Theoretical And Experimental Research On Sheet Electron Beam Traveling Wave Tube

Recently,as a traditional O type vacuum electronic device(VED),when the traveling wave tube(TWT)operating band goes to micro-and sub-micro-wave band,the dimension of the device is getting very small due to the size effect,which would arise several problems,such as difficulties of fabrication for such small dimension structures;small beam current since small beam tunnel,which will reduce the property of the device,like the output power and the electron efficiency of the TWT.In order to handle with the aforementioned problems and improve the performance of the device,the sheet electron beam(SEB)is utilized to replace the traditional circular electron beam.Compared with the circular beam,SEB has several advantages,as follows:(1)due to a larger transverse dimension,it can have a larger beam current and larger beam energy with the same current density;(2)because of a larger transverse dimension,it can have lower beam density,also lower space charge effect with the same beam current;(3)it has the capability of making device to higher frequency,higher output power,higher electron efficiency,smaller dimension,integration.Therefore,the sheet electron beam VED can be the great potential high power generator in micro-and sub-micro-wave even terahertzwave band.Among all the slow wave structures(SWSs)that suitable for the SEB,the staggered double vane(SDV)SWS has some obvious advantages:(1)it is metal structure,which allows high power working on the account of good heat dissipation performance;(2)it has the SEB tunnel naturally,which is very suitable for the SEB working;(3)it has some moderate dispersion characteristics,which means wide operation frequency band and high interaction impedance.(4)it has simple geometry structure,which can be fabricated simply and suitable for the Micro-Electro-Mechanical Systems(MEMS)technology.Based on advantages of SEB VED and the SDV SWS,five SEB TWTs are studied theoretically and experimentally in this thesis:(1)a 220 GHz SDV TWT is designed and simulated;(2)a 220 GHz double SEBs high power TWT is designed and simulated;(3)a 220 GHz phase velocity tapered high power TWT is designed simulated;(4)a 35 GHz SDV TWT focused by the closed periodically cusped magnetic(PCM)system is simulated and experimented;(5)a 35 GHz SDV TWT focused by the open PCM system is simulated and experimented The main work and the high-lights of this thesis are as follows:(1)In order to control the backwave oscillation effectively,a novel method of loading the attenuator is proposed,which is simpler and more effective than the original one and has been used in the 220 GHz SEB SDV TWT.For adjusting the shape and the current density of the SEB simply,a modified SEB gun is studied,which can be used for designing the ideal SEB fast by the designers.(2)For resolving the difficulty of designing the input/output coupler in the multi-beam devices,a Y branch waveguide is proposed as the input/output coupler for the 220 GHz double beams high power SDV TWT.(3)In order to improve the output power of the TWT,the phase velocity technology is applied in the 220 GHz SDV TWT successfully,which can be used for adjusting the geometry configuration to re-synchronize the phase velocity of the signal in SWS and the velocity of the spent electrons for reusing the spend electron beam by restarting the effective beam-wave interaction.For resolving the problem that small dimension of input/output coupler is very difficult fabricated,an E-plane bending input/output coupler is designed,which is suitable for the MEMS technology.Moreover,the micro-fabrication process for the THz SWS is primary experimentally investigated and studied by the UV-LIGA technology.(4)A novel small tunable open PCM system is proposed firstly for the 35 GHz SDV TWT.The novel PCM system can be adjusted simply to get the ideal By magnetic value for focusing the wide side of the SEB by adjusting the position of the pole pieces in reality.And a non-uniform open PCM system is optimized for the 220 GHz SDV TWT,which could promise a 100% beam transmission efficiency in the high-frequency system.(5)We successfully designed and made two Ka band SEB TWTs.Designing work includes the optimization of all the operating parameters and the structure dimensions of the high-frequency system and elecro-optical system of TWT.Experiment work contains the fabrication of the SWS,the assembling of the TWT,the measurement of the transmission characteristics of the TWT,the measurement of the transmission efficiency of the electric-optical system,and the measurement of the power of the TWT.