A Multi-stage Depressed Collector For G-band Sheet Beam Traveling-Wave Tubes

In recent years,terahertz(THz)traveling-wave tubes(TWTs)have advanced quickly due to their high power,high efficiency,and broad bandwidth.However,the rise in frequency and decrease in size of key components have hindered the enhancement of power and efficiency of TWTs.The cross-section of a sheet beam is broader than that of a round beam.With the same current,the current density of a sheet beam is lower than that of a conventional round beam,and the space charge effect is weaker,which can boost the power of THz TWTs.Simultaneously,a multi-stage depressed collector(MDC)is one of the significant methods to enhance the efficiency of THz TWTs.Particularly for THz TWTs,due to the limited interaction efficiency,it is even more indispensable from the optimized design of MDC.To enhance the overall tube efficiency of a THz TWT—G-band sheet beam TWT,this thesis examines the single-stage depressed collector and investigates approaches to enhance the collector’s efficiency.Additionally,a single-stage depressed collector is suggested,manufactured,and assembled.Building upon this,a high-efficiency elliptical four-stage depressed collector is put forward.The primary focus of this thesis is outlined as follows:1.The electron beam’s position,velocity,and energy distribution information at the inlet of the depressed collector is extracted.Based on the optimized design,a single-stage depressed collector is achieved.Considering the secondary electrons,the collector achieves an efficiency of 90.08% and a reflux rate of 1.75%.Following depressed recovery,the overall tube efficiency increased from 4.23% to 34.68%.The simulation results demonstrate that the collector’s voltage drop and shape design are reasonable.To conduct the entire tube experiment,processing and assembly drawings were created,and the production of parts,welding packaging,and initial insulation and airtightness tests were carried out.2.Taking into account the unique properties of the sheet beam,an elliptical fourstage depressed collector is devised to enhance the efficiency of the depressed collector.Employing the simulated annealing algorithm for programming calculations,the optimal solution for voltage drop and current at each stage of this four-stage depressed collector is obtained.Consequently,the recovery efficiency of the four-stage depressed collector reaches 98.11%.By employing CST software for simulation calculations,the impact of elliptical eccentricity on the efficiency and reflux rate of the four-stage depressed collector is examined.Ultimately,when the eccentricity is 0.6,the efficiency attains its peak while the reflux rate achieves its minimum.Considering the contribution of secondary electrons,the collector efficiency stands at 92.43%,resulting in an overall tube efficiency of 36.85% and a reflux rate of 0.02%.The simulation results clearly indicate a substantial improvement in the performance of the elliptical four-stage depressed collector compared to the single-stage depressed collector.3.Utilizing the ANSYS module for steady-state thermal analysis,the assembly model of the single-stage depressed collector was subjected to simulation,yielding a temperature distribution ranging from 33.42℃ to 329.83℃,with an average temperature of 230.41℃.The simulation outcomes demonstrate that the operating temperature falls within the normal range.Building upon this,a steady-state thermal analysis of the elliptical four-stage depressed collector is conducted.The resulting temperature distribution spans from 119.66℃ to 696.39℃,with an average temperature of 351.41℃Notably,the first stage exhibits the highest temperature,while the fourth stage displays the lowest temperature.These simulation results establish a groundwork for designing the subsequent assembly model and devising an effective heat dissipation structure.