Investigation Of A P-band Magnetically Insulated Transmission Line Oscillator (MILO)

The magnetically insulated transmission line oscillator (MILO) is a coaxial crossed-field device. It has many potential applications because of its high power, relatively high efficiency, simple structure, using no external magnetic field, low impedance, pure frequency spectrum and so on. In recent years, the L-band and the C-band MILO have been investigated both numerically and experimentally. Many literatures show that the gigawatt level high power microwaves have been generated experimentally. However, the MILO device with frequency less than 1GHz is rarely investigated. It may be mentioned that the HPM source with frequency less than 1GHz still has very important applications in both military and industrial fields, therefore research on the compact P-band MILO device is certainly interesting. This thesis presents preliminary investigation on the P-band MILO using linear theory, particle simulation, and experimental design. A series of valuable results are obtained from this work.Theoretically, the TM mode dispersion curve of MILO SWS is obtained by solving its dispersion equation numerically. The result is very important because it can give us the approximate dimensions of the main SWS for a MILO device that can work in frequency range of P-band. We can use these approximate dimensions of the SWS in the particle simulation code to start the optimum design process of the P-band MILO device.In the particle simulation, with the use of the 2.5D fully electromagnetic particle-in-cell (PIC) code, four types of P-band MILO are investigated. (1) the MILO is studied based on the load-limited model, including the dependence of microwave radiation on the structure parameters and the beam parameters; (2) the electromagnetic structure of the P-band load-limited MILO is improved, and the simulation result shows that a 640MHz, 5.17GW high power microwave is obtained when the beam energy is 540keV and the beam current is about 56kA. The efficiency is about 17%. The total length of P-band load-limited MILO is about 42cm and its diameter is about 44cm; (3) a P-band load-limited MILO with a more compact structure is simulated. The device uses only five SWS vanes, which include only one RF choke vane, making it more compact. The simulation result shows that a 640MHz, 5.46GW high power microwave is obtained when the beam energy is 550keV and the beam current is about 57kA. The efficiency is about 17.4%. (4) a P-band tapered MILO is presented in simulation. When the beam energy of 550keV and the beam current is about 57kA, a high power microwave are abtained from the model with frequency of 640MHz and output power of 6GW.The power conversion efficiency is anout 19.1%; (5) the hybrid MILO using the advantages of tapered MILO and load-limited MILO is proposed and investigated in the present thesis. The simulation results show that a 640MHz, 4.27GW high power microwave is obtained in the simulation when the beam energy of 550keV and the beam current is about 57kA. The efficiency is about 13.6%. In the experimental design of the whole system, we design the device considering three aspects that are the matching with accelerator, the radiation system, and the engineering intrgration. The radiation system is designed using a high-frequency-field numerical simulation software, which provides many functions such as simulating mode converting from TEM to TM01, keeping the output waveguide and the space impedance in matching, making the inner and the outer conductor grounded, and mechanically supporting the inner conductor. The efficiency of the radiation system is more than 95%. In the last part of this paper, the engineering design of P-band load-limited MILO is presented, considering the simulation result and the design of radiation system.These results in this thesis are of interest to potential the application of the P-band high power microwave generated with the magnetically insulated transmission line oscillator in the future.