Simulation Investigation Of Smith-Purcell Superradiation Drived By Two Electron Beams

Terahertz(THz)refers to a kind of electromagnetic wave whose frequency ranges from 100 GHz to 10 THz and the wavelength ranges from 30?m to 3mm,and there are some coincidence parts between its band and the band of millimeter wave,sub-millimeter wave and infrared light.The special location in the spectrum makes the terahertz wave have many properties which make terahertz technology have broad application prospects in a lot of fields.The study of terahertz radiation sources is the key of the development of terahertz science and technology,and taking advantage of vacuum electronics is an effective way to design terahertz sources.However,the development of the miniaturized electric vacuum devices is restricted by the starting current.This paper,therefore,proposes a method to reduce the starting current by using a special waveguide structure which is composed by grating and sub-wavelength hole arrays.The following words are some specific contents of this thesis:(1)This paper proposes a kind of special waveguide structure composed of grating and sub-wavelength hole arrays and deduces the dispersion equation of the structure in the cold cavity condition.Then the paper draws the curve of the dispersion and compares the influence of different parameters on the dispersion characteristics.(2)This paper draws two dispersion curves of the structure by using the simulation software CST and particle simulation software relatively and compares them with the theoretical dispersion curve.In combination with the dispersion curve,an appropriate working point is set and a set of parameters are designed.By utilizing these parameters,the special structure can generate 100 GHz surface wave and 200 GHz superradiation wave when the applied voltage is 35 kv.In addition,we compare the starting current in three conditions: one electron beam goes through the grating,one electron beam goes through the special structure and two electron beams go through the special structure.On the basis of the first set of parameters,another set of parameters is designed so that the structure can generate 300 GHz surface wave and 600 GHz superradiation wave under the 50 kv voltage.Similarly,we compare three cases of starting current.By combining the simulation results of two sets of parameters,the thesis proves that the starting current could be reduced by making two beams go through the waveguide structure composed by grating and hole arrays.(3)This paper analyses the influence of lateral dimension on the dispersion and propogation pattern of wave in the periodic structure and designs a set of parameters in three dimension condition.By using these parameters,the structure can generate 137 GHz surface wave and 274 GHz superradiation wave when the applied voltage is 18 kv and the incident current is 30A/cm2.