Fast PIC Simulation Research Of New Vacuum Electronic Devices

With the development of modern military technology and national defense electronic equipment,higher requirements are put forward for the performance of microwave vacuum electronic devices,and the development of new vacuum electronic devices is also promoted.Computer simulation software is an indispensable tool in the design of microwave vacuum electronic devices.With high precision and general applicability(no limitation on the structure),the PIC(particle-in-cell)method is very suitable for the simulation of new vacuum electronic devices.However,the computational efficiency of PIC method is very low,which seriously restricts the application of PIC method in the design of vacuum electronic devices.This dissertation studied the fast PIC method to solve the problem of low efficiency.The main contents include the following four parts.In the first part,the conformal finite-difference time-domain(FDTD)method and the fast conformal mesh generation algorithm are studied.Firstly,the basic principle and stability condition of the conformal FDTD method are introduced.Then the conformal mesh generation algorithm based on triangular surface model and OBBTree is improved.The improved algorithm solves the problems of tangent point judgment,intersection point missing and parallel surface boundary in the original algorithm.It lays a foundation of the conformal FDTD simulation for new vacuum electronic devices.In the second part,the simulation method of the input or output waveguide port in new vacuum electronic devices is studied.Firstly,in order to solve the problems of the existing source when applied to waveguide port,a high-precision and high-efficiency transparent source(P-N transparent source)is proposed.Secondly,a two-dimensional four-component or two-component frequency-domain finite-difference methods using conformal mesh are proposed to obtain the waveguide port mode electromagnetic field for the source implementation.Thirdly,the absorbing boundary algrithm with perfectly matched layer is imporved to be applicable for the conformal mesh.Finally,the simulation methods of waveguide ports are verified by two typical microwave window examples.In the third part,the fast PIC method of new vacuum electronic devices is studied.Firstly,according to the PIC process of beam wave interaction in vacuum electronic devices,the methods of the full current electromagnetic field,the zigzag charge-conserving current deposition and the charged particle push are studied,and the GPU parallel acceleration scheme of the corresponding algrithm is proposed.Then,a folded-waveguide structure is simulated by the GPU parallel and CPU serial code,and the results are in good agreement.Meanwhile,the speedup of the GPU parallel code is presented.In the fourth part,three typical new vacuum electronic devices are simulated by the fast PIC software of the research group,BUMBLEBEE 3D.Firstly,the cold cavity field and beam wave interaction of a folded waveguide TWT are simulated respectively.The calculation accuracy of BUMBLEBEE 3D is verified by comparing with the results of CST.Meanwhile,the high-speed performance of BUMBLEBEE 3D is shown by comparing with the excution time of CST under the same calculation platform and simulation parameters.Then the simulation of a double-corrugated-waveguide TWT and an EIK is carried out,which demonstrates the simulation ability of BUMBLEBEE 3D for new vacuum electronic devices.