| In order to solve the application requirements of high frequency,high power,high efficiency and miniaturization of O-type high power microwave（HPM）devices.Aiming to the problems of large radius and low cathode emission electric field caused by the ring diode used in O-type over-mode HPM devices,a large-radius high impedance intense current diode is proposed in this thesis.The gradient magnetic field is used to guide the electron beam to change its center radius,so that the intense current diode can work in the state of high impedance and has the characteristics of compact structure.The main research contents and results of the thesis are as follows:1.The transportation of intense current electron beam in gradient magnetic field is studied.According to the electron beam transportation equation,the laws of electron beam fluctuation and electron beam radial velocity fluctuation have been obtained and verified by particle simulation.When there is a gradually decreasing gradient magnetic field in the diode and drift tube respectively,the variation laws of electron beam fluctuation and electron beam radial velocity fluctuation are analyzed by particle simulation.The results show that the gradually decreasing gradient magnetic field in the diode should be avoided as far as possible,which otherwise will lead to the decline of electron beam quality.While there is a gradually decreasing gradient magnetic field in the drift tube,it is helpful to reduce the fluctuation of the electron beam under certain circumstances.In the actual design,it needs to be analyzed in combination with the initial state of the electron beam when it enters the drift tube.2.Three large-radius high impedance diodes with different impedance and drift tube center radius have been designed.Compared with the traditional diodes,without considering the size of the guiding magnetic field,the radial size and axial size are shortened by more than 30%,and the structure of the large-radius high impedance diode is more compact.The cathode emission electric field of the large-radius high impedance diode is more than 25%higher than that of the traditional diode,which is conducive to the uniform emission of electron beam.The larger the working radius and the higher the impedance of the large-radius high impedance diode,the more favorable it is to reduce the size of the diode and improve the cathode emission electric field.Because of the increase of the working radius,the performance of the diode will be higher.3.The effects of magnetic field configuration,electrical parameters and other factors on the transportation characteristics of electron beam are studied.The results show that the guided gradient magnetic field is very important for the transportation of electron beam.The slower the change speed of electron beam radius is,the smaller the radial momentum fluctuation will be.The position of the guiding magnetic field relative to the diode directly affects the initial state when the electron beam enters the drift tube.This position is very important in the design of the diode.Under the condition of constant magnetic field distribution,the higher the diode voltage is,the more conducive it is to reduce the radial oscillation of the electron beam.When the uniform magnetic field in the drift tube is strong enough,the small amplitude change of current will not have a great impact on the electron beam.The introduction of inner conductor is helpful to stabilize the electron beam transportation,and the electron beam eccentricity has little effect on the electron beam transportation.If the inner conductor is subject to cone treatment during the change of electron beam radius,the cone height shall be ensured to fit the electron beam as much as possible.4.A Ku-band triaxial klystron amplifier（TKA）using a large-radius high impedance intense current diode is designed.Under the condition of diode voltage of680 k V,diode impedance of 77Ω,injection microwave of 30 k W and 14.25 GHz,and the guiding gradient magnetic field parameters B1 of 0.94 T,z0 of 9.2 cm,αof 1 cm,B0of 0.6 T,the output microwave power is 1.4 GW and the efficiency is 23%.Compared with Ku-band TKA using traditional diode,the output microwave characteristics are the same under the same conditions,which verifies the feasibility of large-radius high impedance intense current diode.5.The gradient magnetic field has been designed.By introducing permanent magnet cathode and regulating structure,the purpose of increasing axial uniform area and reducing coil size is achieved.The axial length of electron beam transportation path is not less than 450 mm,and the intensity of uniform magnetic field in drift tube is 0.6 T.Through the joint simulation,it is verified that the electron beam can realize the radius reduction process and stable transportation under the gradient magnetic field.Compared with the traditional uniform magnetic field under the same condition,the size of large-radius high impedance intense current diode and its gradient magnetic field is still about10 mm smaller than that of traditional diode and its magnetic field.The magnetic energy consumption of large-radius high impedance diode and traditional diode is quantitatively calculated.Compared with traditional diode,the magnetic energy consumption of large-radius high impedance diode is reduced by more than 10%,and the more obvious the two working characteristics of large radius and high impedance of novel diode,the more reduced magnetic energy consumption.The larger the working radius of the diode,the more magnetic energy consumption is reduced. |
