Design of electron optics system of electron gun for millimeter-wave TWT

An electron gun and a magnetic-focus system for folded waveguide millimeter-wave traveling wave tube(TWT) were designed by electron gun code(VBGUN) based on visual boundary element method and magnetic field code(MOM) based on boundary element method. A definition of relative coefficient was used to optimize parameters, and a sensitive coefficient was defined to review the effect of fabrication-errors. The design results show that this kind of gun is easily affected both by the shape of the electrodes and the fabrication-errors. The maximum magnetic field on axis is limited by the dimension of the slow wave structure. This is the main problem for the focus system design of the folded waveguide TWT, which can be solved by augmenting the working voltage or decreasing the beam current. Consequ