The Effect Of Guide Field On The Energy Conversion During Collisionless Magnetic Reconnection

Magnetic reconnection is widely regarded as the primary driver of many explosive phenomena in the solar-terrestrial space.During the process of magnetic reconnection,magnetic energy is rapidly converted into the kinetic and thermal energy of the plasma.The two fundamental features of magnetic reconnection are the change in magnetic topology and the conversion of energy.However,how the energy conversion varies with different environmental plasma and magnetic field parameters remains an important mystery,especially how the strength of the guide field(2))affects the overall energy conversion in reconnection and the energy conversion and distribution between different components(such as ions and electrons)is currently unclear.To investigate this issue,we used 2.5-D particle-in-cell(PIC)simulations to study the energy conversion in symmetric magnetic reconnection under different guide field strengths.In this study,we analyzed the influence of the guide field on reconnection from two aspects:1.We consider the entire simulation region as a whole and analyze,through spatial and temporal integration,how energy conversion during reconnection is influenced by the guiding field.Based on the simulation results,we have drawn the following conclusions:As the guide field increases,the reconnection rate decreases.When the guide field increases from 0 to 4,the overall energy conversion first sharply decreases(2)< 3),then increases slowly(2)> 3).In all studied guide field reconnections,ions receive more energy than electrons,but ions receive less energy when the guide field is large.When 2)< 3,the energy gained by electrons decreases as the guide field increases,but when 2)> 3,the energy gained by electrons increases as the guide field increases,resulting in enhanced overall energy conversion.In all the cases we simulated,energy conversion is mainly accomplished through currents and electric fields perpendicular to the magnetic field direction,accounting for more than 80% of the total energy conversion.Ion energization also mainly occurs in the perpendicular direction and decreases with the increase of the guide magnetic field.However,when the guide magnetic field is between 3 and 4,the energization of electrons through perpendicular currents and electric fields increases,resulting in an overall increase in electron energization.2.We divided the reconnection system into four sub-regions: the X-line region(XLR),the flux pile-up region(FPR),the reconnection front(RF),and the fore reconnection front(FRF),and analyzed the effect of guide field on energy conversion in these regions.The following conclusions were drawn:Energy conversion mainly occurs in the FPR and RF regions.With increasing guiding fields,there are changes in the energy conversion at RF and FPR,which include:when the guide field is less than 1,the energy conversion in the FPR is higher than that in the RF;when the guide field is between 1.5 and 3,the energy conversion in both regions is similar;and when the guide field is greater than 3,the energy conversion in the RF is higher than that in the FPR.Additionally,in the high guide field regime(2)>3),the energy conversion at the FRF becomes important due to the enhanced electron energy gain through the perpendicular channel.