Simulation Research On 300GHz Carbon Nanotube Cold Cathode Gyrotron

In recent years,with the development of terahertz?THz?science and technology,gyrotron has been widely studied as an terahertz vacuum electronic device.The fast wave device gyrotron is based on the radiation theory which is excited by electrons cyclotron resonance.Its operating frequency range is very wide from the millimeter wave to terahertz wave band.Gyrotron has been widely applied in fields of microwave weapons,plasma heating,radar,advanced accelerators,communication,due to its capability of generating continuous wave power and high pulse peak power.Most of the traditional gyrotrons employ the thermionic cathodes as electron emission sources.However,in the practical application,the development of thermionic-based devices has been somewhat restricted because of their intrinsic drawbacks,such as preheating,large size and limited lifetime.In contrast,the field emission?FE?cold cathode technology has excellent performance,which is manifested in the miniaturization and integration of devices,the instantaneity,and the decrease of power consumption of the system.Carbon nanotubes?CNT?are ideal FE cold cathode candidates owing to their low processing cost,impressive chemical and temporal stability and high emission current density.In this thesis,300 GHz carbon nanotube cold cathode gyrotron has been designed and studied.The main work of the thesis is as follows:CNT cold cathode electron optical system applying to 300GHz gyrotron has been studied.In this system,the magnetic injection electron gun has been adopted.A beam radius of 0.292mm is investigated firstly,which is the first wave peak of beam-wave interaction coupling coefficient in the cavity.In the PIC simulation,a magnetic injection carbon nanotube cold cathode electron gun is designed.The influence of magnetic field in cathode area,emitter ring length,the first anode voltage,and the second anode voltage on the electron beam is analyzed.A magnetic injection CNT cold cathode electron gun with 40.5kV/100mA is developed.The spread of perpendicular and parallel velocities are 4.5%and 5%,and the velocity ratio of electron beam is 1.3.Then,the second wave peak of beam-wave interaction coupling coefficient is adopted in order to increase beam current,the average beam radius is 0.845mm,In the PIC simulation,a magnetic injection carbon nanotube cold cathode electron gun operation on the second wave peak is designed.The influence of magnetic field in cathode area,emitter ring length,the first anode voltage,the second anode voltage on the electron beam is analyzed.A magnetic injection CNT cold cathode electron gun with 35kV/200mA is developed.The spread of perpendicular and parallel velocities are 3%and 4.5%,and the velocity ratio of electron beam is 1.3.Compared with the first electron gun,the higher beam current can be obtained,but the mode competition could be serious.The gyrotron linear theory is adopted to study the beam-wave interaction of the gyrotron.The structure size,working mode and start-up current of the resonant cavity are determined by calculation.The influence of the magnetic field vs.the output power with the first wave peak electron beam operation is analyzed.The output power is maximum at the magnetic field of 11.45T.Results of beam-wave interaction simulation show that the TE₀₃ mode at the frequency of 301 GHz is oscillated.An output power of410W is obtained.The beam-wave interaction efficiency is approximately 10%.The influence of the magnetic field vs.the output power of the second wave peak electron beam is analyzed.The output power is maximum at the magnetic field of 11.35T.Results of beam-wave interaction simulation show that the TE₀₃ mode at the frequency of 301 GHz is oscillated.An output power of 900 W is obtained.The beam-wave interaction efficiency is approximately 12.9%.