Investigation In Basic Theory Of Coaxial Virtual Cathode Oscillator And Principle Experiment

Compare to numbers of high power microwave (HPM) sources, the virtual cathode oscillators (VCO) have many special merits, such as, simple structure, high peak power ability and the high allowance of poor electron-beam (e-beam) quality and so on. These characters make it easy to be developed into a convenient, reliable and compact HPM sources. The research of VCO attracts extensive attention of scientists all over the world, especially scientists working in the field of military science and technology. Types of improved VCO have appeared in the last two decades, such as, reflex triodes, reditrons, vircator with e-beam modulation, resonant cavity frequency locking vircators, multi-vircator phase locking devices, etc. Nevertheless, due to the beam-wave interaction space is general asymmetric and the processes of beam-wave interaction are quite complicated with high-order nonlinearities, up to now, a conclusive theory which could describe the physical processes in detail and could give out a universal scaling law of the VCO devices has not been obtained. The pretty low beam-wave conversion efficiency, the frequency shift from shot to shot, and the uncertainty of the output microwave power are still the main drawbacks of the VCO type HPM sources. CVCO (Coaxial Virtual Cathode Oscillator) is a new type of VCO emitting electrons radially and it is superior to the traditional VCO. Since the end of last century, people have extensively studied the coaxial virtual cathode oscillator, but the extent and depth have not reached those of the axial virtual cathode oscillator.As an effort of studying the inherent physical laws and improving the performance of the CVCO type devices, this dissertation supported by the National 863 program thoroughly studied the basic theory of the coaxial virtual cathode oscillator theoretically, experimentally and by particle simulation. Main jobs and contribution done by this dissertation are as follows:First, the rules of penetration and reflection of e-beam, the parameter relationship and their impacts on the beam-wave conversion efficiency have been thoroughly studied by comparing the sameness and differences between the CVCO and the VCO. Old theory of virtual cathode oscillator has been summarized and supplemented in detail.Second, comparing to the axial virtual cathode oscillator, the coaxial virtual cathode oscillator has been studied by PIC simulation method in detail. With the conclusion of the principle of the coaxial virtual cathode oscillator, we has brought forward one new kind of coaxial virtual cathode—radial three-cavity coaxial virtual cathode oscillator whose peak period-averaged power reaches 2.45 GW and the beam-wave conversion efficiency is about 12%. The output microwave has high mode purity and narrow bandwidth.Third, with some experimental results on the coaxial virtual cathode oscillator, by using theoretical analysis and numerical simulation methods, it is carried out in detail that the formation of the output microwave on the coaxial virtual cathode oscillator. Results show that the output microwave modes of the coaxial virtual cathode oscillator are mainly composed of TM₀₁ mode and TE₁₁ mode and the proportion of TM₀₁ mode is about 66%～75% while the proportion of TE₁₁ mode is abut 25 %～34%, which accord with the results of the experiment very well.Fourth, the resonator mechanism of the coaxial virtual cathode oscillator has been investigated in detail. Some experiments show that the interaction between the virtual cathode oscillator and the cavity is a key in determining the output microwave power and propagating modes. Particularly, we observe that the e-beam plays an important role in the cavity formation. The alterable resonator theory has been firstly brought forward to explain the physical mechanism of the coaxial virtual cathode oscillator and it accords with the results of the experiment on the whole.