A three-dimensional nonlinear beam–wave interaction theory for common traveling wave tubes

Abstract

A three-dimensional (3-D) nonlinear theory model of beam–wave interaction for common traveling wave tubes (TWTs) is described. The equation governing the amplitude of electromagnetic wave is derived analogously to Poynting’s theorem. The electron dynamics are treated using the 3-D Lorentz force equations. RF space charge fields are obtained from solutions of the Helmholtz equations. In the model, the RF field profiles for cold structure are represented by the digitized RF field calculated by a finite-element software, HFSS. Because the digitized RF field can be obtained in the same way, the 3-D simulation code can be used to simulate common TWTs, such as helix TWTs, coupled-cavity TWTs, and even the folded waveguide TWTs. Results from the 3-D code are compared with those from 1-D code, experiment and the existing analytical theories for three types of slow wave structures.

Keywords:

• 3-D nonlinear theory
• traveling wave tubes
• beam–wave interaction
• digitized field

Acknowledgments

The authors would like to express gratitude to Professors Jin-Jun Feng, Xian-Ping Wu and Yin-Fu Hu in Beijing Vacuum Electronics Research Institute for the experimental tests of the FW TWT.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the National Natural Science Foundation of China [grant number 61201003], [grant number 60931001], [grant number 61071030].