Investigation Of A High Power Millimeter Wave Generator Operated At Low Magnetic Field

More and more attention has been paid to millimeter wave because of its intrinsic advantages in many aspects. And slow wave devices have been used widely for their high efficiency, simple mechanism and stability. At present, researches on high power millimeter wave are still at initial stage. So a millimeter wave overmoded high power microwave generator is designed in this dissertation. And it can be operated at a relatively low magnetic field to generate microwaves with high efficiency and compact structure.The dispersion relationship is theoretically analyzed for the slow wave structure (SWS). Field-matching method and Polynomials-expanding method are used to investigate the dispersion characteristics of the SWSs and the dispersion curve is plotted. The dispersion features under different structure parameters are studied. And this will help to design the device.Strong magnetic field is usually needed to confine electron beam in conventional slow wave devices, but in practical use, lower magnetic field will be more convenient. So the feasibility of low magnetic field operation is investigated. And a relatively low magnetic field is selected according to Particle-in-cell (PIC) simulation.PIC simulation is used to investigate the mechanism of generating HPM. The detailed beam-wave interaction process is analyzed with the help of the 2.5-dimensional PIC code, KARAT. The influence of structure parameters and operation parameters on the performances of the device is investigated, such as SWS ripple depth, the number of the periods of the two SWSs, the length and radius of the output cavity, the beam voltage and the strength of the external guiding magnetic field. Under the optimized configuration, a microwave of TM01 mode at 33.41GHz is generated in simulation with diode voltage of 700kV, beam current of 6.28kA and guiding magnetic field of 0.73T. The microwave generation begins to start at the 6th nanosecond (ns), and its saturation time is 8ns. The average power after saturation is 930MW and the efficiency is over 20%.