Research On Long-Range Propagation Of High-Intensity Relativistic Electron Beam In Space Environment

The emission of a relativistic electron beam(REB)in space has important practical applications in active space experiments,by tracing magnetic field lines,probing the middle atmosphere,analyzing beam-particle interactions,and fulfilling other functions.In order to understand multiple reactions and transmission rules of the REB deeply during long-range propagation in the terrestrial atmosphere,this paper is mainly focused on the influence of interactions between the REB and ambient particles according to peculiar characteristics of various environments.By establishing the theoretical model and numerical simulations,the variation of REB during long-range propagation is obtained.According to this,key factors which limit the transmission reach are analyzed.This study may lay the foundation for associated studies on active space based experiments and other practical applications.The main contributions of this work are the following.(1)Both theoretical and numerical simulation calculation models which fit the real atmosphere environment well are proposed.The influence of atmosphere parameters which varies with the altitude on the propagation of REB is revealed.Firstly,based on the actual data of particle densities in the atmosphere and geomagnetic field at different altitudes,parameters in envelope equations are modified and a theoretical calculation model which could reflect the variation of parameters with the altitude is established.Envelope radius,energy loss caused by both inelastic collisions and bremsstrahlung emissions,and beam divergence are calculated accordingly.Secondly,based on actual data of 3-D geomagnetic field and space environment,a Monte-Carlo model which can be used to calculate the long-range propagation of REB is established.Modified envelope equations are used as an approximate solution to verify the results of MC simulations.At last,the MC model is used to simulate the propagation when the beam is both along and perpendicular to geomagnetic field.And the calculation of which the theoretical model is not applicable is achieved in this way.(2)By calculating the propagation trace and beam spot,fine-scale data during the long-range propagation of REB is obtained and the formation mechanism of beam spot is explored.By using 3-D MC simulations,the calculation model of the beam spot which is formed after the long-range propagation of REB is established.The propagation is simulated when the REB is emitted with a certain pitch angle in the altitude range of 300-200 km.According to clear results of Larmor precessions,the effect of initial pitch angle,initial energy,gyro-phase and other beam parameters on the propagation trace is revealed.Influence created by parameters of the beam as well as environment on both the location and shape of the beam spot is also analyzed.Based on features of Larmor precessions of the REB,key factors which determine the location and shape of beam spot are further concluded.(3)A PIC simulation model which can be used for the calculation of longrange propagation of REB in space plasma environment is proposed.By using this model,focusing characteristics of the beam in the ion channel are explored,and the transmission rule of REB in the ion channel is also revealed.Taking the effect of numerical noise into consideration,self-generated magnetic field of the REB is added into the static electric model.The moving window technology is also used to address limitations to the transmission reach created by computing resources.In this way,a PIC quasi-electromagnetic model is then proposed for calculating the long-range propagation of REB in space plasma environment.The analytical model of ion channel oscillation is built at the same time.According to these two models,the ion channel oscillation has been studied and results are verified to ensure the reliability of these models.Combining these two models,rules of the ion channel oscillation with various parameters of the beam and environment,and further the influence of ion channel on the propagation of REB,are analyzed.Besides,instabilities of the REB during long-range propagation in ion channel are explored.Limiting factors are summarized finally when REBs with various parameters propagate in the ion channel.It can be concluded that when utilizing the ion channel to achieve longrange propagation of the REB,choosing suitable beam parameters is necessary to guarantee the continuous and stable propagation of REB.(4)A PIC-MCC simulation model which can be used for the calculation of the long-range propagation of REB in neutral gas is proposed.The effect of ionfocused regime on the long-range propagation of REB is obtained.Ways to achieve the self-focused propagation of REB in the atmosphere are also explored.The moving window technology and null interactions for the combination of macroparticles are added in PIC-MCC simulations to save computing resources.In this way,the so-called 2D3V PIC-MCC simulation for calculating the propagation of REB in neutral gas is achieved.The simulation includes multiple physical processes,such as impact ionizations,elastic collisions,secondary electron attachments and so on.Based on the space distribution of beam electrons and secondary particles,the establishment of ion-focused regime as well as the charge neutralization,current neutralization is analyzed.The model has been verified by envelope equations of a sheet beam.It can be concluded that decrease of the pulse width of REB can effectively reduce the influence of instabilities.Building the ion-focused regime will contribute to the self-focused propagation of the REB in the atmosphere.