Research On Time Domain Numerical Calculation Method Of Electromagnetic Wave Propagation In Plasma

When hypersonic vehicles reenter the atmosphere or fly on a long voyage,the existence of the plasma sheath will affect the navigation,communication,and measurement and control performance of the aircraft,and in severe cases,it will produce communication "black barrier"effect.To overcome and even solve this problem,it is necessary to deeply study the electromagnetic wave propagation in plasma.The numerical calculation method is used to study the electromagnetic wave propagation in plasma medium,which has the advantages of strong versatility,low research cost and short cycle time.In the numerical calculation methods of electromagnetic wave propagation in plasma,the advantage of the time-domain method is its wide-band characteristics,that is,by exciting a wide-band pulse wave,the response within the entire frequency band can be obtained in one calculation.In particular,the finite-difference time-domain(FDTD)method has been widely used in the study of electromagnetic wave propagation in plasma in recent years due to its simple calculation,intuitive,easy to implement,and the broadband electromagnetic response can be simulated by the single simulation.However,the numerical stability of the FDTD method is limited by the minimum space step and depends on the media parameters.As a result,the calculation time step of the electromagnetic problem in plasma with fine structure model is very small,and the calculation time is long and difficult to be realized.Therefore,the FDTD method with good numerical stability or even unconditional stability is studied to improve the computational efficiency of plasma FDTD method,which is of great guiding significance and application value for the rapid prediction of radio wave propagation characteristics in plasma,as well as the rapid suppression,overcoming and even solving the communication "black barrier" problem of aircraft reentry.The main content and innovation for this paper are as follows:1.A magnetized plasma finite-difference time domain(FDTD)method based on Bilinear Transform(BT)is proposed,which has higher calculation accuracy and better stability.Firstly,the implementations of several typical non-magnetized and magnetized plasma FDTD methods are introduced.Numerical dispersion characteristic and stability of plasma FDTD methods are analyzed by taking the plasma JEC-FDTD as an example.Secondly,a magnetized plasma FDTD method based on Bilinear Transform(BT)is proposed.It is verified that the magnetized plasma BT-FDTD method has higher calculation accuracy and better stability by comparison with the auxiliary differential equation FDTD(ADE-FDTD)method,exponential time difference FDTD(ETD-FDTD)method and analytic method.Finally,in order to improve the computation speed of the method,parallel acceleration based on CUDA architecture is implemented.2.The unconditionally stable FDTD method based on the weighted laguerre polynomials(WLPs)is studied,and an SC-PML absorption boundary implementation for tridiagonalized WLP-FDTD method is proposed.Firstly,WLPs and its property are introduced,and the iterative formula of the unconditionally stability WLP-FDTD method is is derived.Secondly,the iterative formula of SC-PML with complex frequency-shifted(CFS)factor for WLP-FDTD method is deduced.As a result,the method can solve the electromagnetic radiation problem with high precision.Finally,an SC-PML implementation for the tridiagonalized and efficient WLP-FDTD method is proposed,and the iterative formula for calculating electromagnetic field is derived,so that the method can simulate the electromagnetic problem with open domain efficiently.Numerical examples demonstrate the high efficiency of the method.3.A variety of unmagnetized plasma WLP-FDTD method is proposed.Firstly,a two-dimensional unmagnetized plasma WLP-FDTD method is proposed,and the electromagnetic problems in the unmagnetized plasma dispersion medium are treated by using the polarization current density component and the electric field component in the same space grid.Secondly,a two-dimensional unmagnetized plasma WLP-FDTD method is proposed,and the iterative formula of SC-PML absorption boundary for WLP-FDTD method is derived.Numerical examples show that the method is correct,accurate and efficient,and the absorption performance of SC-PML absorption boundary with CFS factor is better than that of the nearly PML.Finally,the unmagnetized plasma two-dimensional efficient WLP-FDTD method is extended to three-dimensional,and the correctness and high computational efficiency of the method are verified by the numerical examples of electromagnetic wave scattering from cubic plasma.4.A variety of anisotropic magnetized plasma WLP-FDTD method is proposed,which enables the unconditionally stable WLP-FDTD method to be popularized in anisotropic media for the first time.Compared with the traditional FDTD method,the calculation speed of this method is faster,and the improvement of this speed is more obvious when the model has fine structure.Firstly,starting from a simple one-dimensional problem,a one-dimensional magnetized plasma JEC-WLP-FDTD method is proposed,and the SC-PML absorption boundary condition is introduced into the method,so that the method can accurately and efficiently calculate electromagnetic problems in the magnetized plasma with open domain.Secondly,a magnetized plasma tridiagonalized highly efficient JEC-WLP-FDTD method is proposed for one-dimension.The sparse matrix equation is converted into the tridiagonal matrix equation by introducing the factorization scheme into the JEC-WLP-FDTD method,which improves the computation speed of the method.Then,a two-dimensional JHC-WLP-FDTD method with current density and magnetic field components in the same space position is proposed,and the iteration formula of SC-PML absorption boundary for this method is derived.The transient evolution of electromagnetic field when a plane wave is incident on a magnetized plasma cylinder is analyzed.Finally,the JHC-WLP-FDTD method is proposed to solve the more practical electromagnetic problems in magnetized plasma for three-dimension,and the SC-PML absorption boundary is introduced into the method.Numerical example shows that the method is correct.