Investigations Of A Compact L-band Coaxial Relativistic Backward Wave Oscillator

The backward-wave oscillator (BWO) is one of the promising devices that can produce high-power microwaves and is intensively investigated because of its merits such as compact structure, high efficiency and good stability. Now there are many reports on BWOs that operate in the frequency regime of X-band (8GHz-12GHz) or C-band (4GHz-6GHz), but reports on L-band (1.12GHz-1.70GHz) are rare. However,the BWO operating in the frequency regime of L-band is of interest to this field. In the non-coaxial BWO of L-band, the radius of the slow-wave structure is very large, and the volume and weight of the guiding-magnetic system are also very large. Thus, the non-coaxial BWO of L-band is bulky and lumbersome and is inconvenient for real application. Studies show that the radius of the coaxial L-band BWO can be smaller than that of the non-coaxial L-band BWO. The coaxial BWO of L-band can be very compact and convenient for real application. So investigation on the compact coaxial L-band BWO is of great interest to the high-power microwave field.First,the present thesis gives theoretical investigations on the coaxial BWO using the linear fluid model. The TM mode dispersion equation of the coaxial BWO in the infinite guiding-magnetic field is derived and solved numerically. The dispersion curve, operating frequency, and the growth rate are obtained. The results show that both of the growth rate of the TM01 mode are lager than those of the other modes. So the coaxial BWO will have a good property if it operates in the TM01 mode. In order to have a good design, it is necessary to analyze the dispersion relation of the TM01 mode and determine its operating parameters varying with geometrical structure of the BWO.Secondly, based on the theoretical investigations, a coaxial BWO is designed which operates in the frequency regime of L-band. And its interaction process is analyzed. The results show that the radius of the slow-wave structure can be much smaller in the coaxial BWO case than in the non-coaxial BWO case. The TM01 mode of the coaxial BWO has no cut-off frequency, which is similar to the TEM mode in the conventional coaxial waveguide. It is paid attention to that the longitudinal component of electric field of the coaxial TM01 mode can be strong, differing from the TEM mode in the conventional coaxial waveguide. So the coaxial TM01 mode can have much strong interaction with the electron beam. To verify the results, the 2.5D KARAT code is used to simulate and analyze the non-linear interaction of the L-band coaxial BWO. Much useful knowledge is obtained such as the growing of electromagnetic wave ,...