Study On The Magnet System Of Microwave Tubes

The orientation of this dissertation is to study practical problems arising in the manufacture of microwave tubes. The author intend to find a solution for the computation of non-linear magnetic fields, improve our CAD software, and in addition design a magnet system for a gyrotron.This thesis includes following subjects-computation of non-linear magnetic fields, data processing and visualization, optimization and criterion for magnet designs, designs of magnet system for a gyrotron.The studies base on a Fortran program developed by High Power Microwave Technology and Device Laboratory, IECAS. This program is employed in the computation of magnetic fields in 2D cylindrically symmetric systems. But in the course of magnetic field computation the permeability distribution in soft magnetic materials has to be supposed as known and fixed. When one tries to calculate the permeability distribution the iteration will lose its convergence. The author finds out the reasons for the divergence by means of theoretical analysis combined with numerical experiments. By successful solution of non-linear magnetic fields and revision of the program, we can reach following conclusions: In the computation of nonlinear magnetic fields, if iteration method is used, under-relaxation is necessary when amending the permeability distribution in soft magnetic materials; And when calculating the equivalent current density in permanent magnets, under-relaxation is not a necessity; When searching for permeability values by interpolation method on the demagnetization curve of soft magnetic materials, if a fixed saturation point is set, around this point an abrupt change of permeability values will be obtained; This sudden change may cause a little problem in the smoothness of magnetic field distribution; Because the magnetic circuits of microwave tubes are too complicated, in the author's view, to describe the working state of a magnet system, the working points of magnets can not do it properly but average energy production of magnets will serve; As to indicate the quality of a magnet system design for microwave tubes, the efficiency of magnetic energy utilization will be a very good criterion.