Simulation And Design Of Three-stage Depressed Collector For G-band Travelling Wave Tube

Terahertz technology has broad application prospects and has become an important cutting-edge technology in the world.In recent years,many countries have invested a lot of special funds in terahertz technology research.Terahertz traveling wave tube(TWT)has become one of the most potential terahertz source due to its advantages of high power,small size and wide bandwidth.Due to the limitation of its working principle,the electronic efficiency of the TWT is very low.After the interaction,the electrons enter the collector,and its remainder kinetic energy,which can be recovered by the depressed collector to improve the efficiency of the whole tube,dissipates on the collector surface in the form of heat.In this paper,the depressed collector of 0.22THz folded waveguide TWT is designed.The three-stage depressed collector is studied based on the single-stage depressed collector.The main contents of this paper are as follows:1)The working principle of the collector is introduced,especially the generation mechanism of the secondary electron and whose influence on the collector and suppression methods.2)The experimental result of the TWT with the single-stage depressed collector is compared with that of simulation,which verifies the correctness of the author's simulation method.3)the principle and function of magnetic refocusing are introduced.According to the state of the electron beam at the entrance of the collector,it is determined that the refocusing magnetic field is not used in the scattered cluster region.The voltage setting is estimated to obtain the highest collector efficiency according to the energy distribution of the electrons.Then the axisymmetric three-stage depressed collector,whose efficiency and back streaming current are respectively 90.43%,and 0.533mA,is optimized by simulation.4)The electrons returning to the slow wave structure will affect the beam wave interaction and introduce noise.By changing the entrance of the second electrode of the axisymmetric collector into an oblique structure,an asymmetric electric field can be generated,which can be used to change the trajectory of the electron and reduce the back streaming current.By optimizing the oblique angle and potential setting,the efficiency and the back streaming current of the asymmetric three-stage depressed collector can be respectively greater than 89.01%,and less than 0.089mA.