Study On A Novel Magnetically Insulated Transmission Line Oscillator

A novel magnetically insulated transmission line oscillator (MILO) using a vircator as load (V-MILO) is put forward for the first time in the present dissertation. The special feature of such vircator-load MILO is that, besides generating the self insulating magnetic field in the slow wave structure, the load current is used to form virtual cathode oscillation in the vircator load and gives out additional microwave radiation making the V-MILO a higher efficiency microwave source. One type of the V-MILO, called CV-MILO, which uses an outward-emitting coaxial vircator (CV) as load, is studied systematically by theoretical analysis, particle simulation and experimental measurement, and a series of valuable results are obtained.According to the Maxwell equations and the Floquet theorem, the dispersion relation of the coaxial slow wave structure in MILO is analyzed, and the relations between the operating frequency and the structure parameters are obtained. The results show that changing the cathode radius would not influence the frequency of MILO, so the impedance can be adjusted conveniently by changing the cathode radius without frequency altering. The physical properties of the outward-emitting coaxial vircator in the CV-MILO are investigated, and we find that under the intense modulation of the externally injected microwave, the frequency and the phase of the outward-emitting coaxial vircator are locked by the driven microwave, and the power of the locked vircator increases as the injected amplitude enhanced. The support-leg system in the extractor coax region of MILO is studied with field matching theorem, and from the results we can conclude that, for certain frequency, if the first cut-off mode in the extractor coaxial waveguide is Hn1, then the number of the support legs should be n.Particle simulation method is used to study the properties of four types of MILO, including the basic physical process of the beam-wave interactions and the dependence of the microwave radiation on the structure parameters and the beam parameters. The CV-MILO and its corresponding conventional structure using a coaxial diode (CD) as load, called CD-MILO, are investigated particularly. The simulation results predict that, the CD-MILO could generate an average power of 2.6GW with efficiency of 12% at the beam parameters of 520kV, 41.5kA, while the CV-MILO would yield a higher average power of 3.2GW with efficiency of 15% at the similar beam parameters of 510kV, 41.4kA. The frequencies of both the MILOs are the same 3.9GHz.In the primary experimental studies of the CV-MILO and CD-MILO, the microwave power, the frequency, and the mode are measured, and the relations between the microwaveradiation and the beam parameters are investigated. In the experiments, an output microwave power of 300MW with efficiency of 1.3% is got from the CD-MILO at the beam parameters of 550kV, 43kA, and a higher power of 510MW with higher efficiency of 2.3% is obtained from the CV-MILO at the beam parameters of 540kV, 42kA. Both the CV-MILO and the CD-MILO export microwave in coaxial TEM mode at 5GHz.In conclusion, the simulations and the experiments, though there are some differences in their results, all confirm that the vircator-load CV-MILO can gain higher microwave power with higher efficiency than the conventional CD-MILO.We are exploring a feasible way to improve the efficiency of the MILO in this dissertation, and we hope that it will also be helpful to study other microwave sources.