Axisymmetric Periodic Permanent Magnet Focusing System Two-dimensional Finite Element Analysis

Microwave tubes is a kind of vacuum electron devices and it is widely used in modern military electronic equipments. Magnetic system plays an important role in the development of microwave tubes. Periodic permanent magnetic field focusing system has proved to be an useful method of focusing system in microwave tube. Therefore the study of periodic permanent magnetic field focusing system plays an important role in the development of present-day microwave tube. The development of microwave tubes depends largely on modeling and simulation technology because the manufacture of microwave tubes is quite complicated involved in many disciplines and process design is extremely complex. Many countries are working on the development of microwave tubes CAD technology. 2D finite element method is used to study periodic permanent magnetic focusing system in this context.This paper focuses on 2D linear finite element method and 2D second-order finite element method for axisymmetric periodic permanent magnetic focusing system. 2D linear finite element has the advantage of simple formulas, but its accuracy is poor and its convergence is slow, and magnetic induction within each grid is constant. Then the theory of periodic permanent magnetic focusing system is studied. 2D second-order finite element method is used to simulate magnetic displacement of axisymmetric permanent magnetic models in cylindrical coordinates.First the single magnetic ring model and the single period model are simulated. These results are compared with the results of Ansoft Maxwell 2D and UESTC-PPM. 2D second-order finite element method is more accurate. Then the convergence is compared between linear finite element method and second-order finite element method. Second-order finite element method has better convergence and faster convergence rate. Finally 2D second-order finite element method can meet the engineering needs.