Research On Traveling Wave Management Theory Design Of Terahertz Folded Waveguide

Electric micro-vacuum folding waveguide traveling wave tubes(FWG TWTs)are known as high-power terahertz radiation sources with considerable bandwidth,which can be applied to 0.1?1THz and have great potential applications in the terahertz radar,communications,imaging and others.At present,according to developments of terahertz FWG TWTs in China,there are still a lot of key technologies need to conquer.On one hand,FWG TWTs' developing seeks higher and higher frequency.On the other hand,people are exploring new slow wave structures(SWS)with easier achievability or better performance.Combined with 0.345THz electric micro-vacuum FWG TWTs' developing in China Academy of Engineering Physics,a new type of FWG SWS which can greatly improve device's output power,is proposed,and the whole FWG TWT system's theoretical design is realized.Design of Electron gun.Firstly,the trajectories of electronic beam in static electric field or magnetic field are analyzed.Vaughan iterative method is used to complete the initial selection of Pierce gun's geometric parameters for FWG TWT,and then this initial structure is simulated and optimized to ensure output beam's quality from gun satisfy the requirements of beam-wave interaction region.In the design of electron gun,it can be chosen to work under temperature control mechanism or space charge control mechanism,but for actual experimental conditions,gun's output current is limited by these two mechanisms simultaneously.Design of beam-wave interaction structure/slow wave structure.Through theoretical research on dispersion relationship,coupled impedance,small signal theory for FWG SWS,the initial values of main geometric parameters for SWS can be chosen,and 0.345THz SWS structure is preliminarily designed.Then,this initial SWS structure is modeled in PIC software,and nonlinear beam-wave interaction is simulated and optimized.Firstly,SWS's beam optimal voltage is founded,and then the relationships between SWS's gain and electronic parameters,structural parameters,magnetic parameters are obtained.These theoretical analysis and simulation results,will guide SWS's optimum design,and provide theoretical support for SWS's processing and experiments.Propose one new type of high-power,compact FWG SWS with segmentedvariable parameters and its designing principle is given.SWS's dispersion relation and small signal gain curve are analyzed for parameter's chosen and optimization for this new SWS.This paper completes theoretical design and simulation test of 0.345THz two-stage FWG SWS,and it proves that this new type of SWS can indeed greatly improve SWS's output power and gain.For this new FWG SWS,These variable parameters between SWS sections are very less,and the connection of sections is simple,and the new SWS's processing can be realized easily.Influence of engineering and processing factors on device's performance.Firstly,electromagnetic wave's transmission losse due to metal's limited conductivity is analyzed.As metal's processing roughness increases electromagnetic transmission loss a lot,so one modified metal conductivity,which covers the influence of metal surface roughness,is used for loss calculation.Secondly the influences of metal conductivity on SWS's bandwidth and gain are studied by 3D PIC "hot" simulation.Generally,the smaller the roughness is and the higher the conductivity is,then it will make transmission loss be less and gain and bandwidth of SWS be better.Finally,the paper studied the effect of processing factors--exactly the vertical angle's deviation of waveguide side wall on FWG SWS's performance,such as SWS's loss,operating voltage,gain and bandwidth.Results show that,as the deviation angle increases,electromagnetic signal's transmission attenuation increases,SWS's working point drifts,bandwidth becomes narrower,and gain has a sharp decline.But by attempting to adjust beam voltage to find a new optimum condition,SWS can reach higher gain.These results will be helpful for related processing and experiment.Focusing performance of periodic permanent magnetic focusing system(PPM)and simulation of the whole electronic optical system.Firstly,based on the requirements of beam-wave interaction and beam's motion characteristics in PPM,magnetic field's peak value and period length are chosen to ensure beam's transmission performance in PPM,and then PPM's structural parameters are selected accordingly.Secondly,PPM is simulated in software,and the relationships between PPM structural parameters and magnetic field's distribution characteristics on central axis are obtained.Thirdly the whole model of 0.345THz electronic optical system is constructed in software,ensuring a reasonable connecting of gun and PPM,and beam's passing rate is studied.The influence of PPM structure,starting position,PPM period length,peak magnetic field and magnet thickness on beam transmission characteristics are observed.Combined with the experimental model of 0.22THz electron optical system,the integrated model is tested,and beam passing rate is effectively improved by adjusting structural parameters.The results that analyzed by the integrated model of the whole electron optical system will be helpful for its structure optimization and the improvement of beam' passing rate in experiments.In summary,through comprehensive research on key components of FWG TWT,including electron gun,FWG SWS,PPM,the whole FWG TWT's theoretical design are realized.One new type of FWG SWS with segmented variable parameters is proposed,which is verified that can improve SWS's output power largely.The whole design work of FWG TWT in this paper provides theoretical support for FWG TWTs'production,and will guide the tube's processing and experiments,which will accelerate terahertz FWF TWT's development and promote its application in terahertz radar,communication,imaging system and so on.