Research Of 420GHz Carbon Nanotube Cold Cathode Gyrotron

In recent years,terahertz technology has received extensive attention in both academia and industrial internationally.As a significant terahertz device devoted to high power system,Vacuum device has been widely studied worldwide.With the increasement of working frequency,the power density increased extensively,traditional vacuum device confronts much more complicated designs on operating voltage,operating current,also applies high complexity on device manufacture.In this background,Gyrotron accept high attention in the field of terahertz device,for its advantage of frequency independency on device size,high power density achievement.These advantages make Gyrotron consistent with the trend of terahertz technology,which is capable to realize high-power operation and considerate simple device design.Nowadays,most Gyrotron terahertz device employ the thermionic cathodes as electron emission sources.However,the thermionic-based device has its intrinsic drawbacks,such as long activation latency,high working temperature and the construction complexity.Compare with this traditional thermionic cathode,we propose a novel field emission(FE)cold cathode,FE cold cathode possesses superiority on low operation temperature,compact device size,short development cycle and excellent portability,which enable FE cold cathode promising candidate for Gyrotron system design.In this thesis,By application of second-order harmonic component,425GHZ carbon nanotube cold cathode gyrotron has been designed and studied.Main work of this thesis is as follows:Firstly,optimized the Electro-optical system according to the target operation frequency.In a certain cyclotron radius,the working current,working voltage,and working magnetic field of the beam-wave interaction system are specified,select the most suitable adiabatic compression ratio to make the cathode of the electron gun in a workable range,and at the same time its ratio of transverse and longitudinal velocity,also the speed dispersion can meet the working requirements of the high frequency area.Through particle simulation to design the magnetron injection carbon nanotube cold cathode electron gun,we finally designed and optimized an electron optical system with an adiabatic compression ratio of 19.5,an electron beam transverse and longitudinal velocity ratio of 1.2,and a lateral velocity dispersion of 6%.Secondly,through the linear theoretical study of the gyrotron,the basic parameters of the gyrotron are preliminarily determined.According to the strength of the beam coupling coefficient,the position of the electron beam radius is first determined to be1.12mm.Then,through the quality factor(QF)of the cavity,the length of the middle uniform section of the gyrotron beam-wave interaction system is determined to be40mm,In the end the approximate position of the magnetic field is selected to be 8.15T according to the distribution diagram of the vibrating current to avoid mode competition as much as possible.After initially determining the basic parameters of the gyrotron,we then simulate and optimize these data according to the nonlinear theory of the gyrotron to obtain a more accurate magnetic field position and voltage.Finally,the gyrotron beam-wave interaction system is simulated and optimized,and the gyrotron linear theory is applied to simulate and optimize the basic design parameters.The gyrotron can be further determined by comparing the output power and the purity of the output spectrum.The required working magnetic field of the tube is8.13T,the working current is 220m A,the horizontal and vertical velocity ratio of the electron beam is 1.2,and the lateral dispersion of the electron beam is 6%.In our design,the gyrotron system worked at TE₀₆₁mode,the working frequency is 425GHz,and realized 22W output power.