Periodic permanent magnet focusing system for multi-beam traveling wave tube

Periodic permanent magnet focusing system for five-beam traveling-wave tube has been studied using the 3-D traveling-wave tubes simulation code developed by ourselves. Static magnetic field and beam transmission characteristics were analyzed . and the transverse magnetic field inside the outer beam tunnels and their effect on beam transmission were described. The results show that the PPM focusing system has good magnetic distribution and beam focusing capacity, when its structure is properly designed, the transverse magnetic field has little effect on outer tunnel beam transmission.