Research On Frequency-hopping Relativistic Cerenkov Oscillator Crossing X And Ka Bands Based On Dual Annular Cathode

In recent years,cross-band microwave sources have become an important research direction.However,the existing frequency-tuning device has problems of narrow bandwidth,small band-spacing,and complicated adjustment mode.In this paper,a frequency-hopping Relativistic Cerenkov Oscillator with crossing X and Ka bands based on dual annular cathode is proposed.The device is systematically studied by theoretical analysis and particle simulation method.The research content of the thesis includes the following aspects:Firstly,a systematic theoretical study on the over-mode slow-wave structure(SWS)and its cold-cavity characteristics is carried out.The cold cavity model of the infinitely long coaxial and hollow rectangular SWS is established.Its dispersion characteristics are solved and calculated.The influence of SWS parameters is studied.Based on this,the coupled impedance characteristics of the SWS are studied.Secondly,in order to achieve cross-band frequency hopping,an internal and external double electromagnetic structure based on dual annular cathode is designed.The external electromagnetic structure is used to excite the?mode of the quasi-TEM mode of the coaxial SWS,and the internal electromagnetic structure is used to excite the?mode of the TM₀₁ mode of the hollow SWS.The internal and external electromagnetic structures are isolated from each other,and the working process is relatively independent,increasing the interval of output microwaves.The transverse mode selection is realized by selecting appropriate electron beam parameter and the longitudinal mode selection is realized by introducing the cavity.Combined with the electron beam transmission characteristics and the cyclotron resonance absorption phenomenon,the common guiding magnetic field is calculated.In the particle-in-cell(PIC)simulation,a 2.5-dimensional full electromagnetic simulation program is used to systematically study the mechanism of high-power microwave generation of the device,and a detailed physical image of the beam-wave interaction process is given.Firstly,the internal and external electromagnetic structures are separated,and particle simulation research is carried out independently,focusing on solving the problem of beam-wave efficiency improvement.When the diode voltage is550 k V and the external and internal beam current is 8.9 Ka and 4.4 k A,Simulation results show that the X-band microwave with a power of 1.50 GW and a frequency of8.41 GHz is generated,corresponding to an efficiency of 34.9%.Meanwhile,the Ka-band microwave with power of 740 MW and frequency of 31.30 GHz is generated,corresponding to efficiency of 30.5%.A coaxial dual annular cathode on-line adjustment technical scheme is also proposed.Under the condition that the microwave source vacuum chamber is not opened,the electron beam generated by the inner and outer cathodes is adjusted only by adjusting the extension and retraction of the inner and outer cathodes.Further,the feasibility of simultaneous implementation of dual-band internal and external is explored,and the pre-cavity is introduced to suppress microwave leakage.Simulation results indicated that the output power levels for the X-band and Ka-band were 1.47 GW and 710 MW,respectively,and the efficiencies were 34.2%and 30.7%,respectively.In addition,the simulation results of the2.5-dimensional program were verified using a 3-dimensional program.Finally,in order to verify the feasibility of the technical solution,the pre-experimental optimization design for the X-band is carried out,taking into account the high efficiency and low magnetic field.Typical particle simulation results show that output microwave center frequency is 8.42 GHz,output power is 1.58 GW,beam-wave interaction efficiency is 35%.A preliminary experimental study was carried out.When the diode voltage was 580 k V and the guiding magnetic field was 0.6 T,the output microwave frequency was 9.4 GHz,the power was about 200 MW,and the microwave pulse width was 22 ns.The causes of excessive frequency drift and low power were analyzed and improved.