection process is studied using the 2.5-dimensional particle simulation method,and the following results are obtained:Without guiding field,it is found that the reconnection electric field has a circular distribution and there are two symmetrical extreme points.The electrons flow to the X point along the magnetic field line outside the separation line,and flow out of the reconnection region along the separation line,forming a in-plane Hall current,and B_y exhibits a quadrupole structure distribution.In the ion diffusion region,the reconnection electric field is mainly composed of the Hall term in the generalized Ohm’s law;in the electron diffusion region,since the electrons are also decoupled from the magnetic field lines,the Hall term approaches zero,and the reconnection electric field near the X point is almost exactly equal to the electron’s pressure tensor gradient term.In the presence of a strong guiding field,the velocity of electrons flowing to X point along the outside of the separation line of the first and third quadrants increases,the velocity of electrons flowing out of X point along the separation line of the second and fourth quadrants decreases,and the original quadrupole structure of B_y is destroyed,the B_y positive region becomes larger and occupies almost the entire magnetic island,and the negative region becomes smaller and almost only appears on the thin layer near the separation line.In the presence of a strong guiding field,the development speed of magnetic reconnection is significantly slower than without a guiding field,and the reconnection rate decreases significantly.The reconnection rate decreases with the increase of the guiding magnetic field.The effect of electron temperature on the reconnection rate is divided into two stages.When the electron temperature is less than a certain value,the reconnection rate is positively correlated with the electron temperature,while when the electron temperature is greater than this value,the reconnection rate is negatively correlated with the temperature.An increase in ion temperature always leads to a decrease in the peak reconnection rate,which acts as an inhibitor.The effect of non-uniform temperature distribution of electrons and non-uniform ions on magnetic reconnection is reflected in the different action ranges of E_z,and electrons mainly produc a strong E_z electric field near the reconnection region on the high temperature side.while ions mainly act near the magnetic island,forming a layer of E_z with a relatively large area outside the magnetic island.