Design Of G-band Sectorial-shaped Beam Magnetron Injection Gun And Research On Superconducting Magnet

The gyrotron travelling wave tube(gyro-TWT)is an amplifier based on the electron cyclotron maser mechanism.It has high power and broadband,and is widely used in electronic countermeasures and high-resolution imaging radar.As the operating frequency of the gyro-TWT increases,the transverse dimension of the high-frequency structure decreases,which limits the output power of the device.In order to increase the circuit size,researchers proposed open over-mode circuits such as confocal waveguides and photonic band gaps.Due to the azimuthal asymmetry of the fields in the confocal waveguide,a part of the electron beam couldn’t effectively interact with the RF fields and hence the efficiency in confocal waveguide is lower than that in the cylindrical waveguide.Later,sectorial-shaped electron beams were proposed to improve the efficiency.In this thesis,a sectorial-shaped beam magnetron injection gun(MIG)is designed for a G-band confocal gyro-TWT and the characteristic of beam azimuthal drift is investigated.The thermal analysis of superconducting magnets is conducted.Firstly,the theory of MIG and of electron movement under the orthogonal electric and magnetic field are introduced,and the azimuthal drift of the uniform annular electron beam is analyzed.Taking a G-band MIG as an example,the drifting angle of the innerand outer-most electron are 24.4° and 36.1° respectively.The larger the radial distance,the greater of the azimuthal drifting angle is.The azimuthal drift mainly results from the radial electric field and longitudinal magnetic field,and the other fields have little effect about the drift.Secondly,the realization of sectorial-shaped beam and the characteristic of the drift in the E×B field are discussed.By adjusting the emitter shape,a sectorial-shaped beam MIG with a velocity ratio of 1.17 and a velocity spread of 3.4% is designed.The drifting angle of the inner-and outer-most electron are 20° and 45° respectively.By presetting an offset angle of 70° for the sectorial-shaped emitter,the beam distribution is consistent with the mode patterns of the operating mode.At the output of the MIG,the average drifting angle of the beam is 9.5° per 100 mm,and the beam radius changes less than0.04 mm.The magnetic field plays an important role in confining the movement of electrons.Based on our previous work on the design of magnetic solenoid,this thesis conducts a thermal analysis of the superconducting magnet for gyro-TWTs.The conduction heat leakage,radiation heat leakage,and heat leakage on the current lead are calculated,then the amount of liquid nitrogen for pre-cooling is evaluated.Finally,simulation on the temperature distribution of the magnet components is conducted.