Research On Terahertz Radiation Source Based On High-order Mode

The research of terahertz radiation sources has always been a key technology for the development of terahertz science,and vacuum electronic devices are one of the important terahertz radiation sources.As the frequency increases,high-order mode operation is an effective method for high frequency vacuum electronic devices to overcome the frequency limitation.Mode competition is a key problem that needs to be solved in the work of high-order mode.The electron beam passes through the subwavelength hole array structure from the inner tunnels to generate narrow-band enhanced Smith-Purcell radiation.Based on this radiation characteristic,a new idea to overcome the mode competition in high-order mode operation was proposed,and the working circuit was designed.The main content of this thesis is:The thesis first analyzes the characteristics and reasons of the narrow-band enhanced Smith-Purcell radiation generated by electrons passing through the sub wavelength hole array structure.Then,the characteristic parameters related to vacuum electronic devices are introduced,which provides a theoretical basis for the subsequent research and design of terahertz radiation sources by combining the radiation with vacuum electronic devices.Based on the above-mentioned narrow-band enhanced radiation phenomenon,a new design method is proposed to overcome the mode competition of high-order mode working vacuum electronic devices.First,when the array period is determined,the long side of the hole can adjust the peak frequency of Smith-Purcell radiation,determine the value of the long side of the hole according to the working frequency of the expected device,and set the main-frequency-band of Smith-Purcell radiation.Then,according to the corresponding relationship between the height of the resonant cavity and the frequency of the higher-order mode,a suitable resonant cavity is designed.Finally,with a suitable output structure,the cavity circuit design is completed.According to the above method,we designed a radiation source working in TM_51-2? mode and the frequency of 468GHz,and obtained a simulation output of more than 10W.And further explored the design method to overcome the mechanism of mode competition.In order to study the applicability of the design method,from two perspectives,the radiation source working in different high-order modes was quickly designed.First of all,keeping the sub wavelength hole array unchanged,changing the height of the resonant cavity,so that the TM_31-2? mode and the TM_71-2? mode corresponds to the main-frequency-band respectively,and the radiation source working in the TM_31-2?mode and the TM_71-2? mode is designed.If we keep the height of the resonant cavity unchanged,adjust the value of the long side of the hole to change the main-frequency-band of the Smith-Purcell radiation so that it corresponds to the TM_31-2? mode and the TM_71-2? mode respectively,and we can also control the radiation source to work in the TM_31-2? mode and TM_71-2? mode.Compared with the cylindrical electron beam,the sheet electron beam has many advantages in the high frequency range.In this thesis,the sheet electron beam is used to design a working circuit with a working frequency of 350GHz and a working mode of TM_51-2? mode,and an output power of 205W is obtained.The Smith-Purcell radiation mechanism is introduced into the design of the interactive cavity circuit structure to make it work in high-order mode while suppressing mode competition.This provides an important and feasible design idea for the development of vacuum electronic devices in the direction of terahertz.