Improved Three Dimensional Nonlinear Theory of Traveling Wave Tubes

A three-dimensional (3D) nonlinear theory of traveling wave tubes (TWTs) is developed, which includes fundamental radio frequency (RF) and harmonic. When the instantaneous bandwidth exceeds octave, the harmonic is generated and the mutual coupling between harmonic and fundamental RF can be observed in TWTs due to nonlinear interaction between electron beam and RF. At low frequencies the harmonic has an obvious effect. Based upon Tien's disc model, a plastic 3D super-particle model is proposed to improve the nonlinear analysis of TWT. Numerical results by employing a periodic magnetic focusing field are presented including voltage sinking.