A Method To Reduce Plasma Sheath Electron Density Using Pulse Magnetic Field

When hypersonic vehicle flying in the atmosphere with a speed exceed 7 Mach,the plasma sheath is formed on the surface of the aircraft will lead to the communication blackout,This phenomenon seriously affects the positioning,tracking,navigation and other functions of the ground station to the aircraft,so as to cause a series of dangers,such as the unknowable flight state,the telemetry data agnostic,and so on.Some studies show the blackout is closely related to the high electron number density and collision frequency in plasma sheath.Aim at this problem,this article expounds a method of using pulsed magnetic field to reduce the local plasma density.By setting the appropriate magnetic field,the moving direction of charged particles in the plasma is deflected,thus producing a low electron density region and improving the transmittance of the electromagnetic wave in this position.The main research contents are as follows: 1.A theoretical model for the change of electron density in dynamic plasma under pulsed magnetic field is established.Firstly,combing the study of the particle diffusion coefficient in the unmagnetized plasma,the particle diffusion coefficient in the magnetized plasma with anisotropic properties is derived and applied to the particle motion based on the drift diffusion theory.Secondly,the mathematical relationship of the coupling between the pulsed magnetic field and the dynamic plasma is proposed from the magnetohydrodynamics theory.Ultimately,a complete mathematical solution model is established to solve the problem of real time distribution of particles in a dynamic plasma under pulsed magnetic field.2.A simulation model of dynamic plasma electron density under pulsed magnetic field is established.Based on the mathematical model,the simulation model of dynamic plasma electron density under pulsed magnetic field is established by using COMSOL multi physics simulation software.Analyzed the distribution and time evolution of electron density in the plasma under different parameters,the results show that pulsed.Magnetic field has a weakening effect on plasma density,and the weakening effect is proportional to the intensity of magnetic field,and it’s inversely related to the velocity,and the electron density of the plasma.3.The electromagnetic wave propagation model in plasma under different magnetic field is established.The propagation model of electromagnetic wave in plasma under constant magnetic fields established firstly,and the transmission characteristics of electromagnetic waves under constant magnetic field are analyzed and calculated.Then,based on the pulsed magnetic field weakens the electron density of the plasma,a 3D simulation model of pulse electromagnetic wave propagation in plasma in a magnetic field is established with COMSOL Multiphysics simulation software.This thesis contrasts the transmission coefficients at no magnetic field,constant magnetic field,and pulsed magnetic field.The results show that applying pulsed magnetic field has the best effect to improve the transmission coefficient of low frequency electromagnetic wave in plasma.Meanwhile,pulsed magnetic field has the advantages of low load,short actuation duration and little interference on aircraft electronic equipment,etc.The research results of this paper show that using pulsed magnetic field to weaken plasma electron density is an effective way to alleviate the communication blackout.