Theory And Simulation Study On 35GHz Third Harmonic Complex Cavity Gyrotron

This paper was mainly concerned with the nonlinear analysis and simulation of mode competitions and staitup processed in third harmonic complex cavity gyrotron. The nonlinear results were compared with those from linear theory.First, Starting from general transmission line equations with an electron beam source, a self-consistent nonlinear theoretical model for a complex cavity gyrotron with gradual transitions is presented in this paper. The model accounts for mode coupling in the transition region of the complex cavity. The interaction between the electron beam and H61-H62 RE field in the complex cavity for a third harmonic gyrotron is simulated; many calculations are carried out under different cavity dimensions and electron beam parameters.A self-consistent nonlinear theoretical model for the complex cavity gyrotron with abrupt transition is presented in this paper. The model accounts for beam loading effects self-consistently as well as mode coupling in the transition step of the complex cavity gyrotron. A field matching technique is used to treat mode conversion at the cavity step. First based on the general theory of modal expansion techniques, we got the general equations for the modal field expansion coefficients then a large waveguide step is illuminated by two sets of traveling wave from both sides. Then we directly combined out the standing wave amplitudes and their derivatives. The interaction between the electron beam and TE61,TE62 RE field in the complex cavity for a third harmonic gyrotron is simulated; nrany calculations are carried out under different electron beam parametersIn the first place, the multimode nonlinear electron motion equations and the coupling field equations were established to depict the beam-wave circumstances. We discussed in detail the simplifying and evaluation of theinteraction equations, the physical meanings of process of multimode averaging and the methods to study the mode competition and startup process. The effect of monomode efficiency decline caused by eccentricity was studied, and averaging and the methods to study the mode competition and startup process, ~vith starting current of these modes computed from linear theory to explain it.On the wrking condition of UESTC third harmonic complex cavity gyrotron , we caculated the longitudinal field profiles, resonant frequencies and Q values of the working mode and the parasitic one, using a cold cavity model.Then, we studied the mode competition statues and found possible steady states m TE611FE62 and TE14 multimode. After that, we simulated the start-up process and reached the actual steady state in UESTC gyrotmn, taking into account the actual voltage, current and a rising processes.In this paper, some mode competition controlling methods were analyzed, and the suggestion that mode selection could be realized by adopting appropriate voltage rising process was demonstrated. On the basis of the above, mode competition and startup process in eccenttic gyrotmns were studied, and the view that the eccentricity of electron beam would not only declining the interaction efficiency, not only even aggravate mode competition in gyrotrons, but also would possibly vitiate the mode competition controlling measures was clarified. The last part of the paper was devoted to the discussing of themethods used and the results obtained in this paper, and the necessity of using fully consistent, spatially and chronologically, nonlinear theory in future work was pointed out.