This paper reports the development of a 3-D finite-element design tool for the design of permanent-magnet focusing system called the magnetic focusing simulator (MFS). It is a new module of microwave-tube simulator suite developed by the University of Electronic Science and Technology of China. MFS specifically targets problem classes including periodic permanent magnet, wiggler, permanent-magnet quadrupoles, periodic cusped magnet, and so on. MFS is a finite-element code of magnetic scalar potential and is a solver of magnetostatic field. It can be used for designing, optimizing, testing, and validating the permanent-magnetic focusing systems. The theory of MFS is discussed in detail in this paper. Besides, the accuracy is compared with the commercial software ANSYS Maxwell, and the performance of MFS is also shown.

Plasma surrounding a hypersonic vehicle can lead to the absorption of incoming radar radiation or the interruption of communication. Therefore, the development of hypersonic vehicle relies on a clear understanding of the strong interaction between the surrounding plasma and the incident electromagnetic wave. However, because of the presence of complex geometrical features and heterogeneous media, these applications are often multiscale. The modeling of such applications in three-dimension (3D) is extremely challenging for traditional numerical methods. In this work, an efficient Discontinuous Galerkin Time-Domain (DGTD) method for the 3D modeling of plasma surrounded hypersonic vehicles is presented. To overcome the grid-induced stiffness problem arising from the modeling of such multiscale applications with dispersive media, and to improve the modeling efficiency, a high order exponential-based time integration for the time-domain Maxwell’s equations discretized by DG schemes with a general flux formulation is proposed. This time integration has excellent stability properties in the locally refined part of the mesh and hence enables the usage of larger time steps compared with the explicit time marching scheme. Additionally, the exponential-based time integration is developed to adapt an anisotropic Perfectly Matched Layer for the modeling of open domain problems. Finally, numerical experiments are presented to investigate the accuracy and convergence properties, and to demonstrate the well modeling capability of the proposed method.

The absorbing boundary condition (ABC) is very common to be used to truncate the computational domain in the hybridizable discontinuous Galerkin (HDG) method. However, if solving waveguide transmission problems with multimode scattering, the ABC is not very applicable due to the wave impedances varying with the frequency. Considering the perfectly matched layers (PMLs) boundary can absorb well the outgoing waves, thus this letter presents a new PML application in the implicit HDG time-domain (imHDGTD) method. For PML and non-PML regions, we need to use different Maxwell equations to generate the global linear system, which leads to a completely different assembling process from ABC. For this, we further give specific technologies. Note that this is the first time that the PML is used in HDG. Compared with the explicit discontinuous Galerkin time-domain method, numerical results show its accuracy and efficient performance, which implies that this method would be very useful.

This article presents an accurate and fast thermal analysis method for multistage depressed collectors (MDCs) of traveling-wave tubes using the finite-element method (FEM). In this method, a novel approach named an advanced multigrid nonlinear solver is proposed to significantly reduce the computing cost of thermal analysis of MDCs. Based on this method, a 3-D thermal design tool for MDCs called a thermal simulator (TS) is developed. By modeling the thermal behavior of various MDCs, the TS is validated, and it is found that the TS is much more efficient than the widely used commercial FEM codes, i.e., ANSYS and CST MPS. Moreover, the TS is accurately and seamlessly coupled with our previously developed electron trajectory code. Consequently, by utilizing the TS, the automated electrical-thermal cosimulation of MDCs is realized accurately and efficiently, which would be very useful for the design of high-performance MDCs.