| The Cerenkov-type oscillator is one of the most promising sources to generate high power microwave(HPM) due to its remarkable operating stability, high power conversion efficiency and good spectral characters. Compared to S, C, and X bands, Ku band has higher frequencies, which means it has a positive potential for the increasing of the Pf~2 factor. By far Ku-band microwave has been widely used in digital communication field, nevertheless seldom reported in the HPM field. The SWS of the proposed Ku-band generator is designed to be overmoded in order to ensure the gigawatt-class power handling capacity. However, high-order modes and complex mode competitions must be carefully investigated. This dissertation presents a Ku-band overmoded high power microwave Cerenkov oscillator operated at low magnetic field, with which a quasi-single-mode gigawatt class HPM is generated.The main content and results of the dissertation are depicted as follows.Firstly, the dispersion relationship of the rectangular SWS is investigated with the analytical method, polynomial expansion method and the finite element code. Operated the generator in the vicinity of the π-mode, adopted the drift cavity and resonant cavity can enlarged the Q-factor of the device, which is benefit for the decreasing the start current of the operating mode, thus to realize the mode selection and control in the overmoded SWS.Secondly, PIC codes are used to investigate the mechanism of the proposed Ku-band device. The structures of the device are optimized, and the related physical images are presented. The influences of structure parameters and operation parameters on the output performances of the device are investigated. With the optimized configuration, the designed generator with an output microwave power of 1.2 GW, a frequency of 13.8 GHz, and a power conversion efficiency as high as 38% can be achieved, when the diode voltage and current are respectively 540 k V and 5.8 k A. TM01 mode is predominant in the output microwave power, which takes over almost 95% of the power proportion. The highest electric field approaches a value of 0.8 MV/cm. The results of the 3-D PIC code and KARAT code show good agreements of the 2.5-D simulation results.Thirdly, experiments are carried out to investigate the proposed Ku-band generator. The pulsed power accelerator Torch-01 working at voltage of 740 k V is employed to generate relativistic electron beams with peak current of 9.9 k A. With the guiding magnetic field of 0.8 T, the investigated generator produces microwave pulse with a duration of 24 ns, at a central frequency of 13.76 GHz, and with a power as high as 1.1 GW, corresponding to power conversion efficiency of about 15%. The operating mode is well controlled in quasi-single mode of TM01. When 30 consecutive shots are taken with all the parameters unchanged, the average values of the microwave power and power conversion efficiency are 1.05±0.05 GW and 15±1%, respectively, which indicates a stable performance of the device. The asymmetric modes generated in the initial experiments are suppressed by increasing the diode voltage, replacing the material of the cathode, increasing the guiding magnetic field, and improving the concentricity of the device.Finally, investigations of the Ku-band Cerenkov oscillator are further widened. A type of washer-like SWS is designed by introducing the washers/rods structure from the wide-gap klystron amplifier. The dispersion relationship and the longitudinal mode characteristic of the designed SWS are investigated. After numerical optimization, a device with the washer-like SWS can generated a microwave at central frequency of 15.41 GHz, with a power of 1.0 GW, and with a power conversion efficiency of 30%, when the diode voltage of 540 k V and the guiding magnetic field of 0.6 T. In this condition, the highest electric field approaches a value of 0.6 MV/cm approximately. These results pave a way for the higher power and longer pulse applications of this device.
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