Design of new structure of transition region for periodic permanent magnetic focusing

Considering that generation and maintain of small radius, high power beam is restricted by the compression ratio of electron gun, the effect of magnetic field on electron trajectories in transition region was analyzed. A method was presented to compress the beam by changing the magnetic field in transition region gradually. Compared with the traditional one, the method requires lower compression of electron gun while providing small radius beam for interaction, it also optimizes the beam quality. The method was used to simulate an electron optical system for Ku-band 6 kW TWT, some good results are obtained.