Analysis of static trajectories in traveling wave tubes

The ripple of static trajectories focusing by the uniform solenoidal magnetic field and periodic permanent magnetic(PPM) field has been studied. the period and the amplitude of the ripple by the two kinds of field has been concluded. The effect of the magnetic field strength has been discussed. The small wavelet by PPM field has been reasoned out, whose period is a half of the PPM field period. The ripple of static trajectories by PPM field is nearly equivalent to the one by solenoidal magnetic field superposing the small wavelet. The ripple has been proved by 3D beam-wave interaction simulator(BWIS) module of microwave tube simulator suite(MTSS),which was developed by University of Electronic Science and Technology of China.